Any Audio Repair Gurus Out There? McIntosh MC2500

[Puunda]

Hi All,

I'm having some problems trying to fix an MC2500. Well I'm not fixing it, a
tech is, and he's having some problems with it. The right chan 'Limit' light
comes on, although the amp is working fine. The tech has tried everything,
but is unable to find the fault.

Here is the email he sent to McIntosh

I have a MC2500 (#CS5591) in my shop for repair.

The unit works perfectly, except...the rt ch power guard limit light
illuminates at turn on. This happens with no i/p signal. Offset voltage is
2mV at 8ohm terminals. LDR1 remains off. I concluded that a faulty triac
driver, or triac could be the culprit, so replaced the lot. No change.

Next, checked all res on amp board & replaced all electros. Test: no
change. Replaced Q16 in case of leaks...no change. The voltage at Q16
collector is 9.5 v (should be 15.5v) The base of Q16 os 0V as reqd.

The reply from McIntosh was no help.

Here was another email from an experienced McIntosh repairer

Is there 15.9V on Q7 darlington that drives the Q8 triac., if no go to the
driver board and make sure Q23 the power guard driver is good, if it is good
(Q23) the darlington may be bad. The LDR uses the same drive that the PG
Driver does, if the driver fails the LDR should still work.

The Tech's reply was "Naturally I have already changed the suggested
components...to no avail"

So once again, the light is still coming on, and it looks like it's not
going to get fixed anytime soon. There are no McIntosh dealers or repairers in New Zealand, so am at a dead end.
Does anyone have any suggestions as to what might be causing this, or how to
fix it?

Any help would be appreciated.

Thanks in Advanced.

Puunda

[Netlist]

Aha, what a nice challenge.
Is the schematic available and mailable?

/Hugo

[Puunda]

Aha, what a nice challenge. Is the schematic available and mailable? /Hugo

I have a hard copy. Won't be hard for me to scan it and post it. Will do that shortly. Thanks.