Sony PVM CRT repair

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sbadger
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Sony PVM CRT repair

Post by sbadger » Thu Oct 25, 2018 1:28 pm

Hi there,

My lovely pictured Sony PVM has gone weird. !
Not sure if there are any CRT experts out there but felt it was worth at least asking on here.

When I turn on the picture comes on, (a bit over bright) and over about 60 seconds the picture slowly fades to nothing (including OSD bits).

I've checked for cold joints on the neck board (the neck/heater is glowing even when picture has gone dark), and recapped the neck board) but not dice.

here is a vid
https://youtu.be/Y2E4fYxlzF4

Any thoughts?

thanks
stewart
So many projects, so little time...

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sbadger
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Re: Sony PVM CRT repair

Post by sbadger » Tue Nov 06, 2018 2:08 pm

I've done a bit more work on this. I've recapped the power board but problem remains.
The board is outputting -23v on the -15 rail so am looking to replace the regulators next.

stew
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1024MAK
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Re: Sony PVM CRT repair

Post by 1024MAK » Tue Nov 06, 2018 3:14 pm

A very overbright picture may mean that the current flowing through the electron guns is too high. Most CRT sets have a protection system, such that over a certain level, it will shut down all or part of the set. Some protection designs latch and some don’t (so the set may then cycle on and off).

In your case, as you have found higher than expected supply voltages, it sounds like a power regulation feedback system is malfunctioning (as in there is no feedback, or it is not representative of the monitored voltage rail).

Again, various power rails often are monitored via protection systems, and if tripped, can cause the set to shut down, or partly shut down.

Some CRT sets have a SMPSU (Switch Mode Power supply unit) which produces most power rails, then some further power rails derived from auxiliary windings on the LOPT (line output transformer). All CRT sets will have a HT (high tension) rail of between about 100V and 150V).

Whatever power systems are used, the main supply rails will be a winding, a half wave single diode and one or more capacitors. These should be regulated via a feedback loop system. Some auxiliary supplies may use series pass voltage regulator chips (78xx series, or other makes/types, often with many more pins/legs)

Have you got / found a schematic for this set?

Mark

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Re: Sony PVM CRT repair

Post by sbadger » Wed Nov 07, 2018 7:44 am

1024MAK wrote:
Tue Nov 06, 2018 3:14 pm
A very overbright picture may mean that the current flowing through the electron guns is too high. Most CRT sets have a protection system, such that over a certain level, it will shut down all or part of the set. Some protection designs latch and some don’t (so the set may then cycle on and off).

In your case, as you have found higher than expected supply voltages, it sounds like a power regulation feedback system is malfunctioning (as in there is no feedback, or it is not representative of the monitored voltage rail).

Again, various power rails often are monitored via protection systems, and if tripped, can cause the set to shut down, or partly shut down.

Some CRT sets have a SMPSU (Switch Mode Power supply unit) which produces most power rails, then some further power rails derived from auxiliary windings on the LOPT (line output transformer). All CRT sets will have a HT (high tension) rail of between about 100V and 150V).

Whatever power systems are used, the main supply rails will be a winding, a half wave single diode and one or more capacitors. These should be regulated via a feedback loop system. Some auxiliary supplies may use series pass voltage regulator chips (78xx series, or other makes/types, often with many more pins/legs)

Have you got / found a schematic for this set?

Mark
Thanks Mark I do indeed,
https://ia600600.us.archive.org/1/items ... Manual.pdf

Mine is the PVM-20M4E model.

i'm going to replace..

IC603 : NJM78M05FA
IC604 : TA7805S
IC605 : TA7812S

Is there another regulator I should change?

Thanks
Stewart
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Kazzie
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Re: Sony PVM CRT repair

Post by Kazzie » Wed Nov 07, 2018 9:38 am

With regard to the -23V output on the -15V rail, is that on the power supply board (board G)? And is that with the other boards connected or disconnected?

If it's that far off when disconnected, I'd be worried about the T603 transformer, as the only things between it and the -15V output is a rectifier made of D615, C628 and C629. If the rectifier's fine, replacing that transformer will be tricky, as original replacements (Sony part 1-431-245-11) seem hard to come by.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM (mid- restoration)
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Re: Sony PVM CRT repair

Post by sbadger » Wed Nov 07, 2018 12:38 pm

Kazzie wrote:
Wed Nov 07, 2018 9:38 am
With regard to the -23V output on the -15V rail, is that on the power supply board (board G)? And is that with the other boards connected or disconnected?

