jsteiger

Hello,

I built my LC25 a month back or so. Haven't turned it on in a little while because i've been busy with vacation and life.  It was working totally normal last time I used it, but for some reason the unit is not passing any audio anymore. When I bypass the unit, audio goes through, but once I switch it to active, nothing. I've tried different slots in my box to no avail. I do not have a spare DOA sitting around, should building another DOA and tossing it in be the first step?

Thanks,
Adam
Is your opamp fully seated?
http://capi-gear.com/catalog/DOA_Install.php
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jsteiger

Well, if its not the opamp it could be a bad/cold solder joint somewhere. If things were working fine and then stopped, that's usually the case.
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Well, if its not the opamp it could be a bad/cold solder joint somewhere. If things were working fine and then stopped, that's usually the case.

 I mean I had it on and working for probably 20 or so hours  so it wasn’t just a brief thing.  I’ll order up an op amp today and see if that doesn’t sort it out if not I guess I’ll have to start searching the board for other issues 😐

Hey Jeff,

Ordered a new 2520 and 1731 to see if the op amp helped. My unit is now working, but the 1731 has a very considerable amount less of headroom (something like 8db) before noticeable saturation. Is the normal or do you think I botched something on the 1731? Either way, I'm happy that the unit is working again!

jsteiger

Hey Jeff,

Ordered a new 2520 and 1731 to see if the op amp helped. My unit is now working, but the 1731 has a very considerable amount less of headroom (something like 8db) before noticeable saturation. Is the normal or do you think I botched something on the 1731? Either way, I'm happy that the unit is working again!
This is way not normal. There should be zero difference in headroom between properly built discrete opamps.
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This is way not normal. There should be zero difference in headroom between properly built discrete opamps.

Oops! Reversed the Q7 and Q8. Thanks Jeff!

The 5kHz gyrator is comprised of GR21, GR22, GR24, GC15 and GC16. Also half of A4 which is shared with 2.5kHz. If that is fine I would ASSume the chip is fine.

Hi Jeff,
I resoldered all of the resistors and caps listed above, as well as each point on the 5k knob, and the problem still exists... i might get a dB or two boost or cut at 5k with the knob FULLY cranked. I’m wondering if I should replace the two caps GC15 and GC16? Thoughts?
Thanks again for your time!
Chris

jsteiger

Hi Jeff,
I resoldered all of the resistors and caps listed above, as well as each point on the 5k knob, and the problem still exists... i might get a dB or two boost or cut at 5k with the knob FULLY cranked. I’m wondering if I should replace the two caps GC15 and GC16? Thoughts?
Thanks again for your time!
Chris
Post a pic of that section of the PCB. I wanna check and see that the R's are placed correctly.
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Post a pic of that section of the PCB. I wanna check and see that the R's are placed correctly.

see the photo below.
Thanks Jeff.
- Chris


jsteiger

see the photo below.
Thanks Jeff.
- Chris
Looks like you have GR14 and GR22 mixed up.
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