Sony PVM-20M4E Blowing HOT and other ICs

[agardiner]

I would be changing all of the capacitors mentioned regardless. Given its age, any of them could be causing problems.

[Retrorepair]

Absolutely. Some have already been changed but I've a shopping list for the rest.

[tiff_lee]

Hi all,
I just came across this thread when searching for some info on my PVM-20M4U (the US model) and there is some excellent information here. I certainly don't mean to thread hi-jack Retrorepair so apologies in advance but seeing that this topic was discussing the power supply model I thought it would be an appropriate place to ask especially since the thread is current.

The service manual covers both the 20M4U and 20M4E but states the former is 120V only while the latter is 100-240V. The schematics however don't differentiate between power supplies showing only one design/list of components.

I'm going to remove the cover and double check what components are actually fitted on mine but the manual seems to suggest it's the same board despite the manual stating 120V in the info section at the start.
Essentially there is clearly some very experienced individuals here who I figured may be able to offer some insight, thanks.

[Maarten]

The commercial spec sheet at https://www.broadcaststore.com/pdf/m...5997/pvm20.pdf mentions 100-240V for the PVM-20M4U.

Strangely, Sony usually used the U suffix for destination UK, and I seem to remember the R for the USA. However the service manual explicitly mentions the U suffx as the US version.

[tiff_lee]

Yeah so I had a look inside and everything is as per the service manual, all components are rated accordingly to handle 240V but the PSU actually triggers overvoltage protection and shuts down if I use it, I think there is actually some underlying issues already as the -15V is up at -18.5V when using 120V so i'll need to address that first.

@Retrorepair, might be worth checking this video out

https://www.youtube.com/watch?v=R2Up...nnel=RetroTech

He talks about a red green blue line fault and V blanking but around the 6 min 30 sec mark he refers to some caps (C-572 & C-584) on the A board that fail due to heat from a nearby IC. When those caps fail they cause the nearby IC to fail and an IC on the PSU to fail, sounds familiar? or maybe just a coincidence.
In the video description it states the "20M4" model is affected.

[Retrorepair]

Thanks, those caps were already replaced though. The half hour it was on before going bang again there were no symptoms like that.

Does anyone know where to find the STR-M6524 and STR-S3115 by the way? I've ordered some from Aliexpress but honestly I don't trust them at all.

[Retrorepair]

Ok, progress update.

Finally got the chinese parts and installed them, have also changed all caps mentioned and the two slight out of spec resistors with beefier ones for good measure but have a new problem.

I thought I'd just test the psu before powering up the whole monitor and disconnected the 3 connectors to the main board in the corner. Then testing on the larger pin header, 5v sits at 5.08v until I hear a tiny tick in the middle of the psu then gradually falls. -15v is reading -22.5v, 15v is reading 4ish volts and 115v is like 0.05v. Anyw ideas where to start looking now? Feel like that last bang took out more than I'd realised ��

[agardiner]

Are you able to post the power supply section of the schematic?

[Maarten]

Hard to say wthout a schematic, but you might want to check the rectifier and electrolytics on the 115V line for shorts.

[Retrorepair]

I think it's too big to post here as an image but the service manual is here: https://archive.org/details/SonyPVM2...4ServiceManual

The PSU (G) board scematic is on pages 63 and 64.

I'm thinking two possibilities, either a tiny trace on the STR-M6524 pads came away or one of the regulators got taken out last time it blew up. I'd much prefer the first option!

[Retrorepair]

Originally Posted by Maarten

Hard to say wthout a schematic, but you might want to check the rectifier and electrolytics on the 115V line for shorts.

Does the 115v line power up without load? I'd expect to see something there as I'm thinking there's only a few diodes and a transformer in that path.

[Retrorepair]

I should add, one solder point was iffy so I touched it up. No change other than 15v (pos) now shows 15.6v until the tick sound then falls along with 5v. 115v never shows more than .22v and -15v is a fairly constant -22.5v

I'm gutted tbh, I thought I'd be able to trouble shoot the original issue at least. Now I dont know where the heck to go.

I should also point out I changed PH601 and on the A board the HOT. Both from Cricklewood to make sure my transistor wasn't a fake (I hope). Of course the HOT doesn't come into it yet since I'm only testing the PSU.

Starting to give up hope with this now

[Maarten]

I had a look at the schematic. Your measurements mean the power supply is basically working but shuts down because of some fault condition, maybe through feedback provided by IC602 which itself could also be faulty, or some problem upstream or downstream from it.

[Retrorepair]

Originally Posted by Maarten

I had a look at the schematic. Your measurements mean the power supply is basically working but shuts down because of some fault condition, maybe through feedback provided by IC602 which itself could also be faulty, or some problem upstream or downstream from it.

That's only the IC itself (chinese.. suspect), the PC111 whoch came from cricklewood and I don't really suspect but who knows, and the transformer. I don't know where else to source a STR-S3115 so maybe this thing's done for.

[Maarten]

I'm not sure. The IC seems quite simple, but it's hard to find any datasheets for Sanken products.

Also, upstream there's a diode and an electrolytic that should be checked. Just measuring whether there's 115V at the input of the IC can be useful.

[agardiner]

I don't seem able to open the link.

I agree that it appears to be shutting down due to a fault condition. Are all the voltages derived from STR chip?

I used to repair these at work, but won't be able to pull the manual until I am next in on Thursday.

[Maarten]

As a side note: you can sometimes weed out forged STRs (and STKs) by rubbing them with a cloth soaked in alcohol while applying some force. No black should be visible on the cloth and the printing should not easily fade. Usually, forgers take a cheaper or more common variant in the same casing and resurface and reprint or relaser them. If there isn't a cheaper variant of this particular IC, chances increase somewhat that it is actually a factory original.

[Retrorepair]

Originally Posted by Maarten

I'm not sure. The IC seems quite simple, but it's hard to find any datasheets for Sanken products.

Also, upstream there's a diode and an electrolytic that should be checked. Just measuring whether there's 115V at the input of the IC can be useful.

Yeah think I just need to do some deeper investigation on this, I didn't really have time the other day. Hopefully tonight. The cap was replaced as a matter of course but the diode I'll check. Will check the input on that transformer too.

I didn't know about that trick for checking fake components, thanks I'll have a look. I think it's fairly unique in terms of the case but who knows?

[Retrorepair]

I tested the input and output on the STR-S3115 and the input starts at around 160v and then falls, the output does achive 115v (meter only picks up about 111v) then drops almost immediately.

Crap IC?

The schematic posted also isn't quite the same as the PSU in front of me. It shows several unconnected pins but they're all connected to something. There's a lot more between the output and the connector too.

I'm a bit lost now really.

[murphyv310]

I'd put my money on the chip.
It's important that you fit a chip with the same mask number as the OE component. Having been a Sony service technician I really cannot stress this enough, using a generic chip won't work they just fail sometimes in just a few minutes. The issue now is actually being able to source the correct chip.
Good luck.