C84 U1, U3, and J3, pin 2 to U1, U3, pin 8 voltage questions

[billkahler]

Step 36 page 17 of the assembly instructions mentions U2 - does this actually mean U3? (Maybe U2 was a trademark infringement. . . .) I don't have a U2 silkscreened on my board or in my BOM.

Voltages at U1 and U3, pin 8 are 11.6 on both of them and they cycle through some values for a few seconds before settling on 11.6. Also, I do have sockets in these spots if that matters.

U1 and U3 pin 4 are both -14.

I checked diodes and caps mentioned in step 37 and all are correct. I did have trouble with Q5 - had the wrong value and replaced it with the correct value and it's not as clean as Q6, 12, and 13 - still looks like it's making a good connection.

Thanks for the help.

[billkahler]

Been working on this - no luck yet.

Rechecked soldering etc.

For U1 and U 3 I was getting about -14 at pin 4 but pin 8 was still reading 11.6 I decided to try adjusting R68 and R72 until I got 14 at pn 8 but then pin 4 was -18.

Any ideas as to what to check next?

[tpryan]

Step 36 page 17 of the assembly instructions mentions U2 - does this actually mean U3?

Yes, corrected instructions are up now.

For U1 and U 3 I was getting about -14 at pin 4 but pin 8 was still reading 11.6 I decided to try adjusting R68 and R72 until I got 14 at pn 8 but then pin 4 was -18.

Are you saying you can't adjust R68 to get +18v? Are you sure that R68 and R72 are both 1K pots (marked 102)? Have you got the right values in R69 and R70? Is U4 noticeably warmer than U5?

[billkahler]

R68, R72, R69, R70 values are correct.
U4 seems to be a little warmer than U5, but not much, and really not what I would call hot at all.

I have adjusted R68 and R72 and I'm getting volatges of
pin 4, -23.56
pin 8, 18.94
on both U1 and U2.

Should I move on? I was assuming the pin4/pin8 values should be +18, -18.

Thanks for the help.

[dkatz42]

Should I move on? I was assuming the pin4/pin8 values should be +18, -18.

The values should be +- 18; adjust the negative supply (whichever pot it is) to bring that back down to -18 and you'll be golden.

[billkahler]

Thanks for that dkatz.

Voltages are reading 18.06 at pin 4 and -18.08 at pin 8. Do they need to be exact?

I think my problem may have been adjusting R72 too far counter clockwise. Doooh!

[dkatz42]

That's about as close as you're going to get it (and probably within the accuracy of your DMM.)