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Old 6th Jun 2021, 7:09 pm   #1
Lloyd 1985
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Default 1980's Sony PVM-1270Q monitor

...And my attempt at reviving it!

I said I wasn't going to be bringing in any new stuff, lack of room and all that! But when forum member crestavega offered this one I couldn't resist, especially as it was destined for the bin if no one took it! I was told via PM that the monitor had worked well, until one day it just wouldn't come on.

It arrived in good order, but an old repair to a cracked power PCB opened up again, so that was dealt with using superglue and bits of stiff copper wire harvested from some scrap 2.5mm T&E cable to bridge the tracks. With that done I gave it some power, this monitor runs from 110V, so I used the variac set to 110V. The power light came on, as did the light telling you which input is selected, the speaker made a faint hiss as if the amp was working too, but no EHT, in fact no activity from any of the deflection circuits! A check with the meter shows all voltages present from the power supply, the 110VDC rail is high at 122V, and won't go down any further with adjustment of the '+B adjust' pot, but I guess that's high because the line stages aren't running, maybe it'll come down a bit once that's drawing current.

I've downloaded a manual for it, well, for the PVM-1370Q, which seems to be the European version that runs on 220-240V, I did try the manual for the PVM-1271Q which looks almost identical, but is a totally different beast inside. Looking at that there is one IC responsible for both horizontal and vertical deflection, IC501, which is a Sanyo LA7802. From looking at it with the meter, and the scope, it's getting power, but there's nothing coming out of it at all, every pin is showing nothing but flat DC voltages on the scope, so either it's sat in some sort of standby or protection mode, or it's dead.

So with that in mind I've rigged up some bench power supplies, and a function generator for some crazy experiments! I thought maybe if I feed in the low voltages (12V, 18V, there is a -30V too, but I've left this out for now) and also stick up to 60V on the +B line (should be 110V) and feed in a 15.625kHz signal to the base of the horizontal driver transistor I should be able to fire up the line stage, if it's all good... The line output transistor and the driver transistor are good, but I've no idea if the LOPT is any good, if all goes well, and my experiment works, I should get some EHT, right?

Well, first impressions are that all is well! I fed in the signal, via a cap just to make sure nothing nasty goes back up to my function generator, switched on the 12 and 18V supplies, and slowly wound up the 60V supply, once it got to around 55V I heard a slight crackle around the CRT, and a faint whistle from the LOPT! Turning the signal on and off made the crackle of static come and go, as you would hear from a working set when switching it on and off. I also hung a meter on the CRT heater pins and the heater voltage came up too, albeit low because I'm only running on a current limited 60V supply, instead of the full 110V.

So what's next? I think I need to dig around that IC and make sure everything's OK round it before condemning it to the bin, unless anyone knows different and says just go straight in and change it? The IC isn't cheap, so I need to be sure it's not something else before I change it, don't want to blow up another straight away!

Regards,
Lloyd

Service manual available here
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Old 12th Jun 2021, 5:46 pm   #2
Lloyd 1985
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Default Re: 1980's Sony PVM-1270Q monitor

Thought I should update this

After the first lot of experiments I decided to try and up the +B line a bit, I added some old SLA batteries and got up to 70V, still not quite 110V! After winding up the screen control I was able to get a line on the screen, confirming there was no frame scan, I checked the oscillator with the scope and sure enough there was nowt happening. I gave the oscillator output a poke with the meter set to continuity test and was able to make the line jump up and down on screen, so the frame output stage is good, as well as the line output stage.

Over on the VRAT forum it was suggested that if the frame stage was not working maybe the set would go into some sort of protection mode to stop a line getting burnt into the screen, so I went on a hunt to see if it was something to do with the frame stage, but as far as I can tell, the frame output stage only gets power once the line stage is running, as the voltage to the frame output IC comes from the LOPT, as does one of the VCCís for the LA7802 IC, which has both line and frame oscillatorís in it.

IC 505 is responsible for ĎHV Hold downí, which connects to the LA7802ís ĎX-Ray protectí pins, so I had a prod around there and found that the only voltage present was the 20V on pin 8, some of the others quickly flicked up by a volt or two when power cycling the set.

I did wonder if it was because the +B was high at over 120V, it should be 110V, so I decided to try loading the 110V line with a 40W lightbulb, that did bring the +B down, and I was then able to set the voltage to bang on 110V, but the monitor remains dead! Some of the voltages did come up on the pins of IC-505, but not by much.

Iím still thinking the LA7802 is toast, so Iíve ordered another, I canít think of where else to go with this! The monitor had originally been used on a ship, so itís been exposed to salty sea air, and there are a few components with rusty legs, a few transistors and some of the tiny resistors, but so far all have measured perfectly ok.

