1984 Sony shutting off randomly

[Jimmyhaflinger]

Hi,

I have found a 1984 Sony KV-2252 in a skip, it works but it sometimes shuts off at random intervals, it may work for hours then shut off twice in 15 minutes, when it shuts off, the display keeps displaying the preset number and the keyboard remains functional, it just loses audio, video and EHT/deflection,

When it shuts off, i have to switch it off from the mains switch, wait a few seconds, then switch it on again and it may work well, or may die immediately and take several attempts to stay on.

The CRT seems to be at 100% and produces one of the finest pictures i've ever seen, bright, crisp and with superb colours, actually i've never seen such a good picture on a Trinitron before, this makes this set worth saving

I don't think it's a dry joint issue as i've banged the chassis hard while the set was working and it didn't shut off, so what should i check before venturing in a total recap?

[Michael Maurice]

I dont think a recap will help you. Caps that are failing normally behave badly/erratically when they are cold and improve as they warm up. One thing that did give problems to Sony's of that era was the 33µF/160V HT smoothing caps, though I'd expect your set not to start at all if this was the case.

The chopper transformers often go dry jointed. I would suggest you remove it to see if there is any sign on burning where the pins go into the transformer. Dont just resolder, remove all old solder then apply fresh solder.

Otherwise I'm afraid its down to some good old fashioned fault finding.

When the fault occurs, what happens to the 135V rail? If its OK at the power supply then it should be present on the line output transformer and transistor.

I hope this is of help to you.

Michael

[geofy]

Could be the line O/P transistor. The line drive stage should also be checked.

g

[Michael Maurice]

Jimmy did say that the set could run for hours before the fault occurs.

Unless the line o/p transistor was intermittently going O/C which I've never had, it would seem unlikely.

Hopefully Jimmy will get back to us with his findings and measurements whilst the set is displaying a fault

[ben]

in my experience, these problems really are usually a dry joint, even if you think you've checked 'em , get the magnifier out and go over the power and line stages, check also for fine board cracks maybe as a result of being chucked in the skip!

[geofy]

Originally Posted by Michael Maurice

Unless the line o/p transistor was intermittently going O/C which I've never had, it would seem unlikely.

Yes transistors usually fail completely, could be a dry joint around the Line O/P transformer, or the driver stage. Capacitors in the power supply or line output could cause this if pulses are not getting through due to a dried up electrolytic, some of the smaller values can suffer this. But as Ben says, could be just a bad joint or break somewhere.

Geof

[HamishBoxer]

Dry joints i would say,best thing get the head magnifier on or you wont spot them.Power supply area and any regulators are favourite.

David

[Peter.N.]

Dry joints on the field timebase chip were common on Sony's of that era, they would cause the symptoms you describe. Check all the others while you are there.

[gec2110]

what sort of 2252 is it
thier were 2 versions the rx and the pe3
they both used to suffer from dry joints
esp the east / west moduel
solder the chopper transformer and the line drive transformer
take them out and clean the pins and then resolder
have a look at the condition of the mica washer to the line output transistor
change it and the earth connections which run around the pcb

[Jimmyhaflinger]

It's a KV-2252-ET (the Italian version)

I've replaced a 22mf 250v capacitor near the LOPTx as its top was slighly bulging, the Sony is working on the bench now, i'll let you know if it shuts off again.

[gec2110]

The big differnce is in the layout of the pcb
one has a seperate power supply which is mounted on the degausing sheild on the side of the crt
and the other has the powersupply incorprated in the main chassis
the seperate power supply one which i think is the PE3 (dont hold me to this)
much better to work on

[Jimmyhaflinger]

The model i have has the power supply on the main chassis, while the tuner-IF board is mounted on the CRT shield

I also worked on the later chassis with the separate power supply in the past and i still have the service manual for this version (the RX chassis) but not for the PE3 chassis i have now

[Jimmyhaflinger]

The Sony no longer shuts off now, but a new fault appeared, the picture has faint darker bars rolling down the screen fast when the set is cold, they disappear after about 15 minutes.

Maybe that's due to dried up capacitors in the PSU secondary?

Also the stereo decoder doesn't seem to work, the audio stays mono even when the set is tuned on a stereo channel, but since this set uses the Italian/German Zweiton stereo system instead of UK's Nicam, i'm not sure if this is the right place to discuss this

[Michael Maurice]

Check the capacitor that is on the 200V rail to the RGB output stages.

Nicam wasn't available until 1987/88 and the only way of obtaining stereo on these Sony TV's was to feed it with a stereo source, ie a videotape.

I cant comment on the Zweiton system.

[dsergeant]

Italy uses the Zweiton (two tone) system with the main sound subcarrier (L+R) at 5.5MHz and a second sound subcarrier at 5.742MHz (R). I am not familiar with those decoders, but have occasionally encountered imported sets with it, which of course are totally incompatible with Nicam. I imagine fault finding would be quite straightforward.

Dave

[Dr-Watts]

Originally Posted by ben

in my experience, these problems really are usually a dry joint, even if you think you've checked 'em...

Agreed, especially in the power supply and around the LOPT, secret dry joint on the earth pin springs to mind...