Author Topic: Looking for help with an actual vintage EHX Memory Man  (Read 1058 times)

Rockhorst

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Re: Looking for help with an actual vintage EHX Memory Man
« Reply #15 on: February 25, 2019, 07:09:10 AM »
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

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Re: Looking for help with an actual vintage EHX Memory Man
« Reply #16 on: February 25, 2019, 08:13:55 AM »
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.
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Rockhorst

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Re: Looking for help with an actual vintage EHX Memory Man
« Reply #17 on: February 25, 2019, 11:25:15 AM »
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

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Re: Looking for help with an actual vintage EHX Memory Man
« Reply #18 on: February 25, 2019, 11:36:33 AM »
Well if it's broken... cut the wires and test your theory ;)

Yeah a regular 18V supply is fine.
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Rockhorst

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Re: Looking for help with an actual vintage EHX Memory Man
« Reply #19 on: February 25, 2019, 11:43:36 AM »
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

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Re: Looking for help with an actual vintage EHX Memory Man
« Reply #20 on: February 25, 2019, 04:47:38 PM »
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

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Re: Looking for help with an actual vintage EHX Memory Man
« Reply #21 on: February 25, 2019, 05:19:43 PM »
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.
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Rockhorst

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Re: Looking for help with an actual vintage EHX Memory Man
« Reply #22 on: February 25, 2019, 05:58:46 PM »
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).
« Last Edit: February 25, 2019, 06:01:01 PM by Rockhorst »