Pioneer VSX-859RDS center driver blown

[Rupsenkind]

Hi all, I've a Pioneer VSX-859RDS on my desk where the owner tried to improve the sound quality by using the idle current adjuster without a voltmeter.... indeed as the drivers are Mosfets he managed to blown them so the parts needed to be changed as the unit went into protection mode all the time:
- First I ran into the issue that the service manual of the VSX-859 does not contain the power amp diagrams but I found that the Pioneer VSX-35TX does have them included.
- Also found in another forum that parts in the driver stage could be damaged and indeed I found 2 burned resistors > replaced all
- Once I turned the unit back on with all parts replaced, the main fuse blew instead of going in protection mode, replaced fuse to be sure the old one was not weak but new fuse blew as well. Investigation showed that the replacement of Q2542(2SC4137) wasn't an isolated TO-126 housing so installed a mica isolation part > still fuse blew
- Now looking at the power amp PCB I do see a transistor/IC which is not listed/reflected in the SM (Q2552), it's a part with 6 legs, no description on it (see attached photo) and Google wasn't helpfull either. As the part is in the power amp section I just want to replace it to be 100% sure.
Long story but does anyone have any experience with the VSX-859 power amp and has an accurate service manual where all parts are reflected?
Many thanks for your replies and support....

[R_J]

Re: Pioneer VSX-859RDS center driver blown

Post a picture of the installed Q2542, I suspect even with the mica insulator it is still shorted by the screw.
Post a picture of the complete board where Q2552 is located
Clean the flux from the top of the component so we can see the markings.

[Rupsenkind]

Re: Pioneer VSX-859RDS center driver blown

Hi R_J, here you go:
- Picture 1, complete PCB
- Picture 2, snapshot of Q2542 mounted (copper screw mounts Q2542)
- Picture 3, snapshot of Q2542 without the metal mount strip (Q2542 sits in the middle)
- Picture 4, cleaned Q2552, now a text is visible looks 420 or 428 with XI or IX below)
- Picture 5, a Q2542 replacement

I doubt that the copper screw is still causing shortage as if you look at picture 5 you can see the hole in the 2SC4137 is isolated and with the mica plate between the back and the cooling frame it should be isolated.
In the meantime I also found an Pioneer internal memo (also attached) where the recommend to swap the caps C2013,033, 053, 113 and 2113 if a mosfet has been damaged and the device has been activated multiple times in protection mode untill smoke was detected (and this is what happened with this device), so I've ordered these caps and will replace these as well.
Looking forward to any other tips, tnx!

[lotas]

Re: Pioneer VSX-859RDS center driver blown

X1

[Rupsenkind]

Re: Pioneer VSX-859RDS center driver blown

Hi Iotas,

many thanks for this but how sure are you that this is the right component as it's not listed at all in the SM? Do you have a SM which is reflecting the correct PCB + components? Tnx!

[R_J]

Re: Pioneer VSX-859RDS center driver blown

Is there a mica insulator behind all 3 transistors?
This is the correct component that is in your picture, IMX1 You can also check each internal transistor to see if they are ok or not
There was a factory modification where the original board was replaced

[R_J]

Re: Pioneer VSX-859RDS center driver blown

After a closer look it looks like there is one large insulator behind all 3 transistors, check that there is no debris between the transistor and the insulator
I also see I attached the same pdf, If this has the modidied board I suspect the rest of the modification was already done as well

After a closer look I don't think the 2sc4137 is even connected on this board, it is likely just used as a seperator for the heat sink mount. The IMX1 is used in its place, and they only use one of the transistors and the other transistor leg is just used to couple the heat to the IMX1. so if the one transistor IS bad, you should be able to use the other transistor (if it is good) by turning the ic 180 degrees

Which two resistors were blown? that might help in the diagnosis

[lotas]

Re: Pioneer VSX-859RDS center driver blown

hi iotas,

many thanks for this but how sure are you that this is the right component as it's not listed at all in the sm? Do you have a sm which is reflecting the correct pcb + components? Tnx!

q2552

[Rupsenkind]

Re: Pioneer VSX-859RDS center driver blown

Tnx R_J and Iotas,

looking at the info you provided I agree as well that the modification already was implemented in this unit as Q2552 is now present on, what I assume, the new PCB. I've checked if debris is between transistor and insulator but it's clean.
For the blown resistors: it was R2552 and R2057 on the V-AMP board. I've tested Q2047/2048 but they were ok, just to be sure I've replaced C2053.
Need to put all together and test but I'll be travelling the coming 10 days, so will provide an update once I'm back. Tnx again so far for your support!