I ran across an MRV-1505 that has a weird power-on issue.
I have never ran across one of these before. So, first thing I did was check the outputs, and power supply transistors. All good.
But, it did not power on.
I removed the power supply board, and saw a trace that had blown apart nearby the remote accessory connection. I patched that up, and attempted to power up the board with all the plugs disconnected.
The power supply came on and ran fine.
So I reconnected all the plugs, and once again, had no power. Not making any sense to me.
So, I noticed if I unplugged CH505 connector in the middle of the power amplifier board, the power supply would come on! Soon as I reconnected that connector, the power supply would shut down.
Then eventually after trying to test that connector for voltages, I plugged it back in and now the power supply is staying on...
what??
Anyone run into this before?
I have never ran across one of these before. So, first thing I did was check the outputs, and power supply transistors. All good.
But, it did not power on.
I removed the power supply board, and saw a trace that had blown apart nearby the remote accessory connection. I patched that up, and attempted to power up the board with all the plugs disconnected.
The power supply came on and ran fine.
So I reconnected all the plugs, and once again, had no power. Not making any sense to me.
So, I noticed if I unplugged CH505 connector in the middle of the power amplifier board, the power supply would come on! Soon as I reconnected that connector, the power supply would shut down.
Then eventually after trying to test that connector for voltages, I plugged it back in and now the power supply is staying on...
what??
Anyone run into this before?
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Does the amp now produce full power clean audio on both channels?
If you push on various parts of the boards, does the amp ever shut down?
If you push on various parts of the boards, does the amp ever shut down?
I have not done an audio check yet, No...
Flexing the PCBs was one of the first thing I did to rule out bad connections, and it did not change the behavior.
Flexing the PCBs was one of the first thing I did to rule out bad connections, and it did not change the behavior.
If it does it again, power up through a limiter to see if it will power up without completely shutting down to see if you can see a fault (high voltage across the source resistors, problems with the regulators...).
Yea, it has not done it again.
But, I do not have sound out of one of the channels UNLESS I flip the switch to input 1+2. Stereo and Mono give me no sound on one channel, but has sound on the other.
I also have to have the Phase to 180. if its 0, No sound on one channel even with 1+2 set.
I cleaned out the switches with contact cleaner because the working channel was noisy and cutting in and out when touching the switches.
But, I do not have sound out of one of the channels UNLESS I flip the switch to input 1+2. Stereo and Mono give me no sound on one channel, but has sound on the other.
I also have to have the Phase to 180. if its 0, No sound on one channel even with 1+2 set.
I cleaned out the switches with contact cleaner because the working channel was noisy and cutting in and out when touching the switches.
yea I have that, saw it in another thread. the switch layout is confusing to follow in the schematic, because it doesnt indicate which sections short together.
Map out only the good channel signals with the switches in the position where the other channel doesn't have output. Then feed the other channel and see where the signal is lost.
ok i will do that.
I found a bunch of broken solder connections on the potentiometer PCB, so I fixed all that, sadly no change in behavior.
Also one of the switches if I touch it, it just static and cuts in/out. I tried spraying the switches multiple times and it isnt fixing it, I think they are just bad...
the Phase 0/180 switch, I have to hold it in the middle between the two positions to get sound on both channels. otherwise I don't.
Any idea where to get replacement switches?
I found a bunch of broken solder connections on the potentiometer PCB, so I fixed all that, sadly no change in behavior.
Also one of the switches if I touch it, it just static and cuts in/out. I tried spraying the switches multiple times and it isnt fixing it, I think they are just bad...
the Phase 0/180 switch, I have to hold it in the middle between the two positions to get sound on both channels. otherwise I don't.
Any idea where to get replacement switches?
If you have steady hands, you may be able to disassemble them, clean the contacts (600-1200 grit sandpaper or a fiberglass scratch pen), tighten the contacts, lubricate then reassemble.
It may be difficult to find the switches but someone like PacParts or even ebay may have some NOS available.
It may be difficult to find the switches but someone like PacParts or even ebay may have some NOS available.
If you find generic replacements, post the part numbers and brand so that others will benefit.
I've only found a tiny minority of switches (not counting those that were physically damaged) that could not be cleaned. The only ones that I commonly replaced were those in SS amps and that's because the originals were readily available.
I've only found a tiny minority of switches (not counting those that were physically damaged) that could not be cleaned. The only ones that I commonly replaced were those in SS amps and that's because the originals were readily available.
I did pull the switches apart and clean them. that fixed the issue in 1 channel.
Turns out the issue is more severe. I found that all the op-amps in that specific channel had no rail voltage. so the +/-15V is missing on that channel only.
Followed it back, the two zener diodes are shorted, and the two power transistors are open.
Now, I measured the +/-15V of the op-amp section to ground, I have shorts in the op-amps too.
So something happened which blew out the regulator, and probably blew out all the op-amps in that channel...
Fun times.
Turns out the issue is more severe. I found that all the op-amps in that specific channel had no rail voltage. so the +/-15V is missing on that channel only.
Followed it back, the two zener diodes are shorted, and the two power transistors are open.
Now, I measured the +/-15V of the op-amp section to ground, I have shorts in the op-amps too.
So something happened which blew out the regulator, and probably blew out all the op-amps in that channel...
Fun times.
Ok so I have the amplifier working again, both channels after replacing the op-amps, the 15V regulator zener diodes and transistors, and did a ton of resoldering on some bad/broken connections.
Both channels work perfect, and sound strong. BUT... I still have that CH505 issue. if I unplug it, amp powers up. soon as I plug it back in while hot, it quits. shuts down.
Sometimes after its running for a bit, I can plug CH505 back in and it doesnt shut down. But if I power down, it wont come back on.
Its very bizarre. i tried heating up the caps to see if it was a capacitor issue, behavior doesnt change.
Both channels work perfect, and sound strong. BUT... I still have that CH505 issue. if I unplug it, amp powers up. soon as I plug it back in while hot, it quits. shuts down.
Sometimes after its running for a bit, I can plug CH505 back in and it doesnt shut down. But if I power down, it wont come back on.
Its very bizarre. i tried heating up the caps to see if it was a capacitor issue, behavior doesnt change.
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Actually, there is a break between the primary and secondary grounds somewhere. if I ground the RCAs to the Power supply ground, everything comes on and works fine.
the CH505 is on the primary ground, while most of the amp is on the secondary ground.
But according to the schematics, they show connected together somewhere. Problem is, I dont know where?
the CH505 is on the primary ground, while most of the amp is on the secondary ground.
But according to the schematics, they show connected together somewhere. Problem is, I dont know where?
If the DC offset protection is referenced to the primary ground, a floating secondary (floating shields) could cause the fault.
The 1507 must have grounded shields to prevent showing a fault.
I'm sure that you've already done this but for others, measuring the voltage on that connector, when the amp is working normally and not, then comparing the voltages may tell you precisely where to look.
The 1507 must have grounded shields to prevent showing a fault.
I'm sure that you've already done this but for others, measuring the voltage on that connector, when the amp is working normally and not, then comparing the voltages may tell you precisely where to look.