Help solve my Deluxe Memory Man wierdness?

[honkyjonk]

I have a DMM where the echo works, but is very weak. Also, the feedback knob doesn't do anything (perhaps because the echo is so weak)

It used to be that I could get the strong (normal) echo back by turning it on and off. But eventually it would revert to the current state. Now it's just like that all the time.

Anyway, any ideas as far as what that could be? I have sockets so replacing chips is just a matter of taking it apart. The problem does not seem to be U1. I've replaced that with a TLO72, then gone back to the original just to confirm that it made no difference.

Wish I had a schematic for you all, but haven't been able to find one with a brief search.

[Scruffie]

Please provide this info: http://www.diystompboxes.com/smfforum/index.php?topic=60421.0


Schematic:

[honkyjonk]

Thanks for the schematic Scruffie,

Is there more info I'm supposed to provide? I don't want to irritate anybody. I have read that page now.

What components should I be looking at concerning the problem described above?

[Scruffie]

Voltages would be a good start

Is it a 70s model or reissue? The on and off fix possibly suggests a bad cap.

[honkyjonk]

It's not a 70's (blue?) version. It's black.  I don't really know exactly what year it's from. It looks like this one: http://www.guitartoneoverload.com/wp-content/uploads/2010/07/GTO_memoryman_digitaldelay.jpg

I have quite a bit of experience replacing elecrolytic caps, so I suppose I could give that a shot. And I'll look for the 15.7 volts.

[Scruffie]

Shoulda said 70's/80s (the blue is usually the 4 knob version which is a different design) assuming it doesn't have the power lead it's most likely a reissue, unless you're from Canada/Europe.

It's possible it's a bad cap but replacing them all blindly isn't necessarily going to solve the issue, debugging it first with voltages and then audio probing is the best way to fix the issue.

So once again, could you take voltages from the unit or if you prefer, follow the debugging link on the tabs at the top of the page, audio probe and find the area you're loosing signal and then take voltages there.

[honkyjonk]

Okay,

I'm getting -14.9 Volts to pin 4 of all the DIP 8(4558) chips except U5 which has -15.04 at pin 4.

Here are the voltages for the dual input and output pins for U1-U5.

U1
p2 -7.5V
p3 -7.5V
P6 -7.5V
p7-7.5V

U2
p2 -3.1V
p3 -3.1V
P6 -6.7V
P7 -6.7V

U3
(all readings the same as U1)

U4
p2 -7.5V
p3 -7.5V
p6 -6.9V
p7 -6.9V

U5
P2 -7.1
P3 (won't stay still. Fluctuates between -6V and -8V)
p6 -7.1
p7 (won't stay still. Fluctuates between -6V and -8V)

Am I seeing oscillating on U5?
Swapping new chips in for U5 and U2 (which seems to have some lower voltages going on) doesn't seem to change anything.

[Scruffie]

Could you please provide the full voltages, 571, 3005s and all.

U2 is suspect but I don't know if that's the half of the opamp biasing the following BBD or being biased by the companders output.

U5 oscillates because it's the LFO.

[honkyjonk]

Okay,

Here's the MN3005's

U7
1 0V
2 -7.5
3 -7.6
4 -7.6
5 -15.02
6 -7.5
7 -6.9
8 -14.1

U8
1 0V
2 -7.5
3 -7.1
4 -7.2
5 -15.03
6 -7.5
7 -6.7
8 -14.1

the 571

1 -13.7
2 -13.05
3 -13.05
4 -14.8
5 -13.05
6 -13.05
7 -4.05
8 -13.06
9 -13.06
10 -6.9
11 -8.6
12 -13.06
13 0V
14 -13.06
15 -13.06
16 -13.9

and the 4047 chip

U9
1 -6.2
2 -8.8
3.-8.7
4 0V
5 0V
6 0V
7 -15.03
8 -15.03
9 -15.03
10 -7.5
11 -7.5
12 -15.03
13 -6.2
14 0V

[Scruffie]

Right... the compander output is possibly a little low but nothing definitive, otherwise your voltages all look fine.

Now you need to break out an audio probe (follow the debugging page tab up top regards building and using one) and find where your signal is dropping off, test in this order which should be right according to the factory schematic;

U1 Pin 1
U1 Pin 7
U6 Pin 7
U2 Pin 1
U2 Pin 7
U3 Pin 1
U3 Pin 7
U4 Pin 1
U6 Pin 10
U4 Pin 7

[honkyjonk]

Hey Scruffie,

Sorry it took me a couple days to get around to this, and thanks so much for the help. I'm getting nothing at U1 pin 1, nor pin 7. I checked and rechecked, and verified that the probe was working properly.

