Reticon SAD1024 BBD troubleshooting question

[12Bass]

Years ago I built Radio Shack's Archer Electronic Reverb project (277-132), which included a Reticon SAD1024.  Although the end result of this particular effect was underwhelming, I've always wanted a good sounding flanger and have decided to build the A/DA flanger using the old SAD1024.  However, I'm not sure that the BBD chip is working properly....

In the old Electronic Reverb, I'm able to get signal at the output with careful adjustment of the bias trimpots.  As I sweep the bias adjustment it will be clean and loud for an instant, then fade into a quieter distorted signal.   However, I can't seem to get the adjustment to stay at a point where the output is clean.  This leaves me wondering if the SAD1024 chip might be failing, or perhaps if some of the almost 30 year old electrolytic capacitors or diodes might be the problem.  Given their present scarcity and expense, I'd rather not have to purchase another Reticon. 

So, I'm wondering if others here might have some experience with the SAD1024, particularly with its failure modes.  Does it usually fail completely, partially, or  

Thanks!

[theehman]

Delay ICs usually either work or not, no in-betweens.  It's possible the bias trimpot is the problem.

[12Bass]

Delay ICs usually either work or not, no in-betweens.  It's possible the bias trimpot is the problem.

Thanks for the reply!

I swapped a couple of the trimpots onboard and it didn't make any difference.  Hopefully it is some of the other components that have failed.

[Mark Hammer]

There will often be an electrolytic cap on the bias trimpot.  make sure that one is a keeper, too.

[StephenGiles]

Here's where I usually come in - it could be a problem with the clock circuitry as no BBD will work properly if it is not receiving decent clock signals, could you post the schematic perhaps?

[Mark Hammer]

You know, a person could make a living out of offering a "BBD testing service".

"Send me your BBD and $10.  I will test it under real world conditions in an EHX Electric Mistress, Boss CE2 chorus, Deluxe Memory Man, Boss CE-1 Chorus Ensemble, or MXR Analog Delay, confirm functionality status, and mail it back to you in a static-free envelope."

I'm NOT offering such a service.  I'm just saying that for the number of people who find themselves in a quandry with a pricey chip in a vintage pedal and don't know how to verify whether it is fried or not, a person could make some spare change on the side.

[oldschoolanalog]

http://www.pmerecords.com/Docs/Archer_Electronic_Reverb.pdf
Schematic on page 15.

[theehman]

You know, a person could make a living out of offering a "BBD testing service".

"Send me your BBD and $10.  I will test it under real world conditions in an EHX Electric Mistress, Boss CE2 chorus, Deluxe Memory Man, Boss CE-1 Chorus Ensemble, or MXR Analog Delay, confirm functionality status, and mail it back to you in a static-free envelope."

I'm NOT offering such a service.  I'm just saying that for the number of people who find themselves in a quandry with a pricey chip in a vintage pedal and don't know how to verify whether it is fried or not, a person could make some spare change on the side.

There's my new side business!  I'd do it!

[12Bass]

Here's the schematic:



R42 is the trimpot which seems to be causing the most trouble (i.e. it is the one which won't stay set where the BBD output is clean).  I already swapped R43 with R42, and replaced C14 and C9 and IC5, and it didn't make any difference. 

Thanks for all of the help!

[12Bass]

Thankfully, my recent A/DA flanger clone build has shown that the SAD1024A is fine.  However, I was worried for a while because the flanger was exhibiting similar behavior to the Electronic Reverb - BBD bias adjustment was impossible.  Thanks go out to oldschoolanalog for helping me track down a bad trace on my homemade PCB.  Once that was repaired, the old girl started flanging like a whirlwind!