# Taking a small problem and making it worse - think I blew something



## Granny Gremlin (Jun 3, 2016)

So a bud dropped me his Traynor TS-25 again. I had fixed it before (tripping breaker - not a fuse like the schem; replaced the output chips and some diodes) but now the reverb wasn't working. Checked a few things and think cleaning the jacks/plugs to/from the tank was doing it, but I did not bolt down the tank as I powered on to test. It slipped and hit the heat sink fin of the TIP105 output chip. Bit of a spark and now it's tripping the breaker again. *$%! Feel like such a boob.

Anyway, checked a bunch of things; nothing looks burnt. The TIP105 tests fine. Replaced it anyway (had one in the parts bin) but still the same. Tested a few things around the 105 and the power supply but everything looks good on the meter. I don't have a TIP100 so I tried a TIP102 on the other side of the push pull output - that wasn't it either.

Anyone have any ideas as to what I could have burnt? Starting to think it's the breaker itself.


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## RBlakeney (Mar 12, 2017)

definitely the ground lugs.


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## Latole (Aug 11, 2020)

To me, schematic show a breaker not a fuse.

Link to schematic;


http://www.lynx.net/~jc/790124_TS25_iss2.gif



You make a short at TP105 and you talk about TP100 and TP102. Sorry I can't follow.


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## Paul Running (Apr 12, 2020)

If the heatsink is not electrically insulated from the 105's collectors, that may explain the spark. Did you check the current draw through the output transistor emitters? Verify the DC balance for the output devices.


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## Paul Running (Apr 12, 2020)

Rod Elliott of ESP has a good blurb on complementary symmetry power amps.


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## Granny Gremlin (Jun 3, 2016)

Latole said:


> To me, schematic show a breaker not a fuse.


You're right, my mistake, but the schem says 1A - it's a 1.5 in the actual amp



Latole said:


> You make a short at TP105 and you talk about TP100 and TP102. Sorry I can't follow..


Yes, the 105 is right next to the reverb tank. I tried replacing it. The other chip is a 100; didn't have a spare but I did have a 102 (equivalent part; just some higher ratings) so I tried subbing that in. Longshot, I know, but both output chips are heat sinked to the chassis so there's a chance a transient through the chassis took out the other chip.




Paul Running said:


> If the heatsink is not electrically insulated from the 105's collectors, that may explain the spark. Did you check the current draw through the output transistor emitters? Verify the DC balance for the output devices.


There is a plastic film (and thermal compound) between the chip and the chassis. I checked for conductivity between base and chassis (base is connected to the heat sink fin on the chip). When the (grounded) reverb tank touched it, it could have hit the fin directly, so the insulation is moot. Also when I subbed in new devices for both I had them flying in the air just to be sure - the workbench is in the cold basement and the amp wouldn't be on long enough for them to overheat.

I did a diode check from base to emitter and collector, forwards and backwards. The readings were in the same ballpark on the original chip and the new one(s) - .5xx drop from B to C and .6xx from B to E (and nothing when backwards). Between that and subbing new devices, can't we be sure the chips are fine and not the issue?

How do I check the current draw when the amp won't stay on for more then 3 seconds? Bypassing the breaker seems like a bad idea, and would it make sense to check that when off?

Anyway, this morning it occurred to me that the transient could have gone the other way; the least resistance could be not through the chip but through the tank to the preamp board. That is separate board from the power amp and supply - on the back of the pots so can't see obvious bunt things when normally mounted. Will go have a look at that in a bit. 

Incidentally, it's hard to tell for sure because the amp only stays on for 3 seconds or so, but I think it's all hum and no signal in those 3 seconds.


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## Paul Running (Apr 12, 2020)

Granny Gremlin said:


> all hum and no signal in those 3 seconds


The power supply is severely overloaded...filter caps cannot keep up with the current demand, hence the hum. Unfortunately, 3 sec is not enough time for thermal probing. Probably a good time to begin isolating circuits which usually means desoldering components, unless the active devices are in sockets.


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## Paul Running (Apr 12, 2020)

You could start by removing the rails from the power amp just to verify that the power amp is the culprit.


