ok i have on the bench a CARVER PM 1200.
This unit was on use since the 1990 in a cafeteria.
Very good unit good sound simple with not much ic and fancy systems.
So when all ask me what to buy from second hand or from ebay i suggest to by this mid 90s
amplifiers because is very simple on troubleshooting and fix.
So the main problem was that one channel no sound.
All the transistor are ok.
The power supply are all there(+/- 124,+/-76,+/-36,+/-11,).
Why so much voltages?Because use a magnetic field power supply and depend on a simple triac circuit
to change the voltages under load.Very simple use 3 power supplys (High mid low) to feed the speakers.
Also the unit have thermal protection after the transformer,dc protection(no relays simple transistor
circuit) and overvoltage protect using a ic comparator.
The ic comparator takes 5v from regulator 12v and another 5v coming from +124v supply.
This circuit save the unit. When 124v goes up the ic triggers and close Q2 Q4 with a diode.
The unit shut down.
As you can see in the photo something is blow big time.
The one emitter resistor R87 5W missing also R30,R63 gone R85,R86 R47,R49 survived R48 open D19 ok R62 R32
out of specs.Al the 1n4004 ok.All MJI trans ok.
If was another ampl nothing of this would survive even the ouput trans.
Now what happen is that the unit have be not calibrated overheat or simple drifting specs.
The owner dont giving me details ,perhaps the unit have fall down when it works or the enviroment have a lot mains noise or vibrations.
In the unit have a filter cup failure due to excessive ripple curent so they put 2 2200μF 50V in series.
The unit not calibrated start consume a lot of curent until the Q18 and Q19 who sense the voltage limit unable to work and the
Q26 who monitor the current to R49 triggers and passing a shutdown signal through C30 to power supply.
So the overload protection do the work.
Carver said to calibrate the unit cold but i see that when heats the number goes up so 10min should be okay with no load .
On no signal you have about 30Watt idle when is full more that 500w .
Service manual at http://thecarversite.com/shell2.htm
I cant upload because size.
This unit was on use since the 1990 in a cafeteria.
Very good unit good sound simple with not much ic and fancy systems.
So when all ask me what to buy from second hand or from ebay i suggest to by this mid 90s
amplifiers because is very simple on troubleshooting and fix.
So the main problem was that one channel no sound.
All the transistor are ok.
The power supply are all there(+/- 124,+/-76,+/-36,+/-11,).
Why so much voltages?Because use a magnetic field power supply and depend on a simple triac circuit
to change the voltages under load.Very simple use 3 power supplys (High mid low) to feed the speakers.
Also the unit have thermal protection after the transformer,dc protection(no relays simple transistor
circuit) and overvoltage protect using a ic comparator.
The ic comparator takes 5v from regulator 12v and another 5v coming from +124v supply.
This circuit save the unit. When 124v goes up the ic triggers and close Q2 Q4 with a diode.
The unit shut down.
As you can see in the photo something is blow big time.
The one emitter resistor R87 5W missing also R30,R63 gone R85,R86 R47,R49 survived R48 open D19 ok R62 R32
out of specs.Al the 1n4004 ok.All MJI trans ok.
If was another ampl nothing of this would survive even the ouput trans.
Now what happen is that the unit have be not calibrated overheat or simple drifting specs.
The owner dont giving me details ,perhaps the unit have fall down when it works or the enviroment have a lot mains noise or vibrations.
In the unit have a filter cup failure due to excessive ripple curent so they put 2 2200μF 50V in series.
The unit not calibrated start consume a lot of curent until the Q18 and Q19 who sense the voltage limit unable to work and the
Q26 who monitor the current to R49 triggers and passing a shutdown signal through C30 to power supply.
So the overload protection do the work.
Carver said to calibrate the unit cold but i see that when heats the number goes up so 10min should be okay with no load .
On no signal you have about 30Watt idle when is full more that 500w .
Service manual at http://thecarversite.com/shell2.htm
I cant upload because size.
Attached Files