Repair Sony BVM 2010P

[Foquens]

Recently I've bought a Sony BVM 2010P for retro gaming, unfortunately it has an issue I have not been able to resolve yet.
It does not always show a picture. Sometimes when I turn it on it works perfectly, and sometimes it doesn't.
When it doesn't, the monitor seems to be powered though, also I can hear the degausing relay switching when pressing the degauss button.
Also I managed to measure a the +-12v on the GC board , and 150v rails on the PSU board, they seem to be fine. The -150v rail on the GC board however is another story. When the monitor works and shows a picture, the voltage is close to -150. When it doesn't it is close to -120V.

I have already replaced the C72 and C73 capacitors on the PSU board, but that didnt help at all.
Anyone has an idea what the issue might be?

See link for service manual: https://cdn.retrorgb.com/assets/monitormanual/Sony_BVM-2010p_Operation_And_Service_Manual.pdf

 

[Nigel Goodwin]

I suspect your getting confused by the voltage readings - the regulation is done from the +150V rail, so if the load is falling the -150V rail will most probably be low as well.

I should check round the LOPT stage, see if the line is running, as that's the major current draw. You need to be aware of fairly dangerous voltages round there, the pulses on the LOPT transistor when running are likely to be above 1000V.

 

[unclejed613]

how about the +150V rail? does it change too? the 150V rails are both driven by the same converter on the GB board.

 

[unclejed613]

Q103 is the output transistor. in addition to the FBT it drives a transformer that produces the filament voltage for the CRT. don't try to measure the collector voltage on Q103, as the >1kV spikes will fry most DMMs. if the filament of the CRT is lit, Q103 is working, if the tube isn't lit Q103 is not working.

 

[Foquens]

I will check the +150v rail tomorrow. How can I be sure that Q103 is the failing component in the system? Sometimes I have an image, and sometimes I have not. When I do, it works without any issues also for longer periods of time.

 

[Foquens]

Okay, I decided to check it today anyway. I turned the monitor on, there was no picture. I measured the +150V directly on the PSU and it is around +148V. I also measured the -150V, on the GC board, which was approximately -120V.

 

[Nigel Goodwin]

I will check the +150v rail tomorrow. How can I be sure that Q103 is the failing component in the system? Sometimes I have an image, and sometimes I have not. When I do, it works without any issues also for longer periods of time.

It's almost certainly NOT Q103 (assuming that's the LOPT?), it wouldn't be intermittent in that way.

Assuming it uses a line driver transformer?, it could be dry joint on the transformer - quite a common fault for intermittent line drive.

 

[Foquens]

I reflowed all the connections on the three boards in the back and the board with the flyback. Now it got even worse, even when there is an image, the image is very noisy and the EA board makes a lot of noise. Dont know what to do now

 

[Nigel Goodwin]

I reflowed all the connections on the three boards in the back and the board with the flyback. Now it got even worse, even when there is an image, the image is very noisy and the EA board makes a lot of noise. Dont know what to do now

Undo whatever you've done - by 'reflowed', what EXACTLY do you mean?.

 

[tvtech]

Scan coil plug. Solder those 4 pins even if they seem OK.

 

[Foquens]

I resoldered all the pins on the PA, EA and EB board and the flyback board. It shows a lot of noise on the monitor now and the EA board makes some noise now

 

[Nigel Goodwin]

I resoldered all the pins on the PA, EA and EB board and the flyback board. It shows a lot of noise on the monitor now and the EA board makes some noise now

You've probably shorted something out, you need to find and remove the short.

 

[Foquens]

I resoldered the EA board again, it seems to be much better now on the RGB input. Unfortunately the composite input still does not work. Only when I set the monitor to digital it shows a black and white image. No colour on the PAL setting

Appearantly you need to have slot B5 populated, otherwise the luminance-chrominance or chominance channel will not be activated on a composite signal. My mistake. The monitor works again, I fixed the issue I introduced earlier. But it only still sporadically shows an image. Not sure what to do next....

 

[tvtech]

Play with the G2 pot on the Loptx a bit....
Try turning it down a fraction...

Or try turning it up a fraction.

See what happens when you do. Wait a bit once you fiddle. Give it a few mins.

tv

 

[Foquens]

I will give it a try, just need to find the G2 controls, the lopt has no knobs......

 

[tvtech]

Check on the tube base board for a Screen pot than.

 

[unclejed613]

G2 is controlled by Q104, 105 on the PA board. their control signal comes from the BI board. there doesn't seem to be a G2 pot. the following transistors on the BI board are arranged as a diff amp with 3 noninverting inputs, and 1 inverting input Q11, 12. 13 14. Q15 looks like it's being used as a current mirror, which sends the output current to Q104, 105 on the PA board.

 

[tvtech]

Ok unclejed.

I always look for simple solutions to probs first
I guessed a bit lol

(I never downloaded the diagram given...I was on Mobile)

tv

 

[Foquens]

So no easy way to check if this would affect the issue I described

 

[Foquens]

Would I be able to measure the output of the HV protection circuits using TP5 and TP6 on the PA board?