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Mike
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PostPosted: Mon Feb 25, 2008 12:30 pm    Post subject: PTK195 convergence dies out after a few minutes Reply with quote

i got another one of these notorious PTK195s that convergence power supply poops out after a few minutes. What actually goes bad on these things? i checked all the caps for high ESR, and found none. the 10uf at 63 seems a little high, about 3ohms, but not bad...

any ideas??
Google

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Steve
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PostPosted: Mon Feb 25, 2008 12:30 pm    Post subject: Reply with quote

I may be wrong, but I'm thinking I replaced the STK730-130 on a couple of
195s this past year for shuting down after a few minutes and they have held
up so far.
JOhn
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PostPosted: Mon Feb 25, 2008 12:30 pm    Post subject: Reply with quote

Mike, Replace Cr19710, Cr19709 With p/n 164590. Also The stk 730-130 need to
be a reliable Sanyo type.
Check to be sure R19703 (750K 1/2) watt is not open or intermittent. Also
Q19700 (BC457) P/n 242675 Superseded by 250686, Or NTE 123A, Has been a
problem Could have B-E open.

Also You might check U19504 the OP amp> That can cause the convergence power
supply to shut down. Tritronic sells the kit 250686 Kit, That may have all
the parts need to repair that board.
Mike
Guest





PostPosted: Mon Feb 25, 2008 12:31 pm    Post subject: Reply with quote

250686 seems to be the entire board.
Mike
Guest





PostPosted: Mon Feb 25, 2008 12:31 pm    Post subject: Reply with quote

i put the parts on order for the STK, and the diodes. along with some caps.
might as well change them.

the buffer transistor BC457 off the opto tests fine, and the resistor off
its collector 750K is fine.

so we'll see what happens.
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Mike
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PostPosted: Mon Feb 25, 2008 12:31 pm    Post subject: Reply with quote

one thing i did notice when it does shut down, the STK heatsink is red hot.
Al
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PostPosted: Mon Feb 25, 2008 12:32 pm    Post subject: Reply with quote

Change the STK.
Jerome
Guest





PostPosted: Mon Feb 25, 2008 12:32 pm    Post subject: Reply with quote

I think you'll find that when the STK fails, it starts putting out a DC bias. Since it's
connected to a coil, that DC bias results in a LARGE current, which heats it up. If you look at the
schematic, you'll no doubt find that the STK is DC coupled to the stuff upstream - so an upstream
failure could also cause it to do so. HOWEVER, the STK is the hardest working chip on the board,
so it's probably the culprit.
Terry
Guest





PostPosted: Mon Feb 25, 2008 12:32 pm    Post subject: Reply with quote

Mike, there are a few I have had (out of dozens) that the CR19709 / 710 get
leaky. Also check R19714. Replace C19703 but leave the leads long and bend
it over and above R19703. The reason is that C19703 gets hot if too close to
the heat sink. I usually use STK730-010 instead of the STK730-130 because
you can never tell if they are Sanyo Or the Chinese version. Good luck.
John
Guest





PostPosted: Mon Feb 25, 2008 12:33 pm    Post subject: Reply with quote

Mike wrote:
250686 seems to be the entire board.


Mike, Not when you put Kit after the Number. 250686KIT
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