Panasonic SA-MAX770 (not turning on)

[Amraks]

Hey all its been awhile since I have needed to post here.

Panasonic - SA-MAX770: Symptoms not turning on

Power Supply
C1403 has 330v

IC1402 Looks perfectly fine no blown out holes.

C1601 has 3.3v


CN1851 Has its 3.3v but no 15v all I am getting is on the 14v rail is 0.400v

Not sure where I should be looking next for this any help would be appreciated

[rddube]

Re: Panasonic SA-MAX770 (not turning on)

If you keep power off, what resistance to ground do you get on the 15V rail pin of CN1851?

Disconnect CN8001 and check the resistance reading again on CN1851 15V rail.

I had a similar issue on a different model (Cambridge Audio) and it turned out to be a small mylar cap that had shorted on the 15v rail deep down inside. I used a thermal camera to see what was heating up and bang, there it was.

[Amraks]

Re: Panasonic SA-MAX770 (not turning on)

resistance to ground looks good nothing shorted out there.

measuring voltage at Vsen on pin 2 of ic1501
Is 1.5v could R1501 to R1504 be bad.
I believe this is meant to be 3.5v

[R_J]

Re: Panasonic SA-MAX770 (not turning on)

Do you have VC1 on pin1 of ic1501? What is your voltage on CN1851, pin4 (PCONT)?

[Amraks]

Re: Panasonic SA-MAX770 (not turning on)

Do you have VC1 on pin1 of ic1501? What is your voltage on CN1851, pin4 (PCONT)?

Pin 1 has no voltage.

correct me if I am wrong but isn't PCONT just going to ground?

Also I have been using wrong ground to measure Vsen using the right ground i get 3.3v

[R_J]

Re: Panasonic SA-MAX770 (not turning on)

PCONT is the Power CONTrol pin, it is used to turn ON the power supply. If there is no VCC on ic1501, the sense pin means nothing, the ic is not operating at this point.

PCONT goes to (P1) on page 71, then to (P1) on page 72 and then to PCONT on the base of QR1601 which turns on Q1405 optocoupler, which then turns on Q1402 which supplies the vcc to ic1501

[Amraks]

Re: Panasonic SA-MAX770 (not turning on)

Ok there is no power on VCC of IC1501.
Confirmed using ZA1101 heatsink as the ground.

And there is no voltage on Pcont.

[Amraks]

Re: Panasonic SA-MAX770 (not turning on)

with everything disconnected I have measured the mainboards pcont.
it is measuring short to ground.
I have checked IC8007 pin5(en) to ground and its reading short to ground.

[Amraks]

Re: Panasonic SA-MAX770 (not turning on)

found the shorts.
So have a short on IC8005
injected some voltage to find him.
Then injected some voltage to the SW pin 10 of that IC8005 as there was a short on that line which lead me to a short IC8003 removed all these off the board.
then found the sw pin short on IC8003 so I injected voltage and found that ic4803 was getting hot.
removed IC4803 and short was gone.

Now IC4803 was not on the schematics we have here I have found that version and I will upload here with this post.

shorted IC's by order.
1. IC8005 - TI45 54140
2. IC8003 - QVB? OVB? OYB? QYB? (this is a +3.3V DC/DC CONVERTER not sure where I can get this any help would be good. I am thinking it could be the tlv62065)
3 IC4803 - Yamaha YDA174

[Amraks]

Re: Panasonic SA-MAX770 (not turning on)

PCONT is the Power CONTrol pin, it is used to turn ON the power supply. If there is no VCC on ic1501, the sense pin means nothing, the ic is not operating at this point.

PCONT goes to (P1) on page 71, then to (P1) on page 72 and then to PCONT on the base of QR1601 which turns on Q1405 optocoupler, which then turns on Q1402 which supplies the vcc to ic1501

Thank you RJ for getting me this far.

[R_J]

Re: Panasonic SA-MAX770 (not turning on)

So is it only IC4803 that is bad and the other ic's are ok with IC4803 removed? IC8003 seems to be a TLV62065DSGR, use a magnifier to make sure of the number but it is likely QVB

IC8005 is likely a TPS54140

[Amraks]

Re: Panasonic SA-MAX770 (not turning on)

I took them all off in order so no way of knowing if they were bad, is it possible for them Frist lines to be short to ground and be still be fine with ic4803 removed.

I think I'll replace all just to be sure than wait another two weeks for chips to get here.

Not sure what could of caused this fault.
I need to read up on the Yamaha chip
You could see some discolouration around the edge of the chip looks like it got very hot at one stage.

Excuse me if this post is not formatted properly I am typing this on a phone today.

[Amraks]

Re: Panasonic SA-MAX770 (not turning on)

probably a bit late of a reply but this was solved by replacing all listed chips.