Roland re201 echo problem

[pontiacpete]

This one looks great. I've cleaned and demag-ed the heads, sprayed out pots and jacks.
Everything seems to works well but only for about 30 seconds. Then the echo dies out. Then there's a little bit of distortion. The echo can sometimes be heard for a while more by hitting very hard on an instrument.
The reverb works.
This doesn't seem like a tape issue but what do I know.
Maybe a failing component like a leaky cap.
Here's the schematic,
Does anyone have a idea where I should start?

I'll post some voltages soon.

[The Dude]

Do you have new tape? I've seen this problem before with really old tape. After you clean the heads and everything looks good, you then run old tape across them and the oxidation from the tape gunks them up again right away. Many of these machines have old if not original tape loops still residing inside them. Check to see if your heads are all brown again after you run the machine for a bit.

[pontiacpete]

The heads are not getting brown after running it a while.
I'll order some more loops and see if that helps
Thanks Dude

[Mick Bailey]

If hitting it makes a difference I would suspect a mechanical problem somewhere, rather than a leaky cap. Try the chopstick method to see if you can pinpoint what is being disturbed if you hit the unit. It could be a fractured resistor or bad joint. You also need to compare your DC voltages with the schematic to make sure a voltage isn't dropping - could be a connection to the PSU going high resistance. Take a look at your tape path to ensure your tape isn't running out of alignment.

The schematic has test voltages and scope signals. If you have a scope - fine. If not I'd recommend rigging up an audio probe and trace the signal through the stages fed from the heads. You should be able to pick up the signal directly from the playback heads on tag 17 and follow it through as per the marked voltages on the schematic. It would be useful if you could input a square wave of 1khz @ 2.4mv RMS to give a baseline for testing. And a new tape.

A quick test of an audio circuit is to check the 'hot' side of any pots that handle audio (tone control/volume etc) as well as the wiper to see if a signal gets that far. Try to narrow the fault down to a block and then look for a failed component or problem within that block.

[pontiacpete]

Mick, thanks for your helpful suggestions. I will give them a go, since i have time before the loops shows up.
I did try chop sticking around the board with no signs of problems.
I will try the putting a square wave and also check the pots as you say.
thanks
pete

[pontiacpete]

Installed the new tape loop and the echo works.
Thanks for the great help. Much appreciated!