Hi, I have just made the last solder for my A15MK2, and tested it with a speaker. Channel 1 is working and sounds good, but channel 2 is dead. I have measured the voltages at the power supply board and found the following:
At rectifier (+): 300 V (should be 298, OK!)
At C28 (+) 292 V (should be 290, OK!)
At C26 (+) 200 V (Should be 262, Not OK!)
Does anyone have any ideas where to start looking? Is it likely to be a fault on the power board, or on the main board/tube sockets?
BR /Mike, newbie ???
A15MK2 only Channel 1 works
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Hi Mike,
the pretty low voltage at C26 means, that the current through R48 is higher than it should be. Please check the voltage at
1) R29 (between both sides) => should be about 5V
2) R10 (between both sides) => should be about 8V
When voltage 1) is much higher, something with tube V2 (or the circuit around it) is wrong, if voltage 2) is much higher, it's V1 (which is not likely because channel 1 works), when both voltages are roughly OK, it's V3 (or V4, which is also unlikely, because the phase inverter works with channel 1). Please measure and post also the voltages at C17, C10, C8.
Regards,
Martin -
Hi Martin, many thanks for the support! I have measured the points you specified, and here are the result:
Over R29: 115 V (!)
Over R10: 4 V
At C17 (+): 115 V
At C10 (+): 0
At C8 (+): 110 V
So if that indicates something wrong with V2, I will go trough all wiring and components there once again. If you get any more ideas based on the values I will be very grateful!
BR /Mikael -
OK, this was a bit embarrasing... one leg of R29 was touching the ground bar! I'm gonna do some more testing now, but the first voltages seem to be OK now.
Thanks alot for guiding me to the starting point for thr trouble shooting!
BR //Mike -
Hi Mike,
that's good to hear. I hope, everything works fine now.
Regards,
Martin
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