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## dtsaudio (Apr 15, 2009)

You did diode check from B-E and B-C. Did you check C-E? Failure mode for darlingtons is usually C-E. The internal protection diode shorts.
The base is NOT the heatsink. The collector is. Check continuity between the tab and the heatsink directly.
Take out the TIP100, and 105. If you have a bulb tester plug the amp into that. Turn on the amp. Does the fuse blow or the lamp glow.
If good, measure the voltage where the base should be on the outputs. You should get about -1.5V, +1.5V. If good, you have blown the output transistors (yes, they are transistors, not chips).
If those voltages are out, then you have blown something further upstream,


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## loudtubeamps (Feb 2, 2012)

Paul Running said:


> You could start by removing the rails from the power amp just to verify that the power amp is the culprit.


And for troubleshooting use an AC current limiter bulb supply......


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## Granny Gremlin (Jun 3, 2016)

Wow there's some good stuff to chew on - thanks.

I think my light bulb current limiter is not working so gotta take a look at that first , but I can check the E to C on the chips. Again I find this unlikely to be an issue because subbing in new chips (without a repeat incident) didn't help, but easy enough so might as well.


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## Granny Gremlin (Jun 3, 2016)

Alright, so what @dtsaudio said about the heat fin connection made me take a quick look at the datasheet and yes collector is connected to the heat fin - I had the pinout wrong (assumed middle as base but it's the leftmost one - was getting readings assuming middle as base so assumed that was correct, but in retrospect the polarity was wrong for PNP vs NPN). Alright so checking those all over again...


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## Granny Gremlin (Jun 3, 2016)

OK so retested the chips:










So if I am looking at this right, either being in circuit ("in C") affects some readings or at least the TIP100 is buggered (I did at one point replace it with a 102 to no avail). I would not understand why the new 105 is no good vs the original that tests fine out of circuit (but maybe changing them out a few times yesterday I lost track of which one is which). I also don't understand why both new 107s (never used) have readings for B(+) to E.

Anyway off to look at my current limiter.


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## Paul Running (Apr 12, 2020)

Granny Gremlin said:


> I also don't understand why both new 107s (never used) have readings for B(+) to E.


You're measuring the series internal emitter resistors of the Darlington pair.


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## Paul Running (Apr 12, 2020)

Take a look at the monolith for the TIP105 and predict what you should measure with your DMM.


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## Granny Gremlin (Jun 3, 2016)

Riiiiiiiight.... so why don't I see that on the 105s? ... or the 102s (except with B(-) to E)? ... and if it's resistance, why does the meter probe polarity matter? ... and why do I get no reading if I switch from diode mode to R on the meter?

These are tangents I suppose but I am trying to learn and understand things better.

Anyway the current limiter is fine. No glow at all when I run a ss Peavey through it but it is 100-200 watt bulb, could only find frosted so hard to see, and no power if I unscrew the bulb. Wiring looks correct when I opened her up with the bulb in series ahead of the black live wire in front of the limited socket. Last time I tried it, it must have been with a bad bulb/not screwed all the way in, or plugged the wrong power cord in or something.

So off to desolder the transistors and poke voltages (@dtsaudio said they're not chips but if they are de facto an integrated circuit of 2 transistors, 2 resistors and a diode doesn't that make it a chip technically?).


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## jb welder (Sep 14, 2010)

RBlakeney said:


> definitely the ground lugs.


You just can't let go can you. That reminds me of the time you caught the guy saying his reverb ad was up for 2 years but it had really been up for 3 years.


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## jb welder (Sep 14, 2010)

Disconnect the speaker until the breaker stops popping and you have 0volts DC on the output.


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## Granny Gremlin (Jun 3, 2016)

So removed the output devices and turning on makes the current limiter light up (well that sure works eh) keeping the breaker from tripping so could measure things. Even still turned it off right away - clipped meter leads in place, hands off, and then turned on just long enough to get a read.

