Servicing a 90's EH Deluxe Memory Man

DrNomis · Post by **DrNomis** » 17 Aug 2018, 07:52

Hey Everyone,

I've got a 90's reissue EH Deluxe Memory Man pedal that I'm in the process of trying to get working properly for a local Darwin musician, this one is displaying some pretty weird symptoms:

* When first connected up to an amp, plugpack adaptor, and guitar, the pedal seems to work normally, producing the usual chorus, vibrato, and delay effects.

* When the footswitch is used to bypass and then engage the pedal, it no longer produces those effects, just a clean, un-effected sound, the bypass led is lit (pedal engaged), and the overload led lights when the guitar is strummed harder.

* Disconnecting the plugpack from the pedal, and then plugging it back in gets the pedal working normally again.

How's that for a weird one?, I don't think it's the footswitch since I've checked it and it is good.......

Manfred · Post by **Manfred** » 17 Aug 2018, 08:41

Maybe the weird behaviour is due to mechanical load while pushing the stomp switch.
To investigate this, shake and press the enclosure when the pedal functioning properly.

DrNomis · Post by **DrNomis** » 17 Aug 2018, 08:59

Cheers, I'll give that a go, but it's a bit unlikely, the footswitch does seem to be working as it is supposed to, the pedal I'm working on has four MN3008 BBD chips in it, I don't think any of them could be faulty since that would result in the pedal not producing any delay, chorus, or vibrato effects.

i can get the pedal to work normally, and then not-normally, by alternately stomping on the footswitch and disconnecting/plugging in the plugpack.

Here's a couple of pics of the Deluxe Memory Man I'm working on:

Intripped · Post by **Intripped** » 17 Aug 2018, 10:16

hi Doc,
i don't know what's causing this strange behaviour, but for sure i would start investigating the power supply section.
try and measure voltages when the pedal is not working properly.

it could also be the quad op-amp (...it's a quad opamp, isn't it?)

edit: ok, it's not a quad opamp. maybe NE570.

Manfred · Post by **Manfred** » 17 Aug 2018, 10:22

Is the circuit diagram available?
Is the imprint of the fifth IC blacked out?

DrNomis · Post by **DrNomis** » 17 Aug 2018, 10:34

Manfred wrote:Is the circuit diagram available?
Is the imprint of the fifth IC blacked out?

I did manage to find a circuit diagram for the EH Deluxe Memory Man, but it has MN3005 BBD chips on it, whereas the pedal I'm working on has MN3008 BBD chips in it, that fifth IC is an NE571 IC (it actually says SA571 on it).

I'm going to try removing the circuit board from the case so I can have a close look at the underside using a magnifying glass, and see if there's anything that could cause the problem.

Got the circuit board out of the case and it's actually a 2007 vintage EH Deluxe Memory Man reissue.

Intripped · Post by **Intripped** » 17 Aug 2018, 10:59

DrNomis wrote: I'm going to try removing the circuit board from the case so I can have a close look at the underside using a magnifying glass, and see if there's anything that could cause the problem.

yes

while the effect is on, connected to amplifier and guitar, and malfunctioning, try also to touch (with a plastic stick or something, in order to avoid shorts) all the components, and see if something happens: sometimes, expecially on SMD boards, a broken solder joint is very hard to detect, even with a magnifying glass.

DrNomis · Post by **DrNomis** » 17 Aug 2018, 11:24

Hmmmmm....I found two solder pads associated with a board-mounted power diode, labelled as D2 (IN4003), both of the solder pads look like they didn't get enough solder, I can see light shining through one of them if I hold the board up to the light, surely the cause of the problem can't be as simple as that?.....

Intripped · Post by **Intripped** » 17 Aug 2018, 17:37

any news?

...since the NE570 (or SA571) is commonly used in delay pedals, maybe you have one around; it would be a simple test to try and sub it (it's socketed if i'm not wrong)

DrNomis · Post by **DrNomis** » 18 Aug 2018, 06:00

Intripped wrote:any news?

