Looking for help with an actual vintage EHX Memory Man

[Rockhorst]

I attached the wire from the boost switch to the board, replaced the top 4558 IC and the larger electrolytics. Sure did something. I can now blend between input signal and 'whine' signal and the boost also works. Here are some fresh measurements:

Voltage at board input: 11.6 V (as before), but supply voltages on the ICs have come down to about 9.5V.

4558 closest to the jacks
Pin 1: 4.9 V
Pin 2: 4.1 V
Pin 3: 4.1 V
Pin 4: 0V

Pin 5: 4.3 V
Pin 6: 4.4 V
Pin 7: 4.4 V
Pin 8: 9.7 V (no longer equal to supply?)

4558 middle of the board
Pin 1: 3.5 V
Pin 2: 3.5 V
Pin 3: 3.5 V
Pin 4: 0V

Pin 5: 2.4 V
Pin 6: 2.4 V
Pin 7: 5.5 V
Pin 8: 9.8 V

[Scruffie]

How odd... but those voltages look a lot healthier apart from the supply of course.

You say you get 11.6 at the board input, do you mean where the supply connects because before you were measuring 12.6V there.

It's time to take readings of the SAD1024 but I'm wondering if the power supply itself is possibly to blame for the low supply, it's a high sag unit and perhaps the circuit is just putting too much load on it as that regulator style isn't that efficient, a good 18V unit might be better. For a quick test you could try two 9V batteries, or you could just replace the zener regulator set up with a 78L15.

[Rockhorst]

I'd like to keep the original regulator setup. I measure the voltage at the point where I clip it to the board. The old transformer is still attached. I was thinking that maybe, if the primary is broken but the secondary is still ok, that could be pulling down the supply because there's a lot of current flowing through the coil? I haven't noticed it heating up though.

I can connect it to a Strymon Ojai or PP2+ for 18V. Just to be double safe: I can use a 'regular' 18V supply, ground to ground and +18V to the power input?

[Scruffie]

Well if it's broken... cut the wires and test your theory

Yeah a regular 18V supply is fine.

[Rockhorst]

Well if it's broken... cut the wires and test your theory

Yeah it was just dawning on me while I was typing the post. Will test this soon, it makes sense.

[Rockhorst]

One step forward, one step back...I should've paid better attention, but when replacing the power filtering electrolytic cap I installed it with reversed polarity. On the original cap, the plus-side was marked instead of the standard minus side these days. Could've spotted that, but I blew the cap. Replaced it and the wire from the board to the switch had become detached. Fixed that. Desoldered the transformer, replaced the 4558 with a socket and installed a fresh chip.

Good news: power is now at 28V from the EHX supply to the board, 1st opamp sits at 6.7V bias, 14.6V input. So that seems fine. The clean signal is now very very faint however and most likely only induced in the wires, not really going through the switch. Probably another silly mistake somewhere.

[Scruffie]

Whoops! Oh well, you've got a good supply voltage now and that's the main thing. Why did you replace the 4558 again though?

So I'm assuming that while your clean signal is low you're not yet hearing any delay on the wet side, so the voltages for the SAD1024 and sounds like it's audio probe time to see why you're clean signal is so low and to see if signal is reaching the BBD's and passing through any of them. Pins 15 & 2 are the inputs and pins 6 & 12 are the outputs apart from the last chip where you'll want to measure the middle pin of the 1k trimmer. Looks to me the one closest to the 4047 on pin 15 is where the signal first hits them.

[Rockhorst]

The 4558 was looking good on the DMM but with no sound coming through I thought that maybe something else shorted out as that cap was losing its mind. So I decided to replace it once more with a socket (should've done that in the first place). That way, future repairs on the IC won't damage the board.

It's 1:00 AM right now. I'll continue tomorrow (vacation time, so let's hope I fix it this week).

[Rockhorst]

Necro bump, but still. I had put this unit on the shelf for a bit and haven't looked at it in a while. Took it out today and miraculously it's working. Guess my last iteration of repairs did the job but I hadn't noticed it. Doh. There's now a bypass signal and a delay signal, so the SAD chips are ok. The only thing is there's still a low volume high pitched whine riding on the audio. I'm thinking that might be due to the walwart so I'm going to look for a replacement transformer and also replace all remaining electrolytics. Any other suggestions to combat the whine?

[Scruffie]

Set delay to max, unplug the input and adjust the 1k 'balance' trim while audio probing its middle pin.

[Rockhorst]

Set delay to max, unplug the input and adjust the 1k 'balance' trim while audio probing its middle pin.

Remind me, how much am I paying you again? A 1 degree turn of that trimmer and the whine is gone.

Now to find a suitable transformer. The F-115X is not the right one since being in Europe we use 230V, not 110V. Any suggestions for a suitable replacement with the same form factor?

[Scruffie]

Set delay to max, unplug the input and adjust the 1k 'balance' trim while audio probing its middle pin.

Remind me, how much am I paying you again? A 1 degree turn of that trimmer and the whine is gone.

Didn't you get the notice  £100ph 

Now to find a suitable transformer. The F-115X is not the right one since being in Europe we use 230V, not 110V. Any suggestions for a suitable replacement with the same form factor?

That I can't help with, Maplin used to sell a match but then they went bankrupt and I'm down to my last two.

Here's the specs if it helps, let me know if you find a supplier!
12-0-12V
100mA output
Overall size: 37 x 31 x 30mm
Fixing centres: 45mm

[Rockhorst]

Considering choosing the easy way out and just installing a modern pedal jack for a wall wart.

Also have little experience reading tranformer specs. I found this one, but can't find the full specs. It seems this is 25V input, so not suitable. Right?

If I go with the wall wart option should I (re)wire anything to the center tap on the circuit board?

[Scruffie]

https://www.ebay.co.uk/itm/EI28-1W-Power-Transformer-220V-TO-6V-9V-12V-15V-18V-24V-Output-AC-Single-Dual/173371131503?hash=item285db9866f:m:mn8Bzp74VrvTThqRSuinWtw&var=472080328400

This might fit, either the dual 12 or dual 15 could be used, you'll have to measure the mounting holes etc.

[Rockhorst]

Nice find. Screw holes should be 45mm apart, sadly the ones in your link are quoted to be 42 apart. I can probably find a work around for that though. This 2W 12/15/18V one from the same seller might be a better option?