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 the'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.
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.

Yung

Puunda wrote:
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.


I'm not sure. But honestly if you are paying someone else to fix your
amp it is quite unfair to ask that he be tutored for free! I am sure
that McIntosh can fix your amp (probably by board swap so the whole
chassis need not be sent in) or if not that there are talented EEs he,
or you, could hire for a consulting fee. There are many out of work you
know.

If this were a DIY hobby project and I knew, I'd tell you. My guess is
that unless you can fully backwards engineer the circuit from the
schematic you are going to have to very painstakingly shotgun it (no,
not blast it with a 12-gauge, replace parts and redo connections) or
compare a lot of voltages and resistances to a working unit if one can
be borrowed.

"Puunda" wrote in message
...
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.


crossposts removed.

i have a suggestion that many will regard as a smartass remark but is
serious.

cut the peak limit light out of the circuit.

it wont come on. it wont bother you. the amp works fine. the other light
works fine. it will tell you is you are overdriving if your ears are not up
to the task. just kick back, relax, and put on some Eagles music.

I have considered that, and the tech has suggested that. However as he said,
if it DOES somehow get a fault in that chan (a real one), then I'll never
know. That plus the fact it wouldn't look too good if I were to sell it.
Plus it's just annoying that you've paid this much $$$ for a 'reliable' Mc,
and am paying a tech to 'fix' it.

I'll see how I go in a few more weeks, but if nothing happens, then I will
just take it back and listen to The Eagles.

"TimPerry" wrote in message
...


crossposts removed.

i have a suggestion that many will regard as a smartass remark but is
serious.

cut the peak limit light out of the circuit.

it wont come on. it wont bother you. the amp works fine. the other light
works fine. it will tell you is you are overdriving if your ears are not
up
to the task. just kick back, relax, and put on some Eagles music.

"Puunda" wrote in message
news
I have considered that, and the tech has suggested that. However as he
said,
if it DOES somehow get a fault in that chan (a real one), then I'll never
know.

baloney: that's like saying if you car stops you wont know anything is wrong
unless a dashboard idiot light is on


That plus the fact it wouldn't look too good if I were to sell it.

why sell? this should last the rest of your natural life

Plus it's just annoying that you've paid this much $$$ for a 'reliable'
Mc,
and am paying a tech to 'fix' it.

the peak lights on amps come in handy on PA systems. if you are turning up
to the point of clipping at home you are going to have some hearing loss to
contend with.


I'll see how I go in a few more weeks, but if nothing happens, then I will
just take it back and listen to The Eagles.

take it easy.... not to the limit one more time


"TimPerry" wrote in message
...


crossposts removed.

i have a suggestion that many will regard as a smartass remark but is
serious.

cut the peak limit light out of the circuit.

it wont come on. it wont bother you. the amp works fine. the other light
works fine. it will tell you is you are overdriving if your ears are not
up
to the task. just kick back, relax, and put on some Eagles music.

I have considered that, and the tech has suggested that. However as he
said,
if it DOES somehow get a fault in that chan (a real one), then I'll
never
know.

baloney: that's like saying if you car stops you wont know anything is
wrong
unless a dashboard idiot light is on

Sometimes you can't (until it's too late), which is why they do have so many
lights. If the limit light comes on only comes on when it's clipping, then
you're right, there's not much use. But there's not really much use for pin
stripes on cars, or that shiny stuff on tyres, but it's part of the package.
Like red paint make cars go faster.


That plus the fact it wouldn't look too good if I were to sell it.

why sell? this should last the rest of your natural life
I had a 66 Mustang covertible which I never thought I'd sell. I had a 62
Selmar Paris Saxophone which I thought I'd never sell, but I had to sell
both. Just can't predict the future. Plus I've got my eyes set on the
MC2600. 100W more power, lower distortion, better SNR, and has balanced as
well.

Yung