Measuring the DC V at both collector wires (neg probe at AC cord ground lug) I get -1 and +5 respectively for the PNP and NPN. So I am looking upstream of the TIP100 for the issue vs the 105 as I was previously. 




jb welder said:


> Disconnect the speaker until the breaker stops popping and you have 0volts DC on the output.


Little late for that now (transistors removed) but I did try powering on before with no speaker cuz I got lazy between swapping out the transistors - breaker kept going every time. I did not have a meter across the output at the time though.


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## Paul Running (Apr 12, 2020)

Granny Gremlin said:


> why does the meter probe polarity matter?


What setting is your DMM set to?


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## Granny Gremlin (Jun 3, 2016)

Paul Running said:


> What setting is your DMM set to?



Diode check. Tried DC R after you explained but no reading that way, which also seems odd if it's just pure resistance there going around the internal transistor pair.

Anyway, the only thing upstream from the collectors are the filter caps; can't check those because above my meter's range (can't even visually confirm value bc they were installed with the labelling down to the PCB). The Anodes look dirty / not quite rusty, but similar to that, on both of them. Getting 4VAC off the PT secondary.

I did check the rectifier diodes yesterday (even removed one from circuit) and they seemed fine, but I think I have replaced those before on this same amp (used 4007s vs 3s cause didn't have 3s and wasn't gonna put 1s in there).


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## dtsaudio (Apr 15, 2009)

Disconnect the transformer secondary, (you can leave the center tap connected) and measure the AC from the center tap to either secondary lead. They should be the same voltage
You should get about 18VAC on each. If you're not, either there is a short somewhere on the primary side, or the transformer's pooched.
Your DC voltages are way off, but you want to isolate the transformer in case something is pulling the voltage down. Verify that that works first.


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## RBlakeney (Mar 12, 2017)

jb welder said:


> You just can't let go can you. That reminds me of the time you caught the guy saying his reverb ad was up for 2 years but it had really been up for 3 years.


And look at what happened to HIM. 😆


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## jb welder (Sep 14, 2010)

RBlakeney said:


> And look at what happened to HIM. 😆


Got deep sixxed?


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## Granny Gremlin (Jun 3, 2016)

dtsaudio said:


> Disconnect the transformer secondary, (you can leave the center tap connected) and measure the AC from the center tap to either secondary lead. They should be the same voltage
> You should get about 18VAC on each. If you're not, either there is a short somewhere on the primary side, or the transformer's pooched.
> Your DC voltages are way off, but you want to isolate the transformer in case something is pulling the voltage down. Verify that that works first.



That was a pain. One of the secondary leads broke off so it may have been frayed just under the insulation there where it's not obvious and been part of the problem.

Anyway, getting 20VAC on both sides when disconnected (and that one lead stripped back a bit to get a better connection and have something to solder back later).


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## Paul Running (Apr 12, 2020)

You're narrowing it down, now you just have to find the node that's pulling all that current.


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## dtsaudio (Apr 15, 2009)

As an addendum to checking voltages, check to be sure chassis ground (earth), is connected to power supply ground, otherwise you'll get incorrect voltage readings. Some amps seperate the two.
Your ultra low readings suggests they are seperate.


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## Granny Gremlin (Jun 3, 2016)

dtsaudio said:


> As an addendum to checking voltages, check to be sure chassis ground (earth), is connected to power supply ground, otherwise you'll get incorrect voltage readings. Some amps seperate the two.
> Your ultra low readings suggests they are seperate.



Yeah I did - AC input ground to chassis has continuity to PT centre tap and all othe other obvious ground points both signal and power rails.

Gonna go reconnect the PT now and see what I can see.


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## Granny Gremlin (Jun 3, 2016)

K so I get that the current limiter can affect the PT output voltage but 4VAC (1.5 and 2.5 a side from the tap) seems real low. Bypassed the limiter and it ramped from 12 to 14 (end to end not halves at the tap) before the breaker tripped. That's still low right?

With the limiter I'm getting like +5 and -1 VDC on the other side of the rectifier as well as the filter caps. I wonder if I put that diode back in the wrong way around after I pulled it to check yesterday... the before pics I took to avoid such things say no, but maybe one of the diodes is just bad and I missed it.

