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phorvati
Joined: 11 Mar 2008 Posts: 2
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Posted: Tue Mar 11, 2008 6:22 am Post subject: SONY VPH-1031Q power Supply board(GA) |
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Projector worked fine for 8 years, but now its not powering up. I traced the problem to the GA board. I am looking to buy another one but they are hard to come by. So i was trying to isolate the problem on the board.
I seem to be blowing 1,2,3 or all 4 of the 2SC3163 transistors (Q601/Q602/Q603 and Q604) after about 10 minutes after power up. It happened twice already.
So I know that something is driving one or both amplifier circuits into self distruction.
Here is what I did so far.
All I have is a DMM with a diode tester so I cannot do any extensive testing.
I took out and tested all components in the two primary circuits: all of the diodes(RM2C), resistors, and capacitors for obvious shorts, or open circuits. None of the caps were shorted and diodes tested ok. The two transformers T601PRT.1 and T603PRT.2 (I assume tey are fall-back transformers) have small resistance in the primary and high in the secondary.
Besides the blown transistor pairs, I did find a problem with resistors R601,602 and R605,606. They were all supposed to be 460Kohm, but one was 1100Kohm. I was hoping that would be whats making the amplifier circuit unstable so I arderd a set of 4 along with and 4 new transistors. But unfortunately, B-E junction on Q604 blew up again after about 5-10 minutes. The 5A/125V fuse did not bow this time. Small piece of junction material fell off as well.
From reading about sony power supplys, its often the capacitors that are the cause of this.
There are many caps here. The large electrolytic polar capacitors, then there are the small ceramic disk ones and the blue ones with 4 pins as well.
Is there a standard set of parts that should be replaced in this case?
How simmilar is the CRT projector GA circuit to that of a CRT TV?
Any other items I should test?
Sincerely
Petar |
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