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Flanger Issue 2 pcb query
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author Flanger Issue 2 pcb query
Pav
Hi, Despite my concerns about shakey hands and smd components in another thread, I overcame these and pretty pleased so far with the smd work on the flanger ..albeit not tested.

Im now bemused to find C61 and C59 have 3 holes in pcb for a polyester (wima) cap that has two pins. for example C17-C20 are all marked up as 2 pin caps..but not C61 the same value.

The schematic shows just two connections. The picture on the product page show wima like caps in those positions on an issue 2 pcb

Im surprised elJay and leverkusen who have built flangers did not remark on this. Perhaps they knew how to resolve.

Should I have purchased a different type of capacitor hmmm..... ?
Synthbuilder
The middle holes are vias and are not connected to the capacitors' leads. Either leave them alone or fill them with a bit of solder once you have finished populating the board.

There's quite a lot of vias on this board as it's the only way to get connections from the top layer of the board where the surface mount components reside to the other three copper layers.

Tony
Pav
thanks. I did think it might be via but thought it best to ask as I had never come across that layout before. Had seen a via under an ic socket though.but saw that these middle holes had tracks to Smd caps so my addled brain wanted some reassurance.

Should be ready to test tomorrow. nanners
Pav
For the record ..first test of flanger failed....so I'm into debugging phase.

I had patched input to an oscillator and dly out to mixer. Without power I can hear dry audio showing there's a passive path from in to out. Switch power on that audio disappears. No led action with drive either.

Power to board is checked ok.
Comms to sock6 continuity checked ok.
Voltage at pin5 of 3207s showing 8.8volts.
No smoke or overheating. Nothing.

I had already checked polarity of Smd diodes in situ and zeners using dmm diode test mode.

So I'm now down to checking soldering of EDIT...just found a solder bridge. END EDIT?
I'm off to examine the schematic , but if there are suggestions as to how to narrow the search radius I'll take them.
Pav
so far corrected solder bridge and also resoldered suspect pin8 on U17.
all tl072s appear to have correct vdd vss except U11 which appears to have -11.11v instead of +15 - though im not sure it was a solid reading. so ill re check.

Would it be fair to say i can ignore decoupling caps from the initial search as they would not deliver a complete failure.?
Synthbuilder
Do you have a scope?

Do you have the dry output from the mix output? If not that may indicate that the fault is relatively simple. It's a pretty short path for the audio signal to go from in to out. Check that you have an audio signal at pin 5 of U14. A simple home made audio probe is useful if you don't have a scope.

If there is a signal at pin 5. Check that the same signal is heard at pin 7 of U14. It should also be present at U15 pin 1 and pin 7.

Tony
Synthbuilder
Pav wrote:
Would it be fair to say i can ignore decoupling caps from the initial search as they would not deliver a complete failure.?

Yes. There are more likely problems to find first.

Tony
Pav
Hi i have scope ... status is I have dry signal to mix out socket now - and U15 is in that .

The signal reaches U9 pin2 , pin 1 c28 pin1 R30 . the output on pin1 through to "limiter" is either nil or a dc offset. does that sound right?

limiter out leads to bbds pin3 ins... so

As i type im struggling to find the piece of schematic that follows on from "dry mix" label as signal sould continue somewhere too. EDIT ok that leads to U15 so thats ok ... so I think U9 is damaged.
Synthbuilder
Pav wrote:
The signal reaches U9 pin2 , pin 1 c28 pin1 R30 .

That's a problem. There should be no signal present on pin 2 of U9. It's wired as a summing amplifier and pin 2 is a virtual earth, ie. the voltage should be very close to 0V.

So I think U9's pin 3 is not soldered to its pad.

Tony
Pav
Im confused sorry. Schematic shows the audio in signal from U14 pin7 through R43 into pin2 of U9 with pin3 connected to ground. Ok If pin2 becomes a virtual ground, then where should i measure the signal next ? I presumed pin1 of U9 to see the triangle i injected, given zero feedback.

EDIT
I reflowed pin 4 which looked like it was hanging..and voila I have signal on pin1 of U9 ...good on to find the next problem as no instant joy.
Pav
just taking a break - i now have signal through to U6p3
I need to reflow now to get a signal from U12 p7 to R18 and on to U7.

Ill then check the clocks..one looks ok @340Khz the other is showing 110Kz but this could be noise... ill keep u posted.
Synthbuilder
Pav wrote:
Schematic shows the audio in signal from U14 pin7 through R43 into pin2 of U9 with pin3 connected to ground.

R43, along with the actions of the U9, turns the signal into a current proportional to the signal voltage. Your scope only measures voltage so it appears as if the signal has gone but it hasn't.

Quote:
I reflowed pin 4 which looked like it was hanging..and voila I have signal on pin1 of U9 ...good on to find the next problem as no instant joy.

If you have one unsoldered joint there may be others. Before you go probing around any further, go grab a magnifying glass and look at all the IC pins to make sure they are making good contact with the PCB. Sometimes an unsoldered joint will work because it is in physical contact with the board only to fail later when the board is flexed or the solder pad tarnishes.

Tony
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