I actually have a TS-15 here I could compare things to - very similar amp. Same output devices just no reverb, weird master volume switch (more of a power attenuator vs the pre line driver pot on the 25) and the operating voltages are bipolar 22 and 15 vs 25 and 14. .... hmmm different PT tho.... and I'm not sure that guy is working right either.


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## jb welder (Sep 14, 2010)

This is still with no output devices and no speaker?
The more current the amp pulls, the more the bulb lights up, the lower the voltage that gets to the unit under test. 
12 to 14VAC end to end with no bulb limiter is still quite low.


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## Granny Gremlin (Jun 3, 2016)

jb welder said:


> This is still with no output devices and no speaker?
> The more current the amp pulls, the more the bulb lights up, the lower the voltage that gets to the unit under test.
> 12 to 14VAC end to end with no bulb limiter is still quite low.



Correct - no output devices connected and therefore no speaker.

With the limiter that bulb is ON I tells ya. I guess I gotta poke around to see where the current is going, like it must be just pouring into a ground somewhere right?


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## Granny Gremlin (Jun 3, 2016)

I'm seeing almost 2A from either side of the PT to chassis ground (limiter in effect). When I probe one particular side of the PT the bulb brightness is greatly affected - so much so that I noticed from peripheral vision. Probing the other side obviously affects it too but not nearly as much - didn't notice until I went back to compare looking directly at it. ... so I think I'm back to looking at half the bridge rectifier not working properly or am I wrong? ... or the filter cap on the - 25V rail to ground since that's the rail that is ridiculously low and powers the TIP105, which was the thing that shorted momentarily when I fat fingered the reverb tank?

I'm in half a mind to not bother figuring that out and just repopulating the entire power supply but I don't have the caps.


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## dtsaudio (Apr 15, 2009)

So let's isolate things.
Pull the two resistors before the zener diodes. That'll isolate the power amp from the preamp and its power supply. At least you'll know it's either power supply or power amp.


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## jb welder (Sep 14, 2010)

Granny Gremlin said:


> I'm seeing almost 2A from either side of the PT to chassis ground (limiter in effect). When I probe one particular side of the PT the bulb brightness is greatly affected - so much so that I noticed from peripheral vision.


Maybe I'm mis-reading but it sounds like you are in current mode with your meter. If so, you can only use your meter that way if you break the circuit and insert the meter in series. Otherwise probing directly in current mode will likely end in smoke and tears. 
Meter in current range is basically a straight piece of wire with a probe at each end.


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## Granny Gremlin (Jun 3, 2016)

Those zeners are on the daughter (preamp) board vs the main (power supply and power amp) board. Easier to just disconnect the 2 connecting wires than pulling resistors..... one of which comes off the TIP100 supply (same point that feeds collector), but the other is a ground.... don't understand where the -14 rail is coming from. And I only see 1 680Ohm resistor (2 zeners backwards oriented tho). Gonna have to trace this a bit.

... no that wasn't a ground it was the -25 rail after all (2nd junction which the +25 rail doesn't have - that wire to the preamp comes off the same point as the wire to the TIP100 collector - no idea why they didn't tap the -25 rail the same way, I guess so the leads come off the the board next to each other vs 2 inches apart and they can twist them the whole way) but it also has continuity to ground which is what confused me (fluctuates quite a bit and inconsistantly but seems to settle in the 1.3-2Ohm range jumping around a few decimal places vs stable). The +25 rail does not have continuity to ground at all. That explains the significantly lower voltage on the -25 rail. So, if I just disconnect the negative rail to the preamp board, and I still have continuity to ground there, then the problem can't be in the preamp, right? The less desoldering the better.


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## Granny Gremlin (Jun 3, 2016)

So desoldered the -25 rail to the preamp board and I am still getting continuity to ground from that rail so notthepreamp. That's a bit of a relief because that board is much more densely populated.

I better go eat something. And feed the dog.


