I have the red board kx650.4 with no audio no visual signs of damage. Other than two 5R resistors R368, R468 we're burnt in the output section. I replaced them only to still not have audio passing to the speaker terminals. I been at it for two days without positive result. Could use some help.
Attachments
Until better help arrives...
Have you confirmed that you have all power supply voltages (rail and regulated)?
Have you followed the signal to the main board to see if the preamp section is working?
Have you confirmed that you have all power supply voltages (rail and regulated)?
Have you followed the signal to the main board to see if the preamp section is working?
FYI, R168,R288,R368,R468 should be 4.7 ohm, and are part of the output filter along with C142,242,342,442-104/M caps. It was quite common for these resistors to fail, and for a time we would upgrade to 2 watt I believe. I don't recall what caused this, but is not related to the no audio problem.
Once you have the measurements and signal traced the preamp board it should be fairly evident. Be sure to measure the DC voltages around J11 using speaker ground for the black probe. Along with the obvious no Rails or Regulated voltages, a failed muting circuit, bad solder or through connection on the header socker-J11. It's also possible that R73-470 ohm resistor is open or high. Check the RCA's and REMJ1-remote gain control for broken or bent pins shorted to adjacent pins.
Once you have the measurements and signal traced the preamp board it should be fairly evident. Be sure to measure the DC voltages around J11 using speaker ground for the black probe. Along with the obvious no Rails or Regulated voltages, a failed muting circuit, bad solder or through connection on the header socker-J11. It's also possible that R73-470 ohm resistor is open or high. Check the RCA's and REMJ1-remote gain control for broken or bent pins shorted to adjacent pins.
Yes rail is present and my 1khz signal run all the threw my preamp board. I'm looking at the R73, but can't seem to locate it. There are a few spots where the imprints have rubbed off the board. my voltages at j11:
1.) .611
2.) .612
3.) .598
4.) .601
5.) .600
6.) -14.02
7.) 15.49
8.) .601
9.) .598
10.) .601
11.) .612
12.) .601
1.) .611
2.) .612
3.) .598
4.) .601
5.) .600
6.) -14.02
7.) 15.49
8.) .601
9.) .598
10.) .601
11.) .612
12.) .601
Attachments
Yes rail iand regulated voltage present and my 1khz signal ran all the threw my preamp board. I'm looking at the R73, but can't seem to locate it. There are a few spots where the imprints have rubbed off the board. my voltages at j11:
1.) .611
2.) .612
3.) .598
4.) .601
5.) .600
6.) -14.02
7.) 15.49
8.) .601
9.) .598
10.) .601
11.) .612
12.) .601
1.) .611
2.) .612
3.) .598
4.) .601
5.) .600
6.) -14.02
7.) 15.49
8.) .601
9.) .598
10.) .601
11.) .612
12.) .601
I've spent some time looking at the pictures you posted and cannot find R73, so next best thing is to check with an ohmmeter from Power Ground to Speaker Ground.You will see a capacitor charging and should settle around 470 ohms. Post your measurement,I'm not sure if this version has a resistor R73//capacitor C36 between grounds or may be a jumper.
I posted an edited version of your pic. I believe this is the muting circuit. You may be able to read and confirm the parts I noted with the locators printed on silkscreen. In any event check the DC voltage across the Z3-20v zener. Check the across R46-47Kohm. Both should be around 20volts DC. R45-3 Kohm should have -28volt rail on one side and 20 volts DC on the other. Be sure to make this measurement and the next from Speaker Ground. The last measurement will be at the junction of R34-10Kohm and R42-100Kohm. This DC voltage is coming from the soft start circuit and should be around +12-13volts DC. If you hold the probes black probe on speaker ground and red probe on the same junction as you power up the amp you should see the voltage slowly ramp up from around 5 volts to ~13volts DC.
I posted an edited version of your pic. I believe this is the muting circuit. You may be able to read and confirm the parts I noted with the locators printed on silkscreen. In any event check the DC voltage across the Z3-20v zener. Check the across R46-47Kohm. Both should be around 20volts DC. R45-3 Kohm should have -28volt rail on one side and 20 volts DC on the other. Be sure to make this measurement and the next from Speaker Ground. The last measurement will be at the junction of R34-10Kohm and R42-100Kohm. This DC voltage is coming from the soft start circuit and should be around +12-13volts DC. If you hold the probes black probe on speaker ground and red probe on the same junction as you power up the amp you should see the voltage slowly ramp up from around 5 volts to ~13volts DC.
Attachments
That is the 470 Ohm resistor i found as well , in betwwen the connectors, it is within tolerence. Still my problem is related to this curciut, i beleive. I can see the 1khrz signal on the outputs, yet if i connect a speaker nothing.
It's possible that R73//C36 are not connected to PWR GND or Spkr GND due to open/burnt trace or cold solder. Check between PWR and Spkr GND's with an ohmmeter, you should see capacitor charging and meter settling around 470 ohms. If this looks okay, check the mute circuit as I lined out earlier.
Something is open. It was charging then not? The diodes test ok and I touched up alot of old soder connections all in that area. It reads 5.90Mohms
Is this from GND to GND? You said that the R73 is in value, 470 ohm,correct? Check from either side of R73 to either GND. If one side is open, you can then focus your attention on that side of the board. You may find an open/burnt trace on bottom side of board.
Ok so two grounds read 464.3 and two positive terminals read 464.3 red on same side of the 470r..the other terminals read in mohms range. They are connected but the signal at the speaker terminals is muted. There is only 500mv 1khz of audio at the output transistors. Grounding at the speaker terminal the sinewave is not clear.
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So that resistor I was questioning about in the muting curcuit is open. I believe it to be a 0ohm resistor but it's lost it coating so I can't tell.
That fixative has likely become conductive and corrosive. Any component that is in contact with it is suspect. All of it needs to be removed where it contacts any part of any component.
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