Re: SMPS help needed - Philips VCR

Franc Zabkar <fzabkar@xxxxxxxxxxxxxxxxx> writes:

On Wed, 6 Aug 2008 14:34:17 -0700 (PDT), ajuniper@xxxxxxxxxx put
finger to keyboard and composed:

There is a short (~0.5s) squeal from the PSU when mains is applied.

I have annotated the diagram with the measured voltages (in red) and
indicated the components I have pulled and checked; the diagram can be
found at http://www.ajuniper.f2s.com/psu.jpg (2MB image).

Thanks,
Andy

Check for shorts on the secondary outputs. I'd suspect a shorted 18V
protection zener (DO15) on the AL+15V rail.

Quite possible.

Some of the voltages don't make any sense around Q003. For example,
1.2 V across B-E of a normal NPN transistor, and +1.5 and -1.5 on the
IC001. But this might be due to there being some AC as the PSU
repeatedly tries to start up, not just DC voltages, and this is
confusing your meter.

While you're at it, it would be worthwhile to check the electrolytic
caps for ESR and uF. If the zener is shorted, the cause may be bad
caps.

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