Regards
Lloyd

I also gave it a clean, and took a new photo of it in better light! Donít suppose anyone has the control panel flap sitting in a box of junk?!
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Old 12th Jun 2021, 9:39 pm   #3
Maarten
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Default Re: 1980's Sony PVM-1270Q monitor

IC505 gets its signal from the line output transfomer and from the HSTAT unit. Both could be broken as well. You should doubly make sure it isn't getting activated through one of those signals.
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Old 13th Jun 2021, 11:37 am   #4
Lloyd 1985
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Default Re: 1980's Sony PVM-1270Q monitor

Hi Maarten,

I did a load of tests last night, checked the connection from the H-STAT to the IC, all is well there, also checked the path from the LOPT to the IC too, all seems ok there too, there are some extra components in this monitor that aren’t on that circuit diagram, in fact there’s a whole PCB that’s not on it! It also has connections to IC505 with wires tacked on to the bottom of the PCB, it’s definitely an official Sony mod looking at it.

There are no voltages coming from the H-STAT or LOPT to the IC, but I guess that’s because the line stage is not doing anything, it doesn’t even attempt to start up, so no voltages ever come up from that area. The only way I got it to fun was by injecting my own external 15.625kHz from the function generator, I’ll try it again later and see what voltages come up.

The thing that makes me think the LA7802 is duff is that when I first tried powering the monitor I checked the voltage going into pin 17, one of the VCC pins, and it was something daft like 70V+, I didn’t think much of it at the time, but since getting the service manual I see it’s supposed to be 12.4V, and it shows a zener diode built into it. Now it seems the voltage on pin 17 is only getting to around 8V, and it fluctuates. I’m sure it’s not the resistor feeding it, that measures ok.

Regards
Lloyd
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Old 15th Jun 2021, 9:09 pm   #5
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Default 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 wasnít 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 didnít 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 itíd 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 doesnít go over 12.4V. If it looks like itís going to, and nothing goodís 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 didnít 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 itís 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 Iíll have to get brave and connect up the mains power supply and see what it does, hopefully not go pop!

Regards

Lloyd
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Old 22nd Jun 2021, 8:03 pm   #6
Retrotechie
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Default Re: 1980's Sony PVM-1270Q monitor

I have a similar set, a PVM-1371QM, which is from 1985. It had sadly been dropped, and i bought it as such. On further investigation, the CRT base had several cracks, which i repaired. Still no picture, but EHT and heaters up, so promising. I then discovered large cracks on the input PCB at the side of the monitor, so more resoldering and jumper wire, but still no joy. Its currently on my 'rainy day' pile.

These sets dont take well to being banged around, and sometimes the finest cracks can prove elusive.

Sony would have sold thousands of these sets to tv production companies, educational establishments etc

Mine is missing the front control panel flap-i think most probably are, so not holding out much hope to find one.
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Old 23rd Jun 2021, 12:31 pm   #7
Lloyd 1985
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Default Re: 1980's Sony PVM-1270Q monitor

Hi,
Sounds like you got a real job on your hands with that one! I had a PCM-1444QM once that had been dropped, the tube had broken its mountings but was still intact, until it got shipped to me! Sadly it got necked, and bounced around on top of all the boards, smashing them to bits in the process, that one ended up in the bin, as I was never going to find a tube for it. It sounds like yours is nearly there! Can you get anything on screen by adjusting the screen control?

This little monitor is working well, Iíve had it up on full mains with its own PSU, well 110V full mains, as thatís what it was designed for! Several more capacitors protested at being woken up, and Iíve yet to place an order to get new ones. There are some purity errors on screen, but other than that it all looks pretty good! Iíve been trying to find a suitable RGB source for it, I tried a nice Sony HD camcorder, but that was component output only, and this monitor doesnít like it! It shows a very green unlocked picture! Next to try was a Sony PS2 console, but I havenít got the right cable for that, and that has power supply issues of its own that need sorting out, so next to try is a SCART adapter, so I can use a DVD or Freeview box with it.

The photos are of the monitor displaying on full mains, and the repair to the print side of the PSU, and also the re-jigging of components, I moved a resistor to the print side as it was crammed in with 2 caps and it was heating them up a lot!

Regards
Lloyd
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Old 27th Jun 2021, 7:24 pm   #8
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Default Re: 1980's Sony PVM-1270Q monitor

Hi Lloyd, thatís a great picture, excellent work.
Good shout re adjusting screen volts-I will check that.

I have a couple of the PVM-1444s tucked away, which I believe are the successor to the PVM-1371QM, and also multi standard. Itís worth noting that the tube on the PVM-1444 is exchangeable with that used in the BVM-1415/1416, (and possibly others) although there are equally few of these around these days.

Regards,
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