TV/VCR/Stereo Troubleshooting/VSX-D508 Pioneer
QUESTION: Still on this, sir. Have replaced IC401 & 402, (PAC007A) IC 403 (PAC008), Q1451 (IRF9540A) & Q1452 (IRF540A)as well as C715 & C716 (8200mfd @ 83 Vdc each).
The + and - 15 volts come upon CN112 pins 14 and 12, the B+ on C715 & 716 raises to about 56 volts then drops out as power off appears on display.
All connections are good, no pin shorts or opens on replaced parts, speaker lines have good 8 ohm speakers on them. Reading resistance from either spkr wire to ground gives a very high resistance, however reading resistance between either speaker ground and hot ( L+/L_ or R+/R_) shows completely open...no charging of cap or resistance. Is this because relay has speaker circuit open, or problem ?
ANSWER: It's been long time since thinking on this project.
I don't have documentation on file so either I dumped it or didn't find it. Question: Is there a relay at the audio output that comes on after power supply build up? Pioneer is famous for having that feature.
And, similarly, the relay cuts out when amp is turned off - or when it fails/protection mode.
The intended purpose of the relay is to avoid the "thump" in the speakers during turn on and turn off.
Looking into the relay driving voltage may lead you to the solution of the problem. If the relay is dropping out then we have to find out the cause.
So, look into that angle of it.
---------- FOLLOW-UP ----------
QUESTION: Yes, it does have the relay and the relay turns on, but when the "power off" message appears, the relay DOES NOT turn off until I power down the machine.
What gets switched when the relay closes and opens?
In some amps it switches the speaker output wires to ON after the B+ voltage has come up to full level. In other amps it switches on the B+ DC to the audio output stages when the power supply has reached full voltage.
Then if trouble is detected the relay switches off the DC lines so as to prevent internal damage to the circuits.
Thus you can troubleshoot by determining what may have caused the relay to go into melt-down mode....