Maxon AD900 (4) MN3008 repair troubleshoot help

[snarblinge]

Have been asked to repair one of these, suspected incorrect adapter.

Reverse polarity Diode looked a tiny bit warm, everything else seems ok.

replaced diode.

no effect, just clean,

Im getting voltage happily all over the board but would appreciate some guide as to what to look for where. Anyone have one?

with most pedals i'd be replacing stuff here and there to get it up and running, but I don't have a bunch of Mn3008s lying around.

what should I be getting on the ins and outs of the MNs?

Thanks in advance.

[armdnrdy]

Use an audio probe to trace the signal. This will help you zero in on the problem area.

http://www.diystompboxes.com/pedals/debug.html

You can find the schematic for the 4 MN3008 version here:
http://www.diystompboxes.com/smfforum/index.php?topic=109774.0

[ElectricDruid]

If you've got an oscilloscope, you could check the clock signals on pins 2 and 6 of each delay line too. If the clocks have died, even good BBDs would do nothing.

Tom

[snarblinge]

Thank you both,

armdnrdy, found the schematic, thanks, your build was inspiring, if i have to buy more of these things i'm tempted to build one myself.

Druid, there is an oscilloscope shaped hole in my collection of things, and thats really why I was asking. I no longer work where they are readily available, i'll seek one out.

[ElectricDruid]

In the absence of an oscilloscope, you could use a CMOS ripple counter to get the clock frequency down to audio frequencies. If you used a 7-stage counter (say), you'd easily have enough octaves that you could hear what was going on with the clock. Or find a 'scope-equipped friend!

HTH,
Tom

[snarblinge]

Scope located....

[ElectricDruid]

Ah, much the better option. Good luck.

T.