UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - 1980's Sony PVM-1270Q monitor

Lloyd 1985 · 15th Jun 2021, 10:09 pm

ITS ALIIIIIVVEEEE!!!!

ok, so I did a load of tests around IC-505, with the function generator supplying the line stage, and decided from that, that everything seemed to be ok, and to go ahead and replace the LA7802, as it wasn’t doing anything useful, the VCC was low at only 8V, and fluctuating, and while running it like this the frame stage began doing something, just flicking up and down every so often. I had also tried supplying the VCC pin with 12V from the bench power supply and all that did was make the chip get warm.

It was during this round of tests that I noticed a cap, C701 on the CRT base PCB which is on the 200V rail, getting hot and bothered, it was very close to popping! I did stab the rubber bung after removing it and it turned into an electrolyte sprayer! As usual, I didn’t have a new one, but found one on an old dead SMPSU, so robbed that, tested it and fitted it.

The new LA7802 arrived today, so I decided I might as well bung it in and see what happens, 10 quid down the bog if it blows up, so not much at stake! I thought it’d be sensible to use the bench power supplies again, monitor the 12.4V VCC to the chip, and wind up the +B slowly, making sure the VCC doesn’t go over 12.4V. If it looks like it’s going to, and nothing good’s happening, stop and come up with a new plan... so up went the voltage, and somewhere around 9V (on the VCC) I heard a squeak from the LOPT! At this point my heart was racing, and I was beginning to shake! I continued upping the power supply and the VCC got to 12V and didn’t increase further, the crackle of static around the tube was noticed, the damn thing was running under its own steam! I plugged in the nearest video source I could find and I noticed the line whistle change frequency as it synced to it, the monitor was up against my workshop PC monitor, but I was able to get the mirror in so I could see the screen, I turned up the screen control on the tube base and the tube lit up with a picture!! And it’s in colour with decent frame scan too! Took a quick photo and then shut it all down. Then had to go sit down and have a drink to calm down!

So now I guess I’ll have to get brave and connect up the mains power supply and see what it does, hopefully not go pop!

Regards

Lloyd

15th Jun 2021, 10:09 pm	#5
Lloyd 1985 Nonode Join Date: Jun 2008 Location: Coningsby, Lincolnshire, UK. Posts: 2,820	Re: 1980's Sony PVM-1270Q monitor ITS ALIIIIIVVEEEE!!!! ok, so I did a load of tests around IC-505, with the function generator supplying the line stage, and decided from that, that everything seemed to be ok, and to go ahead and replace the LA7802, as it wasn’t doing anything useful, the VCC was low at only 8V, and fluctuating, and while running it like this the frame stage began doing something, just flicking up and down every so often. I had also tried supplying the VCC pin with 12V from the bench power supply and all that did was make the chip get warm. It was during this round of tests that I noticed a cap, C701 on the CRT base PCB which is on the 200V rail, getting hot and bothered, it was very close to popping! I did stab the rubber bung after removing it and it turned into an electrolyte sprayer! As usual, I didn’t have a new one, but found one on an old dead SMPSU, so robbed that, tested it and fitted it. The new LA7802 arrived today, so I decided I might as well bung it in and see what happens, 10 quid down the bog if it blows up, so not much at stake! I thought it’d be sensible to use the bench power supplies again, monitor the 12.4V VCC to the chip, and wind up the +B slowly, making sure the VCC doesn’t go over 12.4V. If it looks like it’s going to, and nothing good’s happening, stop and come up with a new plan... so up went the voltage, and somewhere around 9V (on the VCC) I heard a squeak from the LOPT! At this point my heart was racing, and I was beginning to shake! I continued upping the power supply and the VCC got to 12V and didn’t increase further, the crackle of static around the tube was noticed, the damn thing was running under its own steam! I plugged in the nearest video source I could find and I noticed the line whistle change frequency as it synced to it, the monitor was up against my workshop PC monitor, but I was able to get the mirror in so I could see the screen, I turned up the screen control on the tube base and the tube lit up with a picture!! And it’s in colour with decent frame scan too! Took a quick photo and then shut it all down. Then had to go sit down and have a drink to calm down! So now I guess I’ll have to get brave and connect up the mains power supply and see what it does, hopefully not go pop! Regards Lloyd Attached Thumbnails