Re: Help with Sony SLV-N750 VCR

"G B" <geeberry@xxxxxxxxxxxxxxx> wrote in message news:y4Jfl.48235$8a4.39372@xxxxxxxxxxxxxxx

"Arfa Daily" <arfa.daily@xxxxxxxxxxxx> wrote in message news:wZ8fl.7570$1s3.6110@xxxxxxxxxxxxxxxx
"b" <reverend_rogers@xxxxxxxxx> wrote in message news:d28c65b1-42f1-4dbd-8447-b1907cf101dc@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On 23 ene, 04:51, "G B" <geebe...@xxxxxxxxxxxxxxx> wrote:
Hi,

I have a Sony SLVN750. It failed such that it had no time display and
would no longer power up when pressing the power switch. I tore it apart
and "shot-gun" replaced the nine capacitors in the general area of the power
supply with capacitors of the same value. It now will power up and even
play a tape BUT when it is powered down (in standby) the display blinks on
and off. It seems the power supply is cycling on and off. Any idea what
would cause this? Any help is appreciated...


"G B" <geeberry@xxxxxxxxxxxxxxx> wrote in message news:8T4fl.29$np4.6@xxxxxxxxxxxxxxx
The display isn't flashing per say...

The display goes blank after the supply apepars to shut itself down. It returns after say 500 msecs.. then stays on for about a second.. then goes blank and starts again. Also every time the display blinks, the carriage motor appears to go through its position check...
I did replace the all the "big" electrolytic caps.. the largest were a couple of 1000uF... I suspect that section of the circuit is working properly.. I think there must be a standby power section of the circuit which is toast... any ideas?


Have you replaced any electros in the front end or were they all secondary side ? This sort of odd behaviour in switchers can be symptomatic of small caps - often only from 1 to 47uF in value - situated around the oscillator / control IC having gone high ESR. You will often find them located close to some other component or heatsink, which runs hot. Do you have an ESR meter ? Just as an aside, it makes a thread and the replies much easier to follow if you bottom-post rather than top. :-)

Arfa



I replaced 9 caps all in the area of the switcher, or at least where I think the switcher is. I replaced the large regulation cap (82uF @ 200V) and I replaced a small (4.7uF@50V) on what I would consider the primary side. (prior to the large transformer). I replaced all the electorlytics: 10uF, 100uF, 330uF, 470uF, and 1000uF values on what I think is the secondary. Do you know if the switcher provides the boot-strap voltage in standby mode? Or do they have another regulator somewhere off the line regulation circuitr? I have also what appears to be a hot-spot on the circuit board around QIP107, RIP110, QIP108, ZDIP05, and DIP109. It doesn't feel warm to the touch after it has been running for a while.. so the hot-spot is a bit of a mystery. I don't have an ESR meter here. I guess I could probe the removed components at work... of course I don't know what the ESR of the original caps. I thought I could use a DMM to get an indication, but it must be marginal enough I can't tell which one is the bad actor.

As for the posting at the top vs bottom... thank Outlook for always starting at the top rather than the bottom of the post ;)



Likely scenario:
The hot spot on the board was caused by the over-voltage at that point, caused by the bad caps. You replaced the caps - now the voltage there is normal. This presumes the zener diode, which is what got hot, did not just short.

Mark Z.

.

Relevant Pages

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