...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