...since the NE570 (or SA571) is commonly used in delay pedals, maybe you have one around; it would be a simple test to try and sub it (it's socketed if i'm not wrong)

Not yet, I'm going to try doing a bit of signal-tracing with a scope today, and see what I can find out, I'm interested in seeing what the signals on the CD4047 chip are doing, if I am reading the circuit diagram right, the CD4047 chip is supplying the Clock signal to at least two of the MN3008 BBD chips, I want to see if those signals are disappearing when the pedal is bypassed, that would explain the weird behavior if my theory is correct.

DrNomis · Post by **DrNomis** » 18 Aug 2018, 07:07

Okay, checking the signals on the pins of the CD4047 chip with the scope indicates that it is un-affected by the footswitch when it is used to bypass the pedal.

DrNomis · Post by **DrNomis** » 18 Aug 2018, 08:24

Okay, so looking at the clock signals on pins 2 and 6 of the four MN3008 BBD chips with the scope reveals something interesting, I'm getting a reasonably good clock signal on pin 2 of each of the MN3008 chips, but, on pin 6 of each MN3008 chip the clock signal is much lower in level, and, it looks like a roughly full-wave rectified sine-wave....wondering if that's normal, since I've looked at another Deluxe Memory Man schematic that shows pin 11 of the CD4047 clock chip tied to pin 6 of each of the MN3008 chips, I've checked the signal on the CD4047 clock chip and it looks good there, with a decent signal level, next thing I tried was to use the continuity test function of my multimeter to check for continuity between two pins labeled CLK on the small daughter board that has all the MN308 chips on it, and pins 2 and 6 of each MN3008 chip, I noticed that there's continuity from one of the CLK pins and each of the MN3008's pin 2, but the other CLK pin shows no continuity for each of the MN308's pin 6, so it looks like each of the MN3088 BBD chips is only getting one clean clock signal when they should really be getting two......

.....

Here's the schematic I'm using to trace out the clock signals that are supposed to be going from the CD4047 IC to pins 2 and 6 on each of the MN3008 BBD chips:

P.S. Thanks and appreciation goes out to uncleboko for finding it for me....cheers!!!!

DrNomis · Post by **DrNomis** » 18 Aug 2018, 09:17

Okay, I'm thinking that the reason why the clock signal from the CD4047 chip isn't getting to pin 6 on each of the four MN3008 chips when it should be, according to the circuit diagram, is because of a possible open circuited PCB track on the back of the small daughter board that has the four MN3008 chips soldered to it, they are all in IC sockets, I need to completely de-solder the daughter board from the main PCB to have a close look at the underside of the daughter board.

Oh!!!......silly me....I just had a look at the datasheet for the MN3008 IC, and what I thought was pin 6 on the MN3008 was actually pin 3....

So, when I put the tip of the scope probe on pin 6 we do indeed see a good clock signal.

DrNomis · Post by **DrNomis** » 18 Aug 2018, 12:13

Okay, now it's not producing any effects whatsoever, regardless of whether it is bypassed or not, I just get a clean un-effected signal, but according to what I see on the scope screen, the four MN3008 ICs are operating like they're supposed to.....

.....

Going to leave it for now and come back to it tomorrow.

Intripped · Post by **Intripped** » 19 Aug 2018, 00:07

If i understand correctly, the four BBDs are working, and 4047 too.
so the problem should be located after the last mn3008: i would use an audio probe on the following components.

...

maybe it's the switching relay

Edit: probably there's no switching relay on your board (I was looking at the schematic).

DrNomis · Post by **DrNomis** » 19 Aug 2018, 04:55

Intripped wrote:If i understand correctly, the four BBDs are working, and 4047 too.
so the problem should be located after the last mn3008: i would use an audio probe on the following components.

... maybe it's the switching relay

Edit: probably there's no switching relay on your board (I was looking at the schematic).

Yep, the one I'm working on doesn't have a relay for the footswitching, and as far as I can tell, the CD4047 and all four of the MN3008 chips appear to be working normally, I just can't seem to figure out why no delay, chorus, and vibrato effects are being produced when the pedal is engaged, the only controls that seem to be doing something are the Blend and Level controls.

uncleboko · Post by **uncleboko** » 19 Aug 2018, 07:56

May be stating the obvious but have you tried disconnecting the switching altogether and testing the wet path for audio at various points?

DrNomis · Post by **DrNomis** » 19 Aug 2018, 10:55

Here's a close up pic of the revision number for the Deluxe Memory Man I'm working on: