For sure! Not over yet I'm afraid.... Hooked amp up to some small speakers and played some music. Sounds good, but goes in protection mode when I start to push it the slightest
Use the BALANCE control to determine which channel triggers the protection, then search for defective components.
Good Luck!
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Good advice! Something strange is going on with the balance. It actually doesn't work. Only hear a slight change in tone when used. Source direct gives a boost in volume, witch I can't say I have heard before. Maybe there's nothing wrong with main amp board.
No difference in left or right balance in regards to protection mode either - still triggers with volume increase
No difference in left or right balance in regards to protection mode either - still triggers with volume increase
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Did some digging and pulling on solder joints, and found bad traces on P851 power board. I can not believe how poor the quality on the PCB's are on this thing - they are like dry biscuits. Several joints can be lightly pulled and copper tracing just cracks and whole joint comes off. Fixed several on main amp board but starting to believe this amp has done its duty....
True. I'll see, but being so bad these boards are I don't think it will last and could pose a risk of damaging other gear.
I reckoned since balance did not work and source direct acted funny, and bypass actually bypasses the whole tone control and balance board and protection mode still trips, maybe there is a unstable power issue or something. 18V rail goes thru all these boards fed from power board so I figured there might be something there. One trace/joint on Q856 witch are connected to 18V rail was really bad
Does the protection trigger when you adjust the volume control with no input signal? i.e. disconnect/short circuit input (don't use the PHONO input for testing) + SPEAKERS A & B switches OFF.
Good Luck!
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I have not tried with shorted input, but it does not go in protection with volume up and no signal
If you are still going on try alternately disconnecting one of the input channels phono plugs say left and then right to see if either/both channels trigger protection on there own .
I assume protection is still triggering with the speakers disconnected .
Double check that all the output trannies are conducting by measuring the bias over each individual 0.18ohm ceramic resistor/element .
I have more things you can check but need the feedback first .
I assume protection is still triggering with the speakers disconnected .
Double check that all the output trannies are conducting by measuring the bias over each individual 0.18ohm ceramic resistor/element .
I have more things you can check but need the feedback first .
I've a PM80II on my desk right in this moment, too... @TO: Check the two 330µF/63V Cerafine at P851... Mine were cooked and showed 1,1 and 1,5 Ohms ESR (!). Replaced them with 330µF/80V Nichicon UBX 150°C-types. They would last longer than the whole amp now... Also check every (!) solderjoint on P851... They're horrible... Some of the 1 Ohms-resistors on P851 were out of range, too. If they are imbalanced you could get some offset, too.
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Thanks for further advice. I think a thorough check on P851 needs to be done as I've suspected something going on there. Just to clarify, I have redone every single solder joint on all boards, but the quality on the traces is very poor, so several are vey brittle and crack easy. Espescially around where heat builds up.
When I find the time I will do this, and get back with feedback on behavior. I noticed one thing though - when playing music and protection mode kicks in, it seems like the power indicator LED's on P701 is kinda pulsating in tune with the music/beat and faint audible noise from somewhere inside the amp following the beat
When I find the time I will do this, and get back with feedback on behavior. I noticed one thing though - when playing music and protection mode kicks in, it seems like the power indicator LED's on P701 is kinda pulsating in tune with the music/beat and faint audible noise from somewhere inside the amp following the beat
I have a feeling it all points back to P851. If this board is wonky it would affect all circuits, maybe other than power output circuitry (?) Should be possible to measure some rail voltages when amp goes in protection mode
Check the diodes and continuity between diodes on P851 and also the bridge rectifier on P801 maybe a rail is down to half wave rectification instead of full .
I emphasise "maybe" , yes a scope can be useful but like you say would it be used enough .