# Memory Boy problem



## NGroeneveld (Jan 23, 2011)

Well in my first Kijiji deal gone bad, I've got myself a dud Memory Boy. It just makes really weird noises. At the lowest feedback setting you can hear repeats but they are at a different pitch than the original note, one higher and one lower. Turning up the feedback really makes it pretty wild. Any ideas?

What is really pissing me off is the knobs do not come off with gentle prying, so I cannot open it up to check for bad connections.


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## mhammer (Nov 30, 2007)

Is it this one?


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## NGroeneveld (Jan 23, 2011)

that looks like it


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## gtrguy (Jul 6, 2006)

Is the modulation depth control cranked? That could make for some seasick repeats...


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## NGroeneveld (Jan 23, 2011)

gtrguy said:


> Is the modulation depth control cranked? That could make for some seasick repeats...


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## NGroeneveld (Jan 23, 2011)

gtrguy said:


> Is the modulation depth control cranked? That could make for some seasick repeats...


oh - you mean the depth control knob on the outside - I was thinking you meant a trim pot on the inside. 

adjusting the depth control does not resolve the issue.


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## mhammer (Nov 30, 2007)

There should be 7 trimmers on the board. I can see 6 in the picture and perhaps one is hidden. In four-BBD delay pedals, the arrangement EHX used was an individual bias trimpot for each delay chip, a gain-adjust trimmer after delay-chips 2 and 4, and a "balance" trimmer at the output of the 4th chip. The bias trimmers set a DC voltage that the audio signal has to ride on the way into the delay chip. If a little high or low, the chip will distort but still pass audio signal. If too high or too low, it does not pass audio signal, distorted or otherwise. There is a little bit of signal loss in the chip, so EHX includes a small booster stage between chips 2 and 3 to bring the level back up, andone of those trimmers adjusts the small amount of boost applied.

Each delay chip has two parallel paths inside that are stitched together at the output. The "balance" trimmer on the last chip adjusts the relative level of each of those two paralllel paths. When adjusted perfectly, the clock, which drives the chip and can work its way into the audio, is mostly cancelled out.

This is a complete shot in the dark for me, in the absence of an audio clip or other diagnostic information, but if the balance trimmer were a little off, yu would most likely get a sort of high-pitched "ghost" tone that corresponded to the delay-time setting; higher pitch with shorter delay. One would expect it to be exaggerated as feedback is increased, and that ghost now re-enters the audio path at the start.

But, like I say, that's a blind guess.


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## NGroeneveld (Jan 23, 2011)

Okay thanks - a new one at Long and Mcquade is 140 plus tax - so it's probably more worth while to just pick up a new one and write this off rather than trying to get it fixed


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## mister.zed (Jun 8, 2011)

NGroeneveld said:


> At the lowest feedback setting you can hear repeats but they are at a different pitch than the original note, one higher and one lower.


There's that old joke in engineering about it only being a bug until you document it - then it's a feature! Call this a mod and enjoy it!


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## mhammer (Nov 30, 2007)

NGroeneveld said:


> Okay thanks - a new one at Long and Mcquade is 140 plus tax - so it's probably more worth while to just pick up a new one and write this off rather than trying to get it fixed


1) The knobs are just press on. That doesn't mean that won't be snug, but you should be able to pry them off with suitable tools. Even a flathead screwdriver should be fine.
2) I'm happy to walk you through an attempt to salvage it, but I guess you know your patience level and pocketbook better than I do.


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## NGroeneveld (Jan 23, 2011)

mhammer said:


> 1) The knobs are just press on. That doesn't mean that won't be snug, but you should be able to pry them off with suitable tools. Even a flathead screwdriver should be fine.
> 2) I'm happy to walk you through an attempt to salvage it, but I guess you know your patience level and pocketbook better than I do.


Thanks - I did get the knobs off but I got the name of a local repair guy so will take it to him for an estimate


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## mhammer (Nov 30, 2007)

Personally, I would start with the balance trimmer, and explore other things from there. Somebody else started a conversation with me here regarding their Deluxe Memory Man, which would appear to have the same schematic as your Memory Boy, give or take a piece. That unit employs the larger MN3008 chips, where yours uses the smaller version. Same chip underneath.
DMM-MN3008.png


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## cboutilier (Jan 12, 2016)

mhammer said:


> 1) The knobs are just press on. That doesn't mean that won't be snug, but you should be able to pry them off with suitable tools. Even a flathead screwdriver should be fine.
> 2) I'm happy to walk you through an attempt to salvage it, but I guess you know your patience level and pocketbook better than I do.


My favorite method for removing pot knobs is a pair of teaspoons.


