Some struggeling with a defect Zapco Z100MVX mono. I have schematics from a 2-channel Z100, but this one has some differences.
Amp came in with leaky filter caps, and 3 other small leaky caps. Replaced them, also the railcaps. Cleaned the board very good om both sides.
It powered on, green led, but no output. DC offset about 40mV.
railvoltages +/-37V.
On the opamps +/- 15V.
Current idle 1A (low i think...?)
Traced the signals, and on all the opamps it seems normal, but (as far as I'm can follow the tracks on the pcb) does not enter amp differential / drivers.
Muting jfets are in (J110) but the muting circuitry differ from the Z100 2-channel.
Maybe there is a schematic somewhere.??..it will help me a lot.
Amp came in with leaky filter caps, and 3 other small leaky caps. Replaced them, also the railcaps. Cleaned the board very good om both sides.
It powered on, green led, but no output. DC offset about 40mV.
railvoltages +/-37V.
On the opamps +/- 15V.
Current idle 1A (low i think...?)
Traced the signals, and on all the opamps it seems normal, but (as far as I'm can follow the tracks on the pcb) does not enter amp differential / drivers.
Muting jfets are in (J110) but the muting circuitry differ from the Z100 2-channel.
Maybe there is a schematic somewhere.??..it will help me a lot.
Photo's of the board
Attachments
Last edited:
Hi Bert,
Too get a more clear view of the defect for myself, I struggled with a same problem a while ago.
When you follow the trace from the RCA's, where does it stop?
Does the RCA signal get to the "input" of the switches?
Does the RCA signal get to the "output" of the switches?
if it doesn't maybe you have a broken switch
Does the RCA signal reach the OP-amps?
If it does reach the OP-amps, does the OP-amp outputs a amplified signal?
If not check if your op-amp, VCC or GND is correct when your op-amp does receive a signal.
If your op-amps doesn't receive a signal, check your potentiometers and switches.
Too get a more clear view of the defect for myself, I struggled with a same problem a while ago.
When you follow the trace from the RCA's, where does it stop?
Does the RCA signal get to the "input" of the switches?
Does the RCA signal get to the "output" of the switches?
if it doesn't maybe you have a broken switch
Does the RCA signal reach the OP-amps?
If it does reach the OP-amps, does the OP-amp outputs a amplified signal?
If not check if your op-amp, VCC or GND is correct when your op-amp does receive a signal.
If your op-amps doesn't receive a signal, check your potentiometers and switches.
Hi, I have measured with a scope the inputs and outputs of the opamps. Switches are ok (0 ohm or infinite), I only have some distorted signal on the 5532 dual opamp, the other TL074 are inputs/ouputs ok. Gain adjust works.
So i think I remove the J110 jfets (muting?) and then the 5532.
Root cause could be the electrolite from the leaky caps, sometimes via's or traces are damaged. Difficult to see with this board...or just a defective opamp. We'll see...
So i think I remove the J110 jfets (muting?) and then the 5532.
Root cause could be the electrolite from the leaky caps, sometimes via's or traces are damaged. Difficult to see with this board...or just a defective opamp. We'll see...
After some weeks I got the schematic from Zapco. With that i could trace the fault back to the muting circuit. C10 4,7uF/16V had some electrolite from the other leaky caps underneat. After replacing C8/ C9 /C10 capacitors and cleaning the pcb, the amp works again.