Sony BVM Fault

[retrogizmo]

I've picked up an old Sony BVM 2010P which wont power up. The PSU appears to be working (to a degree) as when you press the power button the lamp behind the logo lights up, and the indicator lamps come on, but it then powers itself off again within a split second. The overload light comes on, however as this is related to CRT overdrive, I don't think its relevant.

My first step was to re-seat all the sub-boards, but this hasn't affected anything. Next step if taking the PSU out and checking that.

If anyone has seen a problem like this before it would be good to hear from you.

[retrogizmo]

I've done some more digging and it seems like the PSU GB board which handles shut-down in the case of over-voltage is shutting the PSU down after very short period. All voltages except the 18v line seem to be sensible, but the +/-18v is more like +/-22v.

As far as I can see the 18v line comes straight from a tap on T1 through a rectifier and filter, so I'm not sure how that's coming out high given the other two taps for 15v and 5v seem to be correct.

[mvsfan]

Ive had Tvs give all kinds of start up issues. its usually related to bad or cheap capacitors in the power supply.

Ill give you an example. My DLP tv started burning out lamps really quick, id replace it within a couple weeks itd be burnt again.

After i recapped the power supply the problem went away. the current bulb has been in there a few years now.

I also had an Lg flatscreen Tv that would shut off after about 5 minutes. recapping the power supply also fixed it.

[retrogizmo]

Cheers, that's going to be my next step. None of the electrolytics actually look bad, no bulging or anything, but given they're the best part of 30 years old, they're not going to be at their best...

Curious its only one rail which seems out of whack. Could be the smoothing caps on that particular rail are dry and causing some nasty ripple I guess...

[retrogizmo]

Ok, recapped and still getting the same issue.

I wish I knew what the two LED's meant on the GB overvoltage protection board. When the monitor shuts off the "LOW-B" LED is lit on this board. If I start the monitor up with no load while probing one of the test points it clicks for a few seconds then comes up with the "HIGH-B" LED instead. If I knew what they were, that could help...

Next step, I guess figuring out exactly what the GB board does might be an idea.

[buttersoft]

I wish I knew what the two LED's meant on the GB overvoltage protection board. When the monitor shuts off the "LOW-B" LED is lit on this board. If I start the monitor up with no load while probing one of the test points it clicks for a few seconds then comes up with the "HIGH-B" LED instead. If I knew what they were, that could help...

Interested t hear how you get on. I have one of these sets as well, and will no doubt be looking for guidance when it eventually dies. From what I can see, the overload light normally comes on during power up. Then it goes away. Mine is off during operation, save on the brightest pure white screens. But if I turn down the contrast the overload light doesn't come on at all, save during power-up. It might all be explained by the fact the units are 30yrs old, as you've noted.

[retrogizmo]

I wish I knew what the two LED's meant on the GB overvoltage protection board. When the monitor shuts off the "LOW-B" LED is lit on this board. If I start the monitor up with no load while probing one of the test points it clicks for a few seconds then comes up with the "HIGH-B" LED instead. If I knew what they were, that could help...

Interested t hear how you get on. I have one of these sets as well, and will no doubt be looking for guidance when it eventually dies. From what I can see, the overload light normally comes on during power up. Then it goes away. Mine is off during operation, save on the brightest pure white screens. But if I turn down the contrast the overload light doesn't come on at all, save during power-up. It might all be explained by the fact the units are 30yrs old, as you've noted.

Yes, that sounds right. The overload is actually to do with overdriving the CRT, so a warning rather than an actual problem. If you fancy powering the monitor up with the PSU out (it comes out like a drawer, bottom rear of the monitor) and top cover off, I'd be interested to know if you get any LED's light up on the little sub board that comes out of the main PSU board.

There are two LED's, HIGH-B and LOW-B. Looking at service manuals for other BVM's (there's no info on this in the 2010P service manual) they light to show an error in either of the voltage blocks. With mine on startup I get HIGH-B light up, then the monitor shuts down.

I've been reverse engineering the GB board to try and figure out what it does. I'm not very good at this, so it may take a while, but it seems to be a latch which is triggered by the voltage being out of range which then kills the voltage regulation and shuts down the PSU. One of the service manuals also mentions over-current protection as well. I'll post up a schematic of the GB board once I've traced it out fully, I expect others will make more sense of it than me.

[buttersoft]

Sorry, yes the overload is a beam-current measurement, or at least I thought it was. There was another thread on here last year about a guy with a 2010 on which the overload light would come on, and shortly thereafter the set would shut down - if he didn't turn the brightness down. He then had to reseat all his option cards to get the set to fire back up again, including the standard, required five. He may not have had to do that if there's a better way to reset that latch you speak of.

As I understand it, with a simpler set, the B+ powers the flyback, which in turn is what controls the beam current through the grids and the primary HV. Or, at least, it will be affected by the beam current. Thus it might be linked to the overload light. Assuming the B of high-b and low-b for the 2010P is B+, are you able to measure it? It's going to be 150VDC or something? There should be key voltages listed in the SM, surely. I have the SM, but haven't had to pore over it.

I'm not going to get time to open my 2010 in the near future, but if you remind me in a few months I'd be happy to.

[retrogizmo]

Ah interesting. I thought B+ was a low voltage rail just from looking at the circuit. This is what the high-b overvoltage schematic looks like from reverse engineering it from the PCB:



I need to get a load of readings from everywhere and try and figure out what its doing. I can do digital electronics pretty well, but it'll take me a while to get to the bottom of this.

[retrogizmo]

Found the proper schematic -- B+ appears to be KICK. Which I believe is used to start the PSU operation.

[retrogizmo]

Ok, interesting, while the +150v line is actually good, the -150v is not going much below -8v. May have found the problem...

[buttersoft]

I would have guessed at the 150v+ line being the B+? Not that that's where the problem seems to be

[retrogizmo]

Ok, this is more like it, tracing back through the -150v section of the PSU I've found a diode which has failed and shorted open. This is screwing up the smoothing on the -150v rail. Time to get a replacement and see if anything else has blown.

[retrogizmo]

New diode in, and it now powers up. The screen displayed without any input attached isn't filling me with hope yet though, a bit of a white mess -- about what I'd expect with no hsync and an odd white framed picture. Not sure what these monitors should do with no input, but I would have thought a black screen.

Time to get a signal into it and follow it through again!

[buttersoft]

Nice job!

[LDigital]

After powering up, with no signal you should get a black screen. I urge you to take a look at the control board I mentioned before, it's a common fault area that will almost certainly need a recap and cleanup. Mine was a complete mess of leaking caps when I got mine but it now works like a dream. They are all surface mount

Edit: it may have been in another thread that I said that.
The control board is under the metal of the pull out panel. It has all the other pull out board controls plugged in to it

[retrogizmo]

After powering up, with no signal you should get a black screen. I urge you to take a look at the control board I mentioned before, it's a common fault area that will almost certainly need a recap and cleanup. Mine was a complete mess of leaking caps when I got mine but it now works like a dream. They are all surface mount

Edit: it may have been in another thread that I said that.
The control board is under the metal of the pull out panel. It has all the other pull out board controls plugged in to it

Thanks for that, I will take a look. I've tracked the issue down (as mentioned in that other thread) to the video amp shutting down very quickly after start-up. It could be something related to the control panel board... it's very difficult to tell.