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## NGroeneveld (Jan 23, 2011)

mhammer said:


> Personally, I would start with the balance trimmer, and explore other things from there. Somebody else started a conversation with me here regarding their Deluxe Memory Man, which would appear to have the same schematic as your Memory Boy, give or take a piece. That unit employs the larger MN3008 chips, where yours uses the smaller version. Same chip underneath.
> DMM-MN3008.png


I'll try the balance trimmer


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## NGroeneveld (Jan 23, 2011)

mhammer said:


> Personally, I would start with the balance trimmer, and explore other things from there. Somebody else started a conversation with me here regarding their Deluxe Memory Man, which would appear to have the same schematic as your Memory Boy, give or take a piece. That unit employs the larger MN3008 chips, where yours uses the smaller version. Same chip underneath.
> DMM-MN3008.png


I tried the balance trimmer and that just makes the problem sound different. How do you get the circuit board out of the housing? It seems that the power supply input won't let the pots come through. Can get it halfway out then it hangs up


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## NGroeneveld (Jan 23, 2011)

Of course five minutes after posting that question it came to me - so I have the whole thing apart now


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## Guest (Jan 30, 2018)

NGroeneveld said:


> Of course five minutes after posting that question it came to me - so I have the whole thing apart now


Take pictures as you go.


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## mhammer (Nov 30, 2007)

NGroeneveld said:


> I tried the balance trimmer and that just makes the problem sound different.


Welcome to troubleshooting 101. Now you can say "At least I know it's not _that_." Sometimes, you have to start with the simplest, least intrusive things, simply to be able to cross them off the list before engaging in anything more elaborate. - the stompbox equivalent of asking "Are you_ sure_ you plugged the vacuum cleaner in?".

I'm going to ask a simply dumb question of my own: how do you know you were adjusting the balance trimmer? I'm not questioning your chops. I just need to know for myself that I can confidently cross that part off my list of suspects.


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## NGroeneveld (Jan 23, 2011)

mhammer said:


> Welcome to troubleshooting 101. Now you can say "At least I know it's not _that_." Sometimes, you have to start with the simplest, least intrusive things, simply to be able to cross them off the list before engaging in anything more elaborate. - the stompbox equivalent of asking "Are you_ sure_ you plugged the vacuum cleaner in?".
> 
> I'm going to ask a simply dumb question of my own: how do you know you were adjusting the balance trimmer? I'm not questioning your chops. I just need to know for myself that I can confidently cross that part off my list of suspects.


In the other post I think you said it was #4 - now on rereading I'm seeing that it may be #7


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## mhammer (Nov 30, 2007)

Yes, #4 is likely to be either a bias trimmer (which mis-setting will result in either total delay signal loss or a more distorted delay signal) or a gain-setting trimmer, which will adjust delay level a bit and potentially overdrive a subsequent delay chip. For whatever reasons, EHX saved the balance trimmer for right at the end of the delay chain. That may or may not align with the part number given.

How can you tell which one it is? The balance trimmer will connect to pins 3 and 4 of whatever delay chip it is connected to. Those are the output pins of the chip. The trimmer will adjust their relative levels to cancel out clock whine.

I don't know if it's necessarily a better explanation/description than what I've provided here, but you can find a different and more comprehensive description here: Behind the Bucket Brigade | Premier Guitar

And yes, the 'm' is for Mark.


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## NGroeneveld (Jan 23, 2011)

mhammer said:


> Yes, #4 is likely to be either a bias trimmer (which mis-setting will result in either total delay signal loss or a more distorted delay signal) or a gain-setting trimmer, which will adjust delay level a bit and potentially overdrive a subsequent delay chip. For whatever reasons, EHX saved the balance trimmer for right at the end of the delay chain. That may or may not align with the part number given.
> 
> How can you tell which one it is? The balance trimmer will connect to pins 3 and 4 of whatever delay chip it is connected to. Those are the output pins of the chip. The trimmer will adjust their relative levels to cancel out clock whine.
> 
> ...


Thanks Mark - I'm going to leave the pedal for now as I've got some guitar building things that need to get done


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## mhammer (Nov 30, 2007)

No problem. So do I!


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## NGroeneveld (Jan 23, 2011)

mhammer said:


> No problem. So do I!


thanks for your input!


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## fatchingarito (3 mo ago)

mhammer said:


> Is it this one?


 Looks like your are missing trim7


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## fatchingarito (3 mo ago)

mhammer said:


> Is it this one?


You are missing trim7 entirely


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## mhammer (Nov 30, 2007)

I see it. It's way over on the left0, between that cluster of black wires and the jack.


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