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Old 16th Jul 2019, 11:22 pm   #1
dj_fivos_sak
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Default Sanyo VTC 5350 dead after replacing PSU caps

Hi all! I have a Sanyo 5350 Betamax (PAL/SECAM 5300) that doesn't power up after replacing all power supply capacitors. It was powering up OK before doing so. I double-checked the polarity of the caps and the fuse isn't blown. All it happens is I can hear a high-pitched whine comming from the PSU board. I also tried a replacement TL494CN IC but that didn't solve the problem. The board also has these components:
C1983
A1104
CTU-2R (dual diode)
B536
I get 0 volts on each leg of C1983. So that's probably the problem? The machine doesn't have an STK module like the VTC 5000/5150/5550. See attached photos. Any help would be greatly appreciated.
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Old 17th Jul 2019, 10:40 am   #2
Welsh Anorak
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Default Re: Sanyo VTC 5350 dead after replacing PSU caps

I suppose it's stating the obvious, but check, check and check again everything you've done. I suspect there's a broken track somewhere, and your lack of voltage is the first place to start. Don't forget a short across this capacitor will cause the tripping as well as an open circuit, so a solder splash is certainly possible - or even a faulty capacitor - it has been known!
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Old 18th Jul 2019, 11:18 am   #3
dj_fivos_sak
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Default Re: Sanyo VTC 5350 dead after replacing PSU caps

So... the coil whining stopped and then I found a shorted zener diode. I guess I'm in bad luck... :/
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Old 19th Jul 2019, 9:17 pm   #4
McMurdo
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Default Re: Sanyo VTC 5350 dead after replacing PSU caps

These things happen. I fixed a blown SMPSU this week which worked all day on load cycling the power occasionally. I added a bead of silicone to the main capacitor and let it set overnight, and the next morning..its dead, and what's more I can't see anything wrong!
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Old 20th Jul 2019, 7:37 pm   #5
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Default Re: Sanyo VTC 5350 dead after replacing PSU caps

Bang. I now found two shorted zener diodes. I really don't know how this happened... The 12V rail was shorted to ground until I removed the second zener.
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Old 22nd Jul 2019, 5:39 am   #6
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Default Re: Sanyo VTC 5350 dead after replacing PSU caps

So, I just hard-wired the 12V rail to an external power supply, and the unit turned on (except for the display of course). I even tried a tape and it played fine on my B/W set. However, I won't plug both power supplies in as I want to avoid further damage to the machine. But at least this tells me that the 12V rail isn't shorted elsewhere in the machine...

Fivos
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Old 24th Jul 2019, 2:40 am   #7
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Default Re: Sanyo VTC 5350 dead after replacing PSU caps

The 12V rail had probably gone high because of the bad caps.
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Old 24th Jul 2019, 3:30 am   #8
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Default Re: Sanyo VTC 5350 dead after replacing PSU caps

For security, Fivos check all caps on the SMPS.
Ideally need to replace it all with a 105 C type; is a better solution.
From the primary side to secondary side of SMPS.
The fault of missing 12V rail is on secondary side.
Check components on the rail of 12V.
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Old 24th Jul 2019, 10:02 am   #9
Maarten
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Default Re: Sanyo VTC 5350 dead after replacing PSU caps

105 degrees is only a secundary characteristic. They need to be low impedance (low ESR), which mostly come in 105 degrees. Not all 105 degrees caps are low ESR.
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Old 24th Jul 2019, 9:04 pm   #10
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Default Re: Sanyo VTC 5350 dead after replacing PSU caps

Thanks for the replies guys! This is what happened when I switched the external power supply to the 15V rail (Always 15V as listed in the manual). The machine fully powers up with both the machine and the external PSU plugged in. So what I'm thinking is the always 15V rail is required for the rest of the (switched) rails to work. I'm running the 15V rail with 12V since that's all I have. The VFD display is a liiitle bit dimmer than it was with full power from the internal PSU. But the ON/Standby buttons work as expected so the second half of the power supply is at least working... Insterestingly enough, all factory caps are 85C. The 12V rail was actually low with the old caps and that's the reason why I proceeded to replace them, which resulted in a somewhat dead PSU. I have also attached the schematics of the PSU.

Fivos
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