Mini mu build issue

[peterd237]

Finished the VFE Mini Mu up last night and I've got some problems, basically it just sounds horrible. Very little going on in down mode, and just a slight quack in up mode, but if you hit a chord is just distorts in a really nasty way. Went over the parts and I believe I have everything in the right place. (One point of confusion for me though was the jump indicated to the right of the optocouplers marked as R28 on some of the docs. Since the photo of the completed box in the docs shows a jump I think that is correct, but guess I should confirm)
Checking voltages showed a problem though, and I would appreciate any help I can get with this. I won't be able to post picks until late this evening.
OPA134
1  8.38
2  0
3  0
4 -8.13
5  0
6  0
7  8.18
8 ignored

LM358
1  7.39
2  2.21
3  4.29
4  -8.14
5  8mV
6  9.9mV
7  436mV
8  8.65

TLE2074
4   8.65
11 -8.15
(all others zero)

[jimilee]

Got some pictures and are your options oriented correctly?


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[peterd237]

By options, do you mean optocouplers?  Then yes, I verified they are correct (gotta love autocorrect)   Will be able to post pictures later this evening

[jimilee]

By options, do you mean optocouplers?  Then yes, I verified they are correct (gotta love autocorrect)   Will be able to post pictures later this evening

Stupid auto correct, sorry about that.


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[peterd237]

here are the pics

[peterd237]

the other side

[madbean]

here are the pics

The top optocoupler appears to be backwards based on the NSL imprint on the casing (its facing opposite the one below it).

[peterd237]

Hadn't noticed that. The dot is what i was going by, but looking at them the printing on the side on the lower one is on the opposite side of the dot, but the top one the dot is right in the middle of the printing. I'll switch it around  see what happens.

[peterd237]

Well not much improvement. Sounds marginally better, and voltages still off on OPA134 (unchanged) and LM358 (pin 2 now reading -.03 all other unchanged).  Is there anyway to test the optocoupler? it's obviously misprinted, but can I just assume its bad?

[Betty Wont]

here are the pics

The top optocoupler appears to be backwards based on the NSL imprint on the casing (its facing opposite the one below it).

The NSL imprint can go either way and doesn't seem to be related to the LED orientation inside the part. Go by the painted dot. I have a batch of these from small bear and the imprints are random.

[peterd237]

Thanks, that good to know. I will be pulling them both this evening to test just to be sure, but it looks like they might not be the problem after all.

[peterd237]

Both optocouplers tested ok. Unless someone sees something else, I guess I need to step through it with an audio probe.

[peterd237]

finally was able to get back to this. First thing I did was pull the ICs and put in sockets (was too impatient and didn't have them on hand when I started it) .  There was no improvement. Started tracing with an audio probe and had no signal on R1, so moved back to the 'in' on the audio board and also had no signal. Checked the 'out' on the audio board and there was the signal. Checked the switch board and the signal was on the  'out' terminal and not on the 'in' terminal here as well.  I'm totally confused at this point

[jimilee]

Are you sure you're plugging into the in and not the out.


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[peterd237]

Well...i did say I was totally confused