4 knob vintage EHX Memory Man issues, calibration, whine

[acobberson]

I picked up an old 4 knob DMM with the SAD1024 chips. It is the blue and red version with squelch control.

Anyway, not to beat a dead horse, but... (and I know this is talked about in other threads but I didn't find any voltage readings in the other threads.)

The issues I have are that I am getting no delay and am having some high pitch whine. I of course suspected the bias trim pots, but regardless of where I set the bias control the high pitch remains constant and I get no delay response.

Here is what I have done so far:

Level control effects overall level: working properly
Blend control goes from good signal (CCW) to no signal (CW): this suggests a problem in the delay line
checked DC voltage from power source (24V)
checked DC voltage from 2n6290         (15V)
Audio probed IC3 opamp (the one feeding into the first BBD): signal is good

Unfortunately I have no scope, so I removed all SAD1024s, then placed the first one into IC4 position. I probed the outputs and found the high pitch was there. Tried to adjust bias and gain. Obviously I can cut it out with the gain control, but not without losing signal, and like I said the bias control does nothing to affect the whine. Also, I get no delay on the outputs, so I of course suspected a bad SAD1024. So I replaced it with one of the other SAD1024s and got the same result. One by one, I put the chips back in and tested the outputs but it all remains the same. Frustrating.
However, when I adjust the delay control I do get a "warble" from the output of the BBD. This would suggest that the Delay pot is passing signal from the 4047 clock, right?

So I read voltages of the BBD chips and got what seemed to be decent readings.

(chips IC4, IC5, IC7, IC8 respectively, readings in V)

pin   voltage                           pin       voltage
1    0V (all)                             16       0V (all)
2     2.8, 5.2, 2.8, 4.4              15       4.8, 5.3, 3.5, 4.4
3     7.4 (all)                           14       7.4 (all)
4     .4, 0, .1, 0                       13       0V (all)
5     4.5, 4, 5, 4.5                   12       5.6, 5.7, 5.5, 5.3
6     4.5, 4, 5, 4.5                   11       5.6, 5.7, 5.5, 5.3
7      13.7 (all)                        10       7.4 (all)
8      7.4 (all)                          9         13.6 (all)


So my questions are:

Could a BBD chip be fried and still give decent voltage readings?
What other issues could cause loss of delay? At this point, even with the whine present I would like to confirm the BBDs are functioning.

Any ideas or insight into this is welcome!

[acobberson]

I should probably also mention that the pedal was modded from the internal transformer to DC power jack.

The DC jack GND is going to GND and the + power is wired to the positive side of the bridge rectifier.

I understand that the transformer stepped power down from 110V to 24VAC, then the bridge rectifier converted to 24VDC... so it seems these connections are correct, right?

[acobberson]

Anyone have an idea?

[marlin]

Hi,
I have the same issue with a whining unit, 4 knob version, it comes when turning up the delay to about half. Did you get further in this topic?

[Scruffie]

Hi,
I have the same issue with a whining unit, 4 knob version, it comes when turning up the delay to about half. Did you get further in this topic?

So the delay works but just whines? There's a 1k trimmer in there, unless you have a scope, probe the middle pin with an audio probe at the longest delay setting and adjust it for the least whine.

[marlin]

Hi,
I have the same issue with a whining unit, 4 knob version, it comes when turning up the delay to about half. Did you get further in this topic?

So the delay works but just whines? There's a 1k trimmer in there, unless you have a scope, probe the middle pin with an audio probe at the longest delay setting and adjust it for the least whine.

Hi and thanks, yes it works it's only the whining that is the issue. I am uncertain of which trimmer you refer to, there are 8 trimmers accessible from the back of the board. Do you know which one by hand? I attached a picture of my board, EH 1307A.

[Scruffie]

Bottom right.

[marlin]

Bottom right.

Fixed! No whine anymore and great sounding unit. Many thanks sir.

[chuckd666]

A job well done. I was going to suggest your power supply might be causing whine.

[marlin]

A job well done. I was going to suggest your power supply might be causing whine.

Hi and thanks! I actually replaced the two electrolytes in the power section for fresh ones that has the same size and look, whine was still there. What Would you suggest to improve it?