Debugging a Keeley 4 knob Compressor (aka Ross with extra pots)

[alex_spaceman]

So, put this one together and having no luck in getting it to work. No sound at all. I used Mark's layout.

Had a round of probing with the DMM and here are the readings...

IC
1-0.12
2-0.14
3-3.86
4-0.00
5-0.12
6-6.89
7-9.02 (same as provided by the psu)
8-8.29 (does this voltage come from the IC? the pin itself is NC..?)

   Q1      Q2      Q3      Q4      Q5
E   6.61      6.20      0      0      8.44
B   1.50      6.90      0      0      7.90
C   2.33      6.20      8      8      9


So, yeah... looks pretty weird to me, but not 100% sure on what voltages I should be looking for. Does anyone have the desired voltages for comparison? That would help me hugely to understand what might be wrong/where to look for cold joints/micro bridges/faulty components/general faults and mistakes.

Any input is much appreciated, so a big thank in advance to any of you who might be of help!

Alex

[R O Tiree]

Pin 2 of the IC should be the same as pin 3. Q1 and Q2 are out to lunch as well.

Here are some pretty standard Ross voltages. It doesn't matter much if they're a bit out from these values, as long as, for example, the relationship between B and E is right on the transistors.  Plug the guitar in but turn the volume right down.  Set Sustain to 5 o'clock (max) and Vol to about 12 o'clock.

IC1

1.   NC
2.   4.6
3.   4.6
4.   0.0
5.   0.7
6.   2.7
7.   9.0
8.   NC

Q1

C  6.6
B  2.8
E  2.2

Q2

C  6.9
B  2.7 (connected directly to pin 6 of IC1)
E  2.1

Q3

C  8.9
B  0.0
E  0.0

Q4 same as Q3.  They are not conducting at the moment, as there's no input signal, so these figures are to be expected.

Q5

C  9.0
B  8.9
E  8.4

[alex_spaceman]

Thanks a lot Mike, will have a good look around each of the non matching pin!

[alex_spaceman]

So, the voltages led me to realizing I'd miss the link between rows 3 and 4, but I'm still not getting life out of it and the voltage for pin 6 and Q2 B is still too high. Q5 still gives lower readings than it should.

Here's a couple photos in case they might help:
http://dl.dropbox.com/u/65506935/k4kc_up.JPG
http://dl.dropbox.com/u/65506935/k4kc_down.JPG

Thanks in advance!

[R O Tiree]

Alex, I've added some markers to your pics.

http://dl.dropbox.com/u/91341319/Image1.jpg On this one, possible bad joints are ringed in light blue and a possible solder bridge is ringed in red.

http://dl.dropbox.com/u/91341319/Image2.jpg On this pic, I've marked the 220k resistor in red.  This should be further over to the right and there should be a jumper in that position.  The 2n2 cap to its left should only have a 0.1" pin spacing - the box cap you have in there has a 0.2" spacing - did you bend the leads to make the correct connections?  The green ring shows where you have joined 2 resistors together down the same hole... Don't know quite what's going on there?  If you meant to join 2 lower-value resistors together in series to make a bigger one, you need to make the join in "free air" above the board, not soldered to the copper side, where they're going to make connections that shouldn't be there.  Lastly, the light blue ring shows where you're missing a jumper.

On Mark's layout, some of the jumpers make several connections - they're denoted by the little blue rings with white dots in the middle and there's a warning about watching for double links in single holes under the right hand diagram.  Are those extra connections made?

This is not an exhaustive list... it's 01:00 and I have to go to work in 6 hours, so you'll have to forgive me for not checking every component position/spacing and their correlations to the solder side, which I would have attempted had I had more time.  Once you've made the corrections and checks outlined above, I suggest you go through the board, item by item, ticking off each leg of each component in turn, having checked and re-checked its proper position on Mark's layout.

[alex_spaceman]

Hey Mike, thanks a lot for your contribution, much appreciated.

Went through all the joints and there doesn't seem to be any bad ones. Checked them all and applied a bit of extra solder to all of them, but nothing has changed, still a silent pedal and a few wrong readings...

The reason why my build looks different is because I actually used the layout which includes the trimpot, but replaced the trimpot with two 1k resistors when I realized I didn't have presets that would fit. Basically I put a 1k resistor between where lugs 1 and 2 of the trimpot would have been and one where 2 and 3 would have been.

I bent the legs of the 2n2 and it joins on rows 2 and 3, by the points where the pot is wired.

Lastly, the missing jumper between rows 3 and 4 had been added since, which fixed the voltage at pin 2, but that's about it...

Thinking about doing the whole thing again as it's doing my head in, but don't have enough tantalums for it. Might socket electros instead and/or take them from this dud board. Hopefully a bit of extra desoldering/soldering won't do them much harm.

[R O Tiree]

Ahhh... The other build. All I can say is that it was 01:00 - sorry.

Did you check the multiple connections on those 2 long jumpers at the right hand side of the board?

I suggest we go through this thing in sequence... Have a really close look around Q1 and see if you can get that one behaving itself as a starter for 10.

New pics and new voltages?