I have a grounding issue on the main input PCB
When the front silver plate grounds with the front panel of the AVT150H the signal dies? it's almost like it's totally shorting out.
I did notice however this PCB has two separate audio outputs going to the pre-amp board.
I did an experiment, I swapped the outputs on the PCB CNF1 > CNF2
and the signal was not only louder but did not disappear when grounded onto the front, I don't have a schematic for the AVT150H either, I do have a multimeter and a soldering iron, my skill level for soldering and replacing components is competent and I do have a background of SMD work too (I also own a SMD workstation)
on the small input pcb consists
4 Diodes, ZD1, ZD2, ZD3, ZD4
1 Resistor, R1
two small capacitors, C2, C3
FILT1 ? (perhaps an EMI filtration item but not sure)
one additional capacitor C1
I have replaced the input jack so far yet the problem still persists.
When the front silver plate grounds with the front panel of the AVT150H the signal dies? it's almost like it's totally shorting out.
I did notice however this PCB has two separate audio outputs going to the pre-amp board.
I did an experiment, I swapped the outputs on the PCB CNF1 > CNF2
and the signal was not only louder but did not disappear when grounded onto the front, I don't have a schematic for the AVT150H either, I do have a multimeter and a soldering iron, my skill level for soldering and replacing components is competent and I do have a background of SMD work too (I also own a SMD workstation)
on the small input pcb consists
4 Diodes, ZD1, ZD2, ZD3, ZD4
1 Resistor, R1
two small capacitors, C2, C3
FILT1 ? (perhaps an EMI filtration item but not sure)
one additional capacitor C1
I have replaced the input jack so far yet the problem still persists.
The four zeners are in series pairs, back to back. If they are not shorted, they are likely fine.
CNF1 is the signal lead, it takes the incoming signal from the jack tip and sends it down a cable to the amp input.
CNF2 is a mute line. Whenever the input jack is empty, it grounds the signal path in the OD channel to prevent noise. But it is the signal path and so can act as a weak input.
So get them right:
CNF1 connects to CNF3 on the front board.
CNF2 connects to CNF4 on the front board.
The only way I see the grounding plate on the jack affecting anything is perhaps a shorted bypass cap. C2,C3 have three legs, yes? They are effectively a wire end to end with a cap to ground in the center. If that cap sorts, then the signal path is grounded.
Pull the little jack card out, disconnect the two cables. Since the problem is signal killing, check for short condition between the two pins at each cable connector. The front plate on the jack should as far as I can see connect only to the center leg of C2 and C3 and also to ZD3. Make sure it does not have continuity to anything else.
With the amp running and the jack board still out, touch pin 1 of CNF3. Does that make hum? testing the amp function. Touching pin 1 of CNF4 should also make hum,. but only when OD channel is selected. CNF4 hum should also be weaker.
CNF1 is the signal lead, it takes the incoming signal from the jack tip and sends it down a cable to the amp input.
CNF2 is a mute line. Whenever the input jack is empty, it grounds the signal path in the OD channel to prevent noise. But it is the signal path and so can act as a weak input.
So get them right:
CNF1 connects to CNF3 on the front board.
CNF2 connects to CNF4 on the front board.
The only way I see the grounding plate on the jack affecting anything is perhaps a shorted bypass cap. C2,C3 have three legs, yes? They are effectively a wire end to end with a cap to ground in the center. If that cap sorts, then the signal path is grounded.
Pull the little jack card out, disconnect the two cables. Since the problem is signal killing, check for short condition between the two pins at each cable connector. The front plate on the jack should as far as I can see connect only to the center leg of C2 and C3 and also to ZD3. Make sure it does not have continuity to anything else.
With the amp running and the jack board still out, touch pin 1 of CNF3. Does that make hum? testing the amp function. Touching pin 1 of CNF4 should also make hum,. but only when OD channel is selected. CNF4 hum should also be weaker.
Thanks Enzo and especially for being so clear about everything.
yes that's correct, the signal path seems stronger on one than the other.
CNF2 connector when using a multimeter on continuity BEEPS when I touch pin1 and pin2 with the probes. also CNF1 pin2 is shorting with both pin1+2 on CNF2
so Pin 1 on CNF1 seems to be the only one going to ground, does this sound about right?
yes that's correct, the signal path seems stronger on one than the other.
CNF2 connector when using a multimeter on continuity BEEPS when I touch pin1 and pin2 with the probes. also CNF1 pin2 is shorting with both pin1+2 on CNF2
so Pin 1 on CNF1 seems to be the only one going to ground, does this sound about right?
Here is a link to your amp schematic:
http://bmamps.com/Schematics/marshall/marshall_avt150_avt275_[ET].pdf
CNF2 is a mute, it will show continuity unless a plug is in the jack. Plug into the jack, and the grounding contact should open the shunt across CNF2.
http://bmamps.com/Schematics/marshall/marshall_avt150_avt275_[ET].pdf
CNF2 is a mute, it will show continuity unless a plug is in the jack. Plug into the jack, and the grounding contact should open the shunt across CNF2.
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