Old Echoplex Tape Delay Problem/question

[Daniel Sorbera]

I have an old echoplex tape delay that works except for two problems.

There are two pots on the front, one labeled ECHO Sustain with the numbers 1-9 marked out. It should raise the number of repeats from 1 repeat to 9, except it stays at 1 repeat through the entire range of the pot. Does this sound like a problem with the pot, some circuitry in the delay, or a mechanical problem with the delay?

The other problem has to do with the other pot on the front labeled ECHO Volume. This pot should in theory raise the volume level of the delay through it's range. But it currently stays at a constant very quiet volume from 1-8 and just after 8 the volume of the echo gets a bit louder bit your guitar volume rolls off completely. Again does this sound like a problem I could fix by replacing the pot?

EDIT: Ok I just found a schematic and I know they are 500k pots, and I have some on hand, but I'd rather not just solder one in to see if it works because there are a good 4 wires coming off of each lug so it will be a pain.

here is a link to a schematic link

Here is a picture of it.

[pauseflash]

take an DVM and measure the resistance across the lugs of the pot as your moving it. Chances are it's a pot because of the age

[Daniel Sorbera]

Replacing the pots didn't do anything, it still only has one repeat and the same problem with the volume pot. Does anyone know what the problem might be? Or a good place/person to ask?

Another thing is the signal seems to be very quiet. The guitar sound coming through is slightly more quiet than strait into the amp but the delay sound is so faint it's hard to hear. Could it need new heads or something? It makes a squeaky sound when the tape goes around but it seems to work fine...

[Geo]

Well, I would check the wiring around the pots next.

I don't know much about solid state electronics, but I'll take a shot....

Echo sustain pot:

The "sound on sound" (SOS in schematic) switch might be the problem. If I read the diagram right, that switch turns on the multiple delays.

Echo volume pot:

It looks like the dry signal is mixed around the pot with the wet signal. There is no amplification after the pot, just the output jack. Try wiring a jumper across this pot to take it out of the circuit. If you still got problems, it's not the pot. But this....

"it currently stays at a constant very quiet volume from 1-8 and just after 8 the volume of the echo gets a bit louder bit your guitar volume rolls off completely"

... really sounds like a bad pot (one in which the wiper is breaking away from the track at full volume). But, you changed the pots. My next guess is that a transistor before that pot needs replacing.

Then there's the usual... look for cold solder joints, loose connections, burned up resistors, blown caps, etc.

Sorry I can't offer you any real advice.

[pauseflash]

Eh. I looked at the schemies finally. Check your ground on the entire thing. Both Of those controls are sharing ground, I'm assuming it's chassis ground as they are pots. Clean out around them, and take a brillow pad to where the pot sits.

Looking at your picture, it looks as though you have 2 conductor power plug on there. Change it too a 3 pronger, put ground on the chassis. Tie off the cards "Ground" to the same tie off point.

I'm sorry to say that just by looking at it, there are a few different caps and resistors, and a Transistor that could all cause that problem. As well as grounds. I suspect grounds myself, all kinds of stuff is trying to use that pot as ground me thinks, by the way the schematics look at the lugs you described.

IMHO fix the ground problem, then report back.

One more thing, check the bias adjust on that 220k pot. If you read the notes it says to adjust for max output undistorted. If that pot is shot it could at least describe the poor output. I wish I could give you the resistor number but not labeled well on this thing. Should be only trim pot inside the thing though. Assuming I'm not going crazy, those are all damn circles are the Board Terms, so it should be coming straight off Term 2.

Edited March 15, 2008 by pauseflash