Re: WG6100 heat problem

From: Pat Danis <patdanis_at_verizon.net>
Date: Thu Apr 12 2012 - 12:12:31 EDT

Well, I replaced Q606 just in case it was bad. I rechecked all
components in the circuit and all tested good. However, Q603 (and Q703)
were different transistors than anything I had come across in the past.

I missed them on my first go around on repairs and noticed this time
that they were TO-220 packages instead of the smaller MPS-U57/U07
variety. This particular transistor is marked 361-2 and on the bottom
of the chip, the Motorola symbol and 926 and what appears to be a
smaller font capital "L". These are mounted on the standard heat sink
but have a cutout to accommodate the larger transistor. They appear to
be some sort of factory replacement. Has anyone seen these before and
could you shed some light on their tolerances? I could not find a
datasheet on them. Here is a link to the photo of the transistor in
case you are curious:

https://picasaweb.google.com/pdkomodo77/WG6100Transistor?authuser=0&authkey=Gv1sRgCI--nZejz7ickAE&feat=directlink

I went ahead and replaced Q603 with a spare from a parts board in case
these are out of tolerance for the application. I left the Q703 as-is
to see what happens there.
Thanks for your help on troubleshooting this. I guess it was just a bad
transistor stuck open. It seems to be running at normal temperatures
now. I left it on all night just to be sure.

Pat

On 4/3/2012 2:45 PM, Patrick Danis wrote:
> Thanks Bill. I will report back with my findings after I
> troubleshoot. Wish I had stayed an EE major at school.
>
> Pat
>
> On 4/3/2012 12:23 PM, wboucher6@cogeco.ca wrote:
>> Unfortunately, there are several things that could cause Q606 to be
>> stuck turned on. I'll assume that Q606 is in fact
>> good and not leaking like crazy. Be aware that it might operate/test
>> okay when cool and go into thermal runaway once it
>> warms up enough. In that case, you'd also get a picture for a while
>> and I assume you are not.
>>
>> Faults that will cause your described condition:
>> - an open diode at D600, D601, or D602
>> - an open R611
>> - an open Q603
>> - a shorted Q601
>> - opens at any of R602, R604, Q602, R605
>>
>>
>>
>> Bill Boucher
>> http://www.biltronix.com
>>
>>
>>
>>> Been fixing 6100's for some time and this is the first time I have run
>>> into this issue. I have a monitor that was brought to me with the
>>> following problem. Q606 is getting extremely hot. So hot that the
>>> transistor socket is turning black like burnt toast and the frame is
>>> almost too hot to handle on the right hand side.
>>>
>>> Believe it or not, the transistor is still working. I have been
>>> through
>>> the deflection board several times and found nothing. I did find both
>>> power transistors bad so replaced those and the blown fuses and the
>>> socket on Q606 and it still will not come up. I only spent a few
>>> minutes on it as I had to leave town for business. I'm just curious
>>> what would cause the transistor to get so blasted hot.
>>>
>>> I will be getting back to it on Saturday to troubleshoot some more.
>>>
>>> Pat
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>
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Received on Thu Apr 12 12:10:12 2012

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