[TechAssist] Re: Sony KV-27TS27
- From: "Damon" <damon101@xxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Thu, 20 Sep 2001 02:24:18 -0500
Hi,
I can suggest a couple starting points to look at:
Take a serious look at the Hot for bad connects, also the Hot's filtering
cap on the Hot's drive tranformer and the coupling cap on the Hot's B-E
circuit path. Sony has also stated to replace the green varistors if you
ever have blown the SMPS outputs, those are located right by the SMPS output
heatsink. Once you rebuild the SMPS, you can jumper the relay and using your
Variac, bring up the AC voltage to about 30Vac and take a look at the SMPS
output (Read it at the emitter to emitter connection of outputs). Verify
that the duty cycle of the oscillation is 50%, if it isn't then look
closely at the resistors and capacitors connected to the base to ground path
(these control the duty cycle) of the outputs. Sony allows a 3 - 5% maximum
variance of the duty cycle, but don't push these...if it checks ok, then
bring up your AC to 60 volts then 90 volts then normal AC voltage, keeping
an eye on the duty cycle and looking for transient spikes. There is a
capacitor attached in parallel with the primary side of the transformer that
controls frequency (50 - 53 khz is normal) and a transient capacitor
connected (I think) from the base to collector or base to B+ of the SMPS
outputs....These rarely fail, but in your case they may be bad. Jim Myers
and I had a real dog unit one time with this symptom, and he NAILED it. If
this doesn't help I'd talk to him.
Hope this helps
Damon
----- Original Message -----
From: "ACT Electronic Center" <act@xxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Wednesday, September 19, 2001 7:32 PM
Subject: [TechAssist] Sony KV-27TS27
> Hi can anybody suggest a tip on the unit?
>
> The unit is dead.
>
> I have replaced the transistors
> C4664 x2
> Fuse.
> unit is ok, but after 3 days, the unit break down again.
> I have replaced another transistors but still, the unit went dead, it is
destroying parts.
>
> Pls. Help.
>
> Dennis Co
> act@xxxxxxxxxxx
>
>
> Help make your TechAssist online repair tips
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