Discussion in 'Pioneer Audio' started by rmunson, Dec 21, 2017.
scratchiness almost eliminated -- which is good....
I don't want to jinx it... scratchiness seems to have been resolved after cleaning relay....
but if scratchiness is not resolved will continue troubleshooting with recommendations above --
Thanks for all of the help with this --
Good to hear you have it sorted .
ok - well after a little more than a week of normal operation the krispy krackle sound has come back -
it's only on the right channel -
I've seen a lot of references to replacing transistors on the power amp and protection circuit boards --
For the 727, on which board would the group recommend starting? Is there any further troubleshooting I can do to isolate the source of the problem?
Thanks guys --
Thanks Oldsansui441 -
do I have the input differential pair correctly id'd?
So basically - get to this board and desolder these transistors and replace with KSA992 - you referred to mirrors - what would those be on the service manual schem below?
Thanks for your help!
diff pairs would be most likely . a scope would help but multi-meter should suffice .or simply change them .
i myself might hit them up with freeze spray .
Thanks Pete -
and do I have the diff pairs correctly ID?
What are the current mirrors referred to earlier?
Diff pairs are correctly ID'ed. When you install them get the flat faces facing each other and allow the heads to touch. A very small dab of heatsink grease on the flat faces and tie them together with Heatshrink tubing. This helps with the temperature tracking (evens it out between the pair).
A mirrored pair would be a NPN with it's corresponding PNP opposite. The output's are mirrored pairs as are the drivers. I'm not sure what quaddriver is referring to as current mirrors...........
wondering if maybe my relay is the source of the problems - the cracklepop is intermittent - I am hearing the speakers "whumfph" on startup now - which would be an indication that the relay is not doing its thing any longer, right? -- I'll test this a bit more and verify that the system is powering up without the relay opening and the signal is going straight to the speakers.
is it worth disabling/defeating the relay? or should I really try to replace it if it's faulty?
there should be a delay with relay click at power on
Rmunson. The relay only does what it's told to do or not do by the protection board. Suggest you take power supply readings and make sure they are all OK per spec 1st. Once that's done and or corrected, rebuild the Protection board with all new caps and transistors. There is a Tr/C network that controls the timing of the relay to close 4 to 7 seconds after power on. PIONEER used an early(AWM-011) or late protection board (AWM-027). Your Model type and Serial # will decide on which to use. The Supplemental manual that covers this is here......http://www.kallhovde.com/pioneer/sx-727supp.pdf. Rebuild accordingly, and test.
ok -- thanks for this recommendation -
yeah - the speakers whump immediately on power on - so there is something not happening on the protection board - I will investigate the protection board and observe the relay more closely....
If I decide to start replacing components on the board, will I need to completely extract the board, or is there enough play with the connecting wires to allow me to gently lift the board up and get at the underside?
Hmm, definitely sounds like the relay is staying closed at all times which is odd, normally when that circuit has problems it is the opposite scenario but great advice from Larry about checking supply voltages then looking at protection board components.
I haven't worked on a 727 but with other Pioneer's there is usually enough room in wires when removed from loom clamps to gently pivot board over to access parts.
no click at all says 2 things .. relay circuits been hacked . relay contacts stuck together ,
thanks guys -
so I'm in there and making readings on the protection unit board -
are voltage measurements in DC unless indicated AC?
yes you got it . or it will be obvious after looking at schematic .. everything after rectifiers is dc .
ok - well, I'm getting some readings - nothing crazy off the charts different... attached is my annotated schem -- my measurements in red
anyone see anything particularly concerning? any other measurements I should try to get on this board?
looking good here after i worked out to open in new tab to reduce size .
Good morning guys -
continuing to do initial diagnostics with my 727 -
I have measured voltages on the power supply board and power amp board - nothing seems dramatically out of spec, but would appreciate comments - my measurements are in red
images are hosted here
one thing I'm observing while running the system -
the snap crackle pop symptom does not occur when cover is off -- so possibly the issue is heat related? The power supply card does have some visible heat browning by the big resistor.
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