So I backed up and probed at pin 2 of U1, still nothing. I get signal before the first cap (.1uF) but I don't have anything right after that cap.

I also noticed that while I don't have signal on the (-) side of the 22uF cap (47uF in my case) which is connected to pin 1 of U1, I DO have signal on the (+) side of that cap, the side that is connected to the direct out via a 150R resistor.

Does this sound like a bad input cap?

[Scruffie]

You wont get signal on an inverting opamp input, that's quite normal, but none on the output pins isn't normal.

Just to rule out the very obvious... you did have the input level turned up and the pedal engaged when you checked that didn't you? I hate to ask but we all make these mistakes!

You say you tried replacing U1 already so that rules out it being a bad opamp...

If you have the pedal on as normal and turn the blend to the full dry side do you get signal then?

Just checking some other stuff, is yours a true bypass model? When turned off do you get your bypass signal and is it controlled by the input level pot?

[honkyjonk]

Just to rule out the very obvious... you did have the input level turned up and the pedal engaged when you checked that didn't you? I hate to ask but we all make these mistakes!

Yes, there's no signal with the switch engaged, nor without it engaged for that matter, and yes the volume was up.

You say you tried replacing U1 already so that rules out it being a bad opamp...

Yes. I think I'm on the third one now, so probably not . . .

If you have the pedal on as normal and turn the blend to the full dry side do you get signal then?

Yes I tried all the way dry, all the way wet, inbetween. Nada.

Just checking some other stuff, is yours a true bypass model? When turned off do you get your bypass signal and is it controlled by the input level pot?
True bypass. No the volume doesn't have any effect when in bypass, and I can play through it when it's turned off.

[Scruffie]

You say no signal without the switch engaged but say you can play through it when it's turned off? So does the bypass work? If not it sounds like it's the foot switch.

[honkyjonk]

Sorry for the confusion.

Yes, the bypass does work. I didn't mean to imply that I have no signal through the unit. There's just no echo (or a very weak echo I should say)
The dry signal is present at the output when the MM is engaged and also when it's in bypass.

No signal was referring to an inability to tap the signal at pin 1 at U1.  BTW,  Pin 1 starts at the top left of the IC when looking down at the front (side with markings) right? Just making absolutely sure I'm measuring the correct pins.

[honkyjonk]

Is the next thing you're going to ask, how am I getting signal through the unit if I'm not getting it at the output of U1? Hmmmm

[Scruffie]

Yup, top (marked by the ICs notch) left is pin 1.

So with the pedal active, the level pot does still work, just not with the probe? Yeah sounds like you're making a mistake with the probe.

[honkyjonk]

Well,

I can clearly get signal using the probe at the input jack, but not on the other side of C1, nor the aforementioned pins on U1. At U1 pin 1, I get a loud popping sound and then it seems like a power drain (volume of noise goes down) and no signal in the amp. But if I disconnect the cable from the probe and put it back into the echo out jack, I'm getting signal (just without the crazy mad echo I'm familiar with, and no feedback) 

[Scruffie]

Okay... well you only gave voltages for select pins on the dual opamps, can you give the full voltages U1-4.

Perhaps if C3 (47uF) or C18 (22uF) was a bit dry it might act as short grounding U1 but still pass signal for bypass... speculating there.

Your title of weirdness was certainly apt.

[honkyjonk]

Okay,

Here ya go.

U1
p1 -7.5V
p2 -7.5V
p3 -7.5V
p4 -14.9V
p5 -7.4V
p6 -7.5V
p7 -7.5V
p8 0V

U2
p1 -6.1V
p2 -3.1V
p3 -3.1V
p4 -14.9V
p5 -6.7V
p6 -6.7V
p7 -6.7V
p8 0V

U3
p1 -7.5V
p2 -7.5V
p3 -7.5V
p4 -14.9V
p5 -7.5V
p6 -7.5V
p7 -7.5V
p8 0V

U4
p1 -7.5V
p2 -7.5V
p3 -7.5V
p4 -14.9
p5 -6.9V
p6 -6.9V
p7 -6.9V
p8 0V