Sunking - Incorrect Voltages

[ichilton]

Hi,

I'm just finishing up building a single sided Sunking board someone etched for me.

I've got the switch, dc socket and jacks connected, but not the pots or clipping diodes yet - but I thought i'd fire it up and check the voltages against the ones in the document.

Most of mine are in the same kind of ball park, except the following:

- Instead of 0, I get some mV readings.

- Instead of 18v, i seem to be getting 12v

- I don't seem to get the negative voltages.

Here are all of my readings:

Supply: 8.52v

IC1:
1: 4.26v
2: 4.26v
3: 3.17v
4: 1.6mV
5: 4.26v
6: 4.26v
7: 4.26v
8: 8.53v

IC2:
1: 4.43v
2: 4.28v
3: 4.26v
4: 84mV
5: 4.25v
6: 4.27v
7: 4.11v
8: 12.29v

IC3:
1: 8.53v
2: 2.5v
3: 3mV
4: 2.5mV
5: 83.8mV
6: 3.08v
7: 6.71v
8: 8.51v

Please could someone who understands what they are and should be tell me what's going on?

Any idea what the problem is with the ones which are out?

Will the variance in the others affect the sound in anyway, or is it just down to component tolerance and that my 9v supply seems to be a bit lower than the documented ones?

Thanks!

Ian

[madbean]

What kind of charge pump have you used?

Couple things that could cause what I'm seeing: D5 is backwards or dead, C19 is backwards or dead.

Maybe a pic of the top/bottom?

[ichilton]

Charge pump is a ICL7660SCPA from:
http://www.ebay.co.uk/itm/251066447875

Thanks for the suggestions! - i'll check those out tonight!!

Ian

[ichilton]

Oh!!

I just looked up what D5 and C19 are.

I've not fitted D4/D5 yet as I thought they were just for clipping and the circuit would be unaffected without them? (i'm going to have them switchable with some different types but thought it would be fine without it and just like CompCut on the FD2).

I guess that's my problem then!

I'll fit some diodes in there tonight and check the voltages again.

Thanks,

Ian

[madbean]

Wait, my bad. I forgot the component naming is different. D4/D5 are clipping diodes on the ETCHED Sunking layout. D1 and D2 are for the charge pump. IIRC, they are different because I redrew the schematic for the FABBED v3 Sunking.

Sorry for the confusion.

[ichilton]

Ah, right! - that makes more sense. I'll check D1 & D2.

I assume therefore that C19 refers to the fabbed one and it's C21 (off pin-4 of IC3) that I need to check?

Thanks!

Ian

[ichilton]

ok, those capacitors and diodes look ok, but I did find (and fix) a solder bridge on one of the capacitors near there!

The supply now seems to have gone up to 9.19v and i'm getting the following readings:

IC1:
1: 4.58v
2: 4.59v
3: 3.36v
4: 0.2mV
5: 4.55v
6: 4.57v
7: 4.57v
8: 9.19v

IC2:
1: 5.04v
2: 4.59v
3: 4.58v
4: -8.83v
5: 4.57v
6: 4.57v
7: 4.15v
8: 16.84v

IC3:
1: 9.19v
2: 4.61v
3: 0.4mV
4: -4.38v
5: -8.20v
6: 4.03v
7: 7.09v
8: 9.18v

How do those look?

Thanks,

Ian

[madbean]

Yup, that looks good!

[ichilton]

Cool, thank you!

Is the 0.2 and 0.4mV is ok instead of 0v then? - that doesn't indicate a short?

Is the variance between mine and yours just due to the supply and component tolerances then?

Will I hear a difference in sound because of the different voltages?

Thanks!

Ian