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## jb welder (Sep 14, 2010)

So that 1 to 2 ohm resistance reading should appear across the 2200uF cap on the (-) rail.
The cap and the 2 diodes of the bridge feeding it are about the only possible things to give a reading that low. Unless a wiring or solder fault.


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## Granny Gremlin (Jun 3, 2016)

Exactly so. I typed this last night, but forgot to hit the post button:

So I was looking over the schem as I ate and I see nothing in the power amp where a single component failing short would cause a ground leak from the -25 rail. So I ran downstairs and tested the R on the filter caps. The first gave 12M and the second was a dead short, so looks like I'm replacing some filter caps (may as well do both). Now I just gotta go get some somewhere.


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## Granny Gremlin (Jun 3, 2016)

... and it turns out that the TIP100 NPN has been obsoleted and the big suppliers have none left. For some reason not the equivalent/complimnetary TIP105 PNP (or much of the rest of the series). I guess I"ll need to find out if the 102/107 are a good substuitute combo at some point. People keep bringing me these now that they're popular - got a TS-15 to look at next - and I got nothing better to do.

Thanks for the help and education. Again. Y'all the best. I'll update once I source some caps.


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## jb welder (Sep 14, 2010)

Granny Gremlin said:


> I"ll need to find out if the 102/107 are a good substuitute combo at some point.


They are a perfect sub for the 100/105 and a bit of an upgrade. They are basically the same part with a higher voltage rating. So like replacing a cap with the same value but higher voltage rating.
100V vs 60V.
Datasheet attached covers the whole series.


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## Granny Gremlin (Jun 3, 2016)

jb welder said:


> They are a perfect sub for the 100/105 and a bit of an upgrade. They are basically the same part with a higher voltage rating. So like replacing a cap with the same value but higher voltage rating.
> 100V vs 60V.
> Datasheet attached covers the whole series.



That's what thought, but I haven't been trusting myself lately.


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## Granny Gremlin (Jun 3, 2016)

So while I'm sourcing caps I thought I'd take a quick look at the TS-15 because maybe it needs parts too.










Damn - not even gonna turn this MF on until I sort this out. That blue wire is soldered on one end and just hooked through the eyelet (not even twisted) on the other. Why do people do shit like this?

Also one of the speakers says "4.9" Ohms just to be weird. Schem calls for 4 Ohm total, and shows only 1 speaker so I guess I'll try series for 8ish.


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## Paul Running (Apr 12, 2020)

Granny Gremlin said:


> Why do people do shit like this?


Probably because they don't know any better, they don't care or maybe lazy.


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## dtsaudio (Apr 15, 2009)

I like the red wire just hanging there - not!
Be prepared for more surprises inside.


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## Paul Running (Apr 12, 2020)

Granny Gremlin said:


> So while I'm sourcing caps


Are they axial or radial caps that you require?


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## Granny Gremlin (Jun 3, 2016)

dtsaudio said:


> I like the red wire just hanging there - not!
> Be prepared for more surprises inside.


Ye olde dangler to nowhere. Always a good sign.



Paul Running said:


> Are they axial or radial caps that you require?


Axials, which are always more of a pain. I'd put in radials but none of the leads are long enough so it'll get a bit ghetto. Hole spacing is 6cm.


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## Paul Running (Apr 12, 2020)

Granny Gremlin said:


> Axials, which are always more of a pain. I'd put in radials but none of the leads are long enough


Yeah, I prefer the radials myself, put them in a clamp, mounted away from the main heat currents and not have to worry about vibrations and other hostile effects. Back in the 80s and early 90s, I salvaged a bunch of stereos that people were throwing out. I kept all the PS caps...3300µfd @ 50V was a common cap.


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## Granny Gremlin (Jun 3, 2016)

Yeah, I've salvaged caps but got nothing even close right now. I'm all about the recycled audio - I have a pile of Stackpole SPST sliders, 100n tropical fish caps, and a jarfull of knobs among other things from an old dead solid state Traynor mixer.