If it's that far off when disconnected, I'd be worried about the T603 transformer, as the only things between it and the -15V output is a rectifier made of D615, C628 and C629. If the rectifier's fine, replacing that transformer will be tricky, as original replacements (Sony part 1-431-245-11) seem hard to come by.
Hi Kazzie, yes that is -23V while G board disconnected to A.

I've already renewed C629, (but not ceramic C628)

I'll check the diode later.

How do transformer fail? i thought they were fairly static as it were. ?
Last edited by sbadger on Wed Nov 07, 2018 12:52 pm, edited 1 time in total.
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Re: Sony PVM CRT repair

Post by Kazzie » Wed Nov 07, 2018 12:55 pm

sbadger wrote:
Wed Nov 07, 2018 12:38 pm
Hi Kazzie, yes that is -23V while G board disconnected to A.

I've already renewed C629, (but not ceramic C628)

I'll check the diode later.

Do how transformer fail? i thought they were fairly static as it were. ?
(Simple) Transformers are two lengths of wire wound repeatedly around an iron core. The wire is generally very thin, and has a fine layer of plastic or resin around it as an insulator.

If the insulation deteriorates over time, the wire may short out against itself or the core. A power surge could also cause heat-damage to the insulation. A short circuit on the primary winding could change the ratio of turns between the primary and secondary windings, and thus change the output voltage.

(Transformer windings can also fail open, where the wire in one of the windings fails, and you get no output voltage. I've had that happen to a CRT's loopback transformer recently.)

Rewinding a transformer by hand is not fun. I tried it with a simple (two winding) transformer, and had to give up and buy an "almost-fits" replacement instead. Rewinding that T603 transformer, with its multiple windings would be a whole lot more difficult.

Here's hoping the fault is elsewhere.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM (mid- restoration)
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1024MAK
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Re: Sony PVM CRT repair

Post by 1024MAK » Wed Nov 07, 2018 1:44 pm

Apart from LOPT, most transformers are very reliable unless abused.

If the output of a secondary is higher than expected, it is best to see what is happening on the primary side.

Mark

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Re: Sony PVM CRT repair

Post by 1024MAK » Wed Nov 07, 2018 5:09 pm

PVM-20M4E - chassis SCC-G62E-A
Mains AC input 100 to 240V AC

So, referring to PDF pages 42/43, 64/65 (manual page numbers 45/46, 76/77), AC mains comes in via CN601, goes via some fuses and interference suppression circuitry, then goes to board J (power switch) via CN602. An AC mains supply returns back to board G via the same connector. Then the AC is rectified by bridge rectifier B601 (MAIN RECT) to form a DC supply. On the schematic this is shown as 110V DC, but in the U.K, a full wave rectified mains voltage becomes 339V DC.

The main switch mode regulator control chip IC601 (STR-M6524) then drives transformer T603. The feedback is via IC602 (STR-S3115) and opto-isolator PH601 (PC111YS).

If the feedback system is not working properly, IC601 will not be able to adjust it’s output drive to the transformer (T603) to the correct level.

So please test/check the voltages at the following points:-
PH601 (PC111YS) pins 1, 2, 4, 5 noting that there are different 0V/ground lines for the primary and secondary sides of T603. And noting that the primary side is connected to 240V AC mains via the bridge rectifier.

Mark
Last edited by 1024MAK on Wed Nov 07, 2018 5:09 pm, edited 1 time in total.

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Re: Sony PVM CRT repair

Post by sbadger » Wed Nov 07, 2018 6:35 pm

That's a great steer thank you Mark & Kazzie,

When I checked the output from the G board (when connected to A and running)

the +15v is stable at 14.98v
the +115v is stable at 114.7v
and as we know the -15v is -20v and climbs to -18

It'll probably be the weekend before I can check PH601 and the D615, after work today I need a beer and HV and beer are a no no [-X :D

I'm compentent enough with CRTs to be safe and have done many recaps of arcade cabs and monitors but have never had to do any real repair so am enjoying this. It's such a cracking screen I would be great to get going again.

thanks
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Re: Sony PVM CRT repair

Post by sbadger » Sat Nov 10, 2018 1:20 pm

I just did a reading of the PH601

1 : 0.005v
2: 102.4v
4: -108.8v
5: -86v


assuming i got the right ground... :roll:

stew
So many projects, so little time...

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