cap exploded in a vintage VCR

[jack black]

I procrastinated with transferring my old family recordings on DVD. finally i plugged in the circa 1993 multisystem VCR and heard a pop and saw a flame. the VCR was last used several years ago, could this be a factor?
A small electrolyte cap blew in the power supply. i have no idea what value and voltage. i searched the web for schematics and nothing showed up (toshiba V-880ms). what would you put in?

[budm]

Re: cap exploded in a vintage VCR

At you need to show us the location of the caps so we can see what the function of that cap is. Any pictures of the old caps and the board?
Service manual:
http://elektrotanya.com/toshiba_v-88.../download.html

[jack black]

Re: cap exploded in a vintage VCR

At you need to show us the location of the caps so we can see what the function of that cap is. Any pictures of the old caps and the board?
Service manual:
http://elektrotanya.com/toshiba_v-88.../download.html

you are good, i searched too and even was on the same website but downloaded another, corrupted rar. this zip was good and i found the cap C831, 47uF, 25V, and i actually have a spare one!

than you, thank you, thank you.

[RJARRRPCGP]

Re: cap exploded in a vintage VCR

Sounds like the primary got shorted to the chassis.

[jack black]

Re: cap exploded in a vintage VCR

Sounds like the primary got shorted to the chassis.

what do you mean? i replaced the exploded cap and plugged the (disconnected from vcr) power supply in. the 1.6A fuse started glowing and another big cap (1000 uf/25V) got hot and swollen.

another bad cap or f....ed up power supply?

edit: power supply was not screwed to the metal cage when i tried. maybe that was a mistake.

[tom66]

Re: cap exploded in a vintage VCR

Fuse glowed, or blew? Most fuses are about to blow when they start glowing.

I suspect the power board has a problem with output regulation, maybe the output voltages are too high.

If it's an old VCR, it's probably a first-generation self-oscillating SMPS, possibly based on a ringing-choke converter. They are known to blow a load of parts when they go bad, so repair can be very difficult.

[jack black]

Re: cap exploded in a vintage VCR

yeah, i pulled the power when i saw the glowing. i put a new 1000 uf cap and the same problem, the power supply is toast. weird, it worked fine last time i used it.

question, if i buy used toshiba vcr on ebay, will it have similar power supply? the reason i'm trying to save this one, some of my tapes are recorded on PAL camera and this is the only one that can play them.

[RJARRRPCGP]

Re: cap exploded in a vintage VCR

Sounds more like an irregular waveform. I would get an oscilloscope!

[R_J]

Re: cap exploded in a vintage VCR

Those caps are getting too much voltage, I suspect the str-d1706 not operating properly, I would change the caps C812, C813 & C809
Then check the dc voltage accross c820, It should be around +15 volts
Its possible the regulator ic Q801 is also bad.

[stj]

Re: cap exploded in a vintage VCR

i used to repair vcr's

if the str hybrid is suspect, then you need to replace all the caps - because one probably killed it to begin with,
and you need to meter all the resistors, and check all the soldering because anything stuck to a heatsink probably has cracked joints.

when we did beltkit&pinchroller jobs, we always replaced the caps simply because once these things blow, it's a much bigger job than a pre-emptive re-cap.

[jack black]

Re: cap exploded in a vintage VCR

Those caps are getting too much voltage, I suspect the str-d1706 not operating properly, I would change the caps C812, C813 & C809
Then check the dc voltage accross c820, It should be around +15 volts
Its possible the regulator ic Q801 is also bad.

i measured the voltage. it goes from 28 to 32V in the few seconds before i disconnect power. no wonder the caps blow.

looks like i'll be replacing the strd1706 and the related caps.

i also noticed the board near d811, d813, and f803 is discolored, probably heat. could bad diodes cause the problem too or be faulty in addition?

i have to admit i don't understand how that power supply works at all.

[stj]

Re: cap exploded in a vintage VCR

check *everything* before you power it up again.

[jack black]

Re: cap exploded in a vintage VCR

one more question. there is a piece of wire short (from the factory) in the place of C813. should i leave this in place or replace with a real cap?

[Th3_uN1Qu3]

Re: cap exploded in a vintage VCR

Leave it be. A capacitor is an open circuit to DC, short only to AC. If there is a wire bridge in that place it means it was never supposed to have a capacitor there in the first place.

[CapLeaker]

Re: cap exploded in a vintage VCR

Don't replace factory stuff... just replace those parts that you know are bad.

[R_J]

Re: cap exploded in a vintage VCR

It looks like c812 & c813 are in series each is marked as 120uf @25v. I bet the factory installed a 47-100uf@50v in c812 location and jumperd c813.
Whats the value of the cap. in c812 location?

[jack black]

Re: cap exploded in a vintage VCR

Whats the value of the cap. in c812 location?

100/25. you think it should be 50V?

[jack black]

Re: cap exploded in a vintage VCR

i think i fixed it. replaced C812 with another good 100uF/25V and got 15.5V in the output. the old C812 worked, but with decreased capacity. every other component i checked was fine.

[R_J]

Re: cap exploded in a vintage VCR

If the original was 25volt you will be ok. If you have a 50 volt one you could use it instead but its not necessary.

[jack black]

Re: cap exploded in a vintage VCR

It looks like c812 & c813 are in series each is marked as 120uf @25v. I bet the factory installed a 47-100uf@50v in c812 location and jumperd c813.

i thought about why there were 2 caps in series. then i thought it's a safety issue in case one of them shorts. somehow the factory ignored it. the irony is the mode of failure was the opposite, loss of capacity and that produced quite dramatic effects, cap fireworks and busted components on the control board that i'm trying to fix. goggling for this shows a common problem in toshiba VCRs of that age. looks like the cap plague existed for a long time before the recent pandemic.