Anyway, I measured the TS-15 speakers DCR because 4.9 was just too weird and the jumpers between the 2 drivers look original and it would only require 1 for series. That 4.9 is the DCR (measured a tad higher) so they're 8 Ohm speakers. Removed the stupidity and get a total DCR of 2.9 in parallel so that sounds about right for 4 Z load.

Went to go plug it in and see what's up and:









It's gonna be one of those, I see. And I'm all out of mains plugs. Might cannabilise an IEC cable, but think I only have shorties at home. Know I got a new plug at the studio for emergencies (as well as longer IECs) and I'll be going there later.


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## Paul Running (Apr 12, 2020)

A shame about the plug...don't you hate it when you see that done?
Here's the ones I would use when I was on the Chip Amp craze. They fit a nice low profile. Salvaged from a Japanese stereo brand amp. I got a lot of my salvaged caps from a lad named Shawn at Computer Recyclers old location. A good lad...he knew his cap salvaging tricks. Anyhow, they were plentiful in the late 90s:


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## Granny Gremlin (Jun 3, 2016)

Well, I got some caps (3300 50V) and put them in but same issue (preamp and output transistors still disconnected) - looks like I need to change out the rectifier diodes as well. The original cap may have been fine, but probably good I changed them out as they were under spec (35V vs 40 on the schem) as well as 50 years old.

I could only find radials (without paying triple and waiting for shipping) but the leads were long enough so fine. Will reinforce them structurally with hot glue a la original Traynor spec ;P

Whole new power supply coming up.


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## Granny Gremlin (Jun 3, 2016)

That did it; no more tripping breaker/lighting up the current limiter. While I was there I cleaned off the solder side of the PCB cuz flux/scorching all over the rectifier area (I have replaced those before because 2 diodes were visibly burnt - used 4007s again vs the original 4003s; 54xx won't fit the through-holes) and it looks like there may have been just the tiniest whisker of a solder bridge from one side of the PT to a trace coming off one the diodes. Don't think that was the problem but it was too close for my liking so cleaned that up while I was down there.

Now to reconnect the output transistors and test.

The TS-15 is up next after that - turns out it just needed the speaker wiring sorted out, new 3 prong plug and the volume/master pot/switches were not working right (jumpy/non-linear response and noisey). Tried cleaning all the switches and pots - and that seems to have fixed the master but the volume pot will need to be replaced. Hilariously empty chassis on that one; figured they'd use the same power amp/supply board but no; all smaller parts (esp the filter caps) on a pot-mounted board up against the front; the rest of the chassis is empty aside from the PT and output transistors all alone in the middle.


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## Granny Gremlin (Jun 3, 2016)

The 25 is now all good including the reverb.

The 15 was a a fun time. Apparently the master switch was never bad/dirty, it was the treble pot right next to it all along - all 4 solder joints (3 lugs + structural leg) were cold joints on the PCB, so when you pushed the switch, the board would flex and it would drop out of the circuit momentarily.

Then a hullabaloo with replacing the bad volume pot with... another bad pot apparently. Never had a brand new pot not be good but it was one that was kicking around the parts bin for a decade so... As you moved it around (flying on leads vs PCB mount legs) the R would change or drop out. Wasted an hour on that weirdo cuz I thought 1) I goofed and the third lug was needed, then 2) trying to figure out if the structural leg was connected to anything because it was solderered to an actual ground trace, but no, then 3) was it the leads I put in, or 4) was there some cold joint around the pot that would pop open when the board flexed (see above re treble pot). Once I sorted that out all was good, but now the volume is solid shaft vs knurled (all I had left - the one knurled one Ihad was the bad one). The original knobs for this thing were long gone anyway so no biggie, just gotta use set screw vs push ons now. Owner has opted for white chicken heads which get the kids' seal of approval.

Then there's this - the power resistors on the master volume (power attenuator) switch. I should replace them because that looks suboptimal, but I don't have them (will order, cuz I see the dude all the time and I'm sure this thing will come back at some point for something) and it actually works fine - musta just got reeeeeeally hot one time (I guess those ceramics dissipate heat pretty well - not so much the PCB).


