T500 - dead 16' Pedals

[tucsondave]

That pretty much narrows it down to the 16' divider. I would reflow all the solder connections on Q708, Q709 and the divider circuit pack.
If that doesn't work then replace the transistors.

td

[Jordanm]

That pretty much narrows it down to the 16' divider. I would reflow all the solder connections on Q708, Q709 and the divider circuit pack.
If that doesn't work then replace the transistors.

td

I already replaced one of those transistors with a surplus PNP from the percussion board. The numbers were different, but I was told most small signal PNP transistors would do as a replacement. I replaced Q708 because all the voltages were low (less than 1v) whereas Q709 had an increase from 0.4v to 12v from emitter to collector.

The equivalent transistors on the 8' divider seemed comparable to each other.
What replacements should I use for the transistors - I can't find any info on the existing ones. the numbers printed on them are 21132B although they all have a different letter suffix.

I might swap the divider ic's over as if the problem is with that, I should lose the 8' signal when swapped.

[tucsondave]

Those are NPN transistors. The Hammond part number 001-021132 crosses to a 2N3394 or 2N5826 (low noise).
The NTE replacement for the 5826 is NTE 123AP or NTE 199. The 2N3394 crosses to NTE 85 or NTE 289A.
NTE used to be ECG.

Don't swap parts from the 8' divider. That divider feeds the 16. You would end up with no pedals at all.

td

[Jordanm]

Ah yes,

NPN is what I meant and that's what I used as a replacement. I was only gonna swap the IC to confirm that it was or wasn't the problem. Perhaps I should just try replacing the other transistor first.

[tucsondave]

I would try the transistors first using the correct substitute part number and do both of them. They're more likely to fail than the circuit pack.

Did you have pins 11 and 12 disconnected when you checked for a tone?

td

[Jordanm]

I did have pins 11 & 12 disconnected.

Anyway, I seem to have fixed it now by replacing both the transistors. I used some obsolete NPN transistors left over from a percussion mod I did a while ago. not sure how suitable they are (think the numbers are 21133), but they work - so that's good enough for me!

I also reflowed the solder on the IC while I was there - all the joints looked good, but thought it wouldn't hurt to do.

8' and 16' tones now sound loud and clear.

Thank you ever so much for your help and I now have an ever so slightly better understand of electronics (still extremely limited though!)

Jordan