Vintage memory man op amp problem

[stratman672]

Hey guys,
I just got a vintage memory man in the mail today and I am attempting to bring it back to life. When I plugged it in there was absolutely no sound and a "pop" when the footswitch was pressed. As soon as I opened it up it seemed like someone had made a lot of alterations and did a very sloppy soldering job. Well anyways, I did an audio probe and found out that the signal only makes it to the input of the first op amp. The op amp is receiving proper voltage on both the + and - voltage pins (+-15v). This is actually the location of the circuit with the most sloppy soldering. It even had a resistor and a ceramic cap that were added on (not in the original factory schematic) and the circuit was altered with a couple traces cut! I returned everything to the original factory schematic, but the sound still stops at the op amp. could the op amp be faulty? will it have to be replaced? has anyone experience similar trouble with op amps? Any feedback would be appreciated. Thanks guys!

Note: the area in question is the A1 IC on the top left of the schematic I attached as a PDF.

[Jazz P Bass]

Op Amp

It looks like A1 is a buffered output if you connect C.
Correct?
Do you get any signal with C selected?
If not, I would suspect a bad opamp.
Can you supply an IC #?

[stratman672]

Thanks for the quick reply! :-)

Yes A1 is just a buffered output. If D is selected the pot before it acts as a dry/wet mix. Whether C or D are selected I get no signal :-( The op amp is RC4558NB.

[Jazz P Bass]

4558 opamp

I would suspect the iC is on it's back with it's legs in the air.
DOA

[Enzo]

4558s cost about three for a dollar. My labor for testing is about a dollar a minute. Let me see....

Swap the chip. if it was bad, you fixed it. If it was OK, well you are out 30 cents.

You get a pop when switching? SOunds like DC somewhere. Look at pin 1 of the A1. Got DC there? You shouldn't.

But let us move on. Set the thing up to make effect, connect it to an amp. Set your meter up for resistance and ground the black probe to the unit ground. Now with it running, touch the red meter probe to pin 1 of A2. Does that send a pop echoing along? If so, then it seems the rest of the unit might be working.

[TheEHMan]

The IC is likely dead but the parts you removed, while not on the schematic, may be improvements EH added later to the circuit. They added components to the back of many boards. I've even seen a Black Finger with nearly as many on the back as on the front.

[stratman672]

I'm ordering the equivalent 4558's on mouser. Can't hurt... they're super cheap

[stratman672]

I put in the new op amp. Still the same exact problem. Now i'm really stumped :-/

[stratman672]

CORRECTION: I forgot one connection (I feel silly). Now the effect works when bypassed. That's a step in the right direction! :-) Now I'll do an audio probe on the rest of the circuit.

[stratman672]

IT WORKS!!!! The rest was just trimpots that were VERY badly set (these memory man trim pots are a pain.) WOOHOOO I have a working memory man!!!!! :-) :-D

[Jazz P Bass]

MM

Way to go!