Roland SDE-2000 repair help needed

[kekke]

Hello everyone

I inherited a broken Roland SDE-2000 rack delay but it has been a hell of a quest to fix and I need some help to track the fault in the delay line.

First of all there was a short on the -15V rail and it kept blowing the 2x 400mA fuses (F1 and F2). I was able to locate the short and it was because of a tantalum capacitor that failed and went conductive C39 to be exact. First time encountering this! It seems it is definitely time to replace them! Couldn't believe my eyes tbh.

I replaced all tantalum caps in the unit after this and the unit boots good now and the bypass and direct signal are working. All led's come up, input level meter is working and the display can be set by the delay time buttons.

At the voltage regulators, +15V, -15V, +5V, -5V and 12V are present.

However no DELAY line sound.

i started audio probing trying to see how far I get signal.

At TP1 I get a good clear audio signal so up until there everything is good.

Then the 4066 and compander...

I put a new CD4066BE with socket to cancel that one out. I get audio at the inputs of the 4066, I get a good signal before R79, after it is very attenuated going to the LM311 and at the D/A converter it's very faint, I feel it is too faint to be good.

At the compander the NE570, I get good signal input at pin 2, 3. No signal on pin 15, 14 and 16.

No signal at all at IC8, IC7 seems fine.

All help welcome, because I am a bit lost in troubleshooting at the 4066 and compander going in the D/A converter.

The schematic is here: LINK

[g1]

I don't see pins 7 or 10 of IC6 (NE570) so are they hiding somewhere?

[kekke]

It seems they are not in use and not connected.
I think the expander side of the NE570 has failed. Normally audio should appear at pins 14,15. Or I could try taking the FET Q32 out and see if audio appears?

[g1]

According to the block diagram on pg.4, IC6A is on the input side of the A/D and IC6B is on the output side. So Q32 will not be making a difference if the problem already exists going in to the A/D.
When you said the signal was weak going in to A/D, did you mean pin 18 or 19 ?

[kekke]

Hi gi1, pin 19 of the D/A has very faint audio for a short while with my audio probe (3s or so).

After R79 -> going in the D/A converter and to the LM311, the signal is very faint.

R79 = a 3k series resistor and after there are two diodes anti parallel. D23,24, in circuit they seem to measure OK. I socketed the LM311, (no replacement at hand yet).
I did test without LM311 and I get very faint audio, so same problem.

I am also following along the lines of the block diagram to not miss something.
In the block diagram, there is a switch SW5A that chooses between two LPF filters.
In both situations I get audio to the TP1, so the switch passes audio (just to verify).

The compressor side of the NE570 seems to work at IC7 I get audio, but at the exapander side the problems begin.
I checked electrolytics around the NE570, C55, C56, they work and charge.

So at NE570 pin 14,15. I get absolute silence.

Replaced compander NE570
Replaced IC5 4558 at IO to D/A pin 18
Replaced IC7 4558 at compander side
Replaced IC8 4558 at expander side
Replaced IC5 ==> I get 0V Vref at pin 14,15 all good.

My main suspects is still 4066, the original is a Hitachi 14066BP, which I replaced with TI CD4066BE. I hope it's not a case of "picky IC's".
Next suspect the LM311 not doing it's work on the D/A converter (SET/RESET) control.

Going to scope at pin 18, 19 to see what I get there exactly. More suggestions?