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## Granny Gremlin (Jun 3, 2016)

Oh and the new filter caps (and diodes) in the 25:










vs the old:


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## jb welder (Sep 14, 2010)

Granny Gremlin said:


> Then there's this - the power resistors on the master volume (power attenuator) switch. I should replace them because that looks suboptimal, but I don't have them (will order, cuz I see the dude all the time and I'm sure this thing will come back at some point for something) and it actually works fine - musta just got reeeeeeally hot one time (I guess those ceramics dissipate heat pretty well - not so much the PCB).


The narrower 5W resistor is a newer style replacement. I'd wager the original one burnt and that is what discoloured the board.


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## Paul Running (Apr 12, 2020)

jb welder said:


> the original one burnt and that is what discoloured the board.


That one was close to ignition...a good reason to raise those power resistors a bit and install thermal insulators underneath.


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## Granny Gremlin (Jun 3, 2016)

So both the physical resistors and the schem say 2 of those power resistors are "OR51" - what the hecking heck does that mean? 5 x 10^1? That seems high for them always hanging off the TIP outputs in series no matter the switch position.


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## Paul Running (Apr 12, 2020)

Granny Gremlin said:


> OR51


UK method for 0.51Ω...5,100Ω is noted as 5K1Ω; the letter is the decimal point and it can be R, K, M...


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## Granny Gremlin (Jun 3, 2016)

Thanks, I knew about the letter being the decimal thing, but the 0 threw me off - thought it was an O. Doi.


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## Granny Gremlin (Jun 3, 2016)

Forgot to post this.


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## Paul Running (Apr 12, 2020)

Lot's of fun, eh?


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## Granny Gremlin (Jun 3, 2016)

The reverb stopped working on the TS-25 so she's on the bench again.

Crashing on the tank does nothing so output issue.

Checked the usual things, the jacks clean and tight. Still noffin.

Checking continuity from RCA tip to where the wire hits the PCB is good on the output, but open on the in. Might have an in and out issue. Great.

Tank is an Accutronics 1FB2B1B, so that's 1.475k input and 2.25k out (Untitled Document)

I measure 185 Ohms on the input transducer, but get wild jumpy readings on the output in the 10s-100s of MOhms range, so that's buggered right? I"ll also have to rewire the input cable but that's the easy bit.

Went back to check the output and now the output is measuring in the hundreds of ohms but still jumpy, varies between 100 and change and 400.


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## Paul Running (Apr 12, 2020)

Granny Gremlin said:


> Went back to check the output and now the output is measuring in the hundreds of ohms but still jumpy, varies between 100 and change and 400.


Got an eye loupe or powerful eye glass? Mighty fine wire on those coils; if the coil wire has partially separated from the lead-out wire: a soft touch, good gripping tweezers or forceps and a steady hand with the iron...and a short prayer.


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## Granny Gremlin (Jun 3, 2016)

OK so the weird thing is now it measures stable at about 190R and after changing the wire on the input I have verb... the tank still doesn't crash tho, like you smack it and nothing, which is odd.

I'll see if I can find my magnifying glass and have a look at that transducer; perhaps something intermittent happening. It was on this very amp where I once had to reconnect the lead from one of the transducers to the RCA jack because it sheered off (also very flimsy).


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## Granny Gremlin (Jun 3, 2016)

Huh, the tank won't crash because the spring assembly is so small and light that the suspension actually works 100% (vs a typical type 4 or 9 tank where it merely takes the edge off) - smacking the tank around from the outside does nothing but you can crash the springs if you smack them or the sub-plate directly.


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## Granny Gremlin (Jun 3, 2016)

Think the transducer is fine. It's all taped up nice and even after a shake test I can't get the reverb to stop working. I was probably touching dirty/oxidised contacts on the inside of the tank with my meter probes before I cleaned everything.

Problem was just the input wire RCA connector which has been replaced.


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## Paul Running (Apr 12, 2020)

If you have a dog, they'll let you know...our dogs go nuts when I bang the tank.


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## Granny Gremlin (Jun 3, 2016)

Maizey is too polite (aka traumatized rescue). She won't make a peep for outies or being fed or hardly anything.


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