The 15V both + and - rails should definitely hold up longer than the relays keep the speakers connected.
It seems odd that they are collapsing so quickly as the current drawn from them is usually quite low.
As has already been muted, I would replace the caps in the 15V supply chain, both pre and post reg.
It seems odd that they are collapsing so quickly as the current drawn from them is usually quite low.
As has already been muted, I would replace the caps in the 15V supply chain, both pre and post reg.
Was looking closer at the card mountings in the amp and saw that Q5 transistor did not have an isolation pad between it and the heatsink ... every other transistor has one. I cut a piece of paper (thickness of a matchbook cover) and slid it underneath the transistor. Buzz is very faint now.
Another weird thing is the "thump" intensity has become very random after this. Every time I switch the amp on now I'm get a different turn off thump characteristic. ... soft "poof" to large "crack" and in between.
I measured the offsets again to see if this has any correlation:
Channel ---- SGL ---- Bridged
1 ------------3.7mV-----16.8mV (1&2)
2 ------------3.5mV------^^^^^^^
3 ------------3.3mV-----16.9mV (3&4)
4 ------------3.8mV------^^^^^^^
5 ------------4.6mV-----17.7mV (5&6)
6 ------------3.2mV------^^^^^^^
Thump consistency:
Bridged Mode
(1-2) med to soft "poof"
(3-4) softest to med "poof"
(5-6) med "poof" to larger "crack"
^ all are varying now but this is representative (average) "thump" output.
All are without any input load.
Individually ... they all range in intensity depending on ??? (each switch ON-OFF seems either softer or louder now)
Another weird thing is the "thump" intensity has become very random after this. Every time I switch the amp on now I'm get a different turn off thump characteristic. ... soft "poof" to large "crack" and in between.
I measured the offsets again to see if this has any correlation:
Channel ---- SGL ---- Bridged
1 ------------3.7mV-----16.8mV (1&2)
2 ------------3.5mV------^^^^^^^
3 ------------3.3mV-----16.9mV (3&4)
4 ------------3.8mV------^^^^^^^
5 ------------4.6mV-----17.7mV (5&6)
6 ------------3.2mV------^^^^^^^
Thump consistency:
Bridged Mode
(1-2) med to soft "poof"
(3-4) softest to med "poof"
(5-6) med "poof" to larger "crack"
^ all are varying now but this is representative (average) "thump" output.
All are without any input load.
Individually ... they all range in intensity depending on ??? (each switch ON-OFF seems either softer or louder now)
Puppet Q5 it is a plastic transistor. I would not worry about it. One question. Does the amplifier boards are plug in like the PC I/O boards? Can you remove them without unsolder wires? I think that amplifier it is well constructed. Another thing can you read the +/- 15 with the voltmeter in the AC selector.
-15V (read on AC) = .820V
+15V (read on AC) = OL swing ... 71.8V .... OL .... 71.8V .... OL ....71.8 (1/2 second sweeps back and forth)
Cards are sort of like that except the pins are not on PCB as say a PCI card (connector soldered with pins 90'ed out and then down, on amp card ... buss card has female connectors for each amp cards pins ... buss card has pins (just like on the amp cards) at one end soldered to PWR module)
+15V (read on AC) = OL swing ... 71.8V .... OL .... 71.8V .... OL ....71.8 (1/2 second sweeps back and forth)
Cards are sort of like that except the pins are not on PCB as say a PCI card (connector soldered with pins 90'ed out and then down, on amp card ... buss card has female connectors for each amp cards pins ... buss card has pins (just like on the amp cards) at one end soldered to PWR module)
I would change all the electrolytic capacitors since you have to remove the board. For this test if you want just change C43, C44, C49, C50. Yes you can check the other power supplies using the AC. Normally that is the first thing that I do. Check the DC power supply voltages in the AC mode. Normally if you check a battery in AC it would read zero volts. What are you doing in the amplifier power supplies is rectifying the AC to DC pulsating and then by adding the capacitors you smooth it to be almost at close to be a battery DC. The closed to zero the better. So if you read the DC voltages in AC it would let you know how good it is since it should read zero for good a rectified voltage. Hoped this would clarified what are you doing when reading the voltages in AC mode.
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