Hey everyone, lurker coming here to post for the first time :)
Was browsing eBay and came across a listing for a 'for parts' PVM 20M4E at a decent price - the seller described it as 'turning on but not producing an image'. This is the 20" 800 TV scan line European model and was very desirable to me, so I took a gamble and decided to buy it and maybe get it repaired. I'm in the UK and it's far, far harder to come across Sony PVMs like this unless you get one of the fresh-out-the-NHS medical versions (with the MD code in the name and white facia). Sony PVM 20M4E
What was interesting about it was that it came from Aardman Studios
originally. A sticker on the back and an email from the studio confirms this set was used around the time that they produced animated classics like Wallace & Gromit and the Wrong Trousers/Grand Day Out so it had a bit of history to it as well which added to the value for me. Cheese Gromit?
Anyway I picked it up and without turning it on, opening it up, or doing anything with it, I took it straight down to a fella in London - guy is an ex-broadcast technician - to have a good look at her. His workshop is like something out of a dream for this sub lol - CRTs of all shapes and kinds stacked on top of each other, spare parts and cables strewn everywhere, was kind of awesome tbh.
As expected she turned on, produced a bright green raster, but the menu was off the screen and couldn't be accessed in any way shape of form. Diagnosis? Someone had gone into the service menu, adjusted the Vertical Blanking settings bringing the menu off-screen, and then written those values to the ROM irreversibly. My guy said that this was a complete write-off and completely unrepairable unless I somehow got a new ROM chip or managed to load the correct standard values back into it to fix the over-blanking.
Disheartened, I took it back home and left it for a few days. Decided I would try and sell it again on eBay for parts or repairs as my predecessor had, but I couldn't help turning it on one last time and having a quick stab through the menus (armed with a very stark warning from my friend who said that many of these TVs die at the hands of people who don't know what they're changing in the menus :P).
To my surprise, it now produced a blue raster and VERY faintly in the bottom left hand corner of the screen I could read 'NTSC'. Don't remember this happening at the workshop or in the seller's description so I delved a bit further. Looks like some retrace lines as well as the blue?
I managed to get the user menu up too! It was barely visible and not surprised we hadn't noticed it before, but just visible enough now for me to see where I was navigating when viewed from the top down. This is good I think, because that means the V Blanking issue we thought it was couldn't possibly be the problem with it now - if I can see the menu then at least I have got that to work with, as opposed to before. A spark of hope? Maybe it isn't a lost cause anymore.
I remember my repairman had pointed out to me the part in the monitor's manual where all of the default values for the service menu settings were laid out. He said unless those values are written back into the ROM she's a goner. So I got myself a PDF copy of the manual online and decided I would try and reset all those service menu settings back to their 'standard' values again and see if that made a difference. Excerpt from the service manual - from left to right - first column is the feature numbeidentifier, second column is the category, third column the option being adjusted, fourth column the maximum setting, and final fifth column the standard value it should be set to (or around that, give or take what the original service man changed for this particular set).
I went through every one of the 120 service settings available and changed them to what the manual said. Some of the values varied very little and were close to the standard value, but some had clearly been changed to something way above expected, so I reset these ones to the value stated in the manual. The picture improved quite noticeably - looking much sharper and the menu was now clearly visible and no longer faint. The user menu after resetting the service options to the default settings specified in the manual. Looks much better. Note the blue and pink colours - no green anywhere to be seen.
however one option that I simply could not change back to it's standard value - our old culprit V Blanking <60>! This adjusts the vertical blanking when in 60hz NTSC mode. It was set to maximum (255) - and if I lowered it to the manual-recommended 161, the menu would completely disappear off of the bottom edge of the screen, producing a completely blue screen with wobbling sides. Eek! I adjusted it back to the maximum again and made sure I wrote this value in so that the monitor wouldn't be left in limbo as had previously been feared.
From left to right you can see that 'Other' is the category, '255' is the max value, '91' is the numerical ID of the setting, and 'V BLANKING <60> is the name of the setting itself. V BLANKING <60> is set to 255 (maximum - as I found it) - any lowering of this value beyond about 200 would take the menu off the screen completely.
When the monitor is put into 50hz PAL, that blue wobbly screen already exists, so I suspect that someone has screwed with the V BLANKING <50> option and written it to the ROM. Because of this, if I try and access the menu in PAL I of course can't see what I'm doing, so adjusting it to try and bring the menu back would be futile. This is what he says happens to a lot of PVMs - people try and get the picture perfect, or they try to get rid of RGB lines, and they end up making huge adjustments and then writing them to the ROM permanently.
ANYWAY. This is where I am right now. I have made sure all the user settings, service settings, and knobs on the front are all standardised or zeroed. Only exception being the V BLANKING <60> which is set to max or else the menu will
fall off the screen forever. She's in a lot better shape than she was before - now I have an accessible menu, I know that the settings are roughly right for most things, and that the monitor isn't a complete loss yet. The next thing is figuring out - what is the problem then?
Let me just say now that I know next to F-all about these machines, but here's my hunch: a capacitor or two have gone bad in the deflection or neck board, which is what led the original owner to adjust the V BLANKING so high in the first place. Since I'm in the UK he was probably on PAL, which is why the 50hz blanking is completely gone, whereas I can still access and configure in NTSC. I would take a look inside myself but I'm terrified of getting a shock and would rather a professional do that job.
I'm hoping that I can take it back to my guy now that the menu is accessible again, and maybe he can have a look inside, take some voltages, and check for any domed or leaking capacitors on the board. He's yet to get back to me on this - he may after all just tell me that it's not worth it. I've heard that broken neckboards (which can be bridged back again) are often the culprit in faulty Sony PVMs of this era too. As a bonus, here is what happens when I turn on the 'Blue Only' button in NTSC: Screen goes bright green and then image is lost, red tally light at the top turns on. Too much voltage?
Finally, I can hear sound coming from the box perfectly when my N64 is plugged in with either composite or S-video. I have tested the N64 on a much smaller JVC monitor and both inputs work fine so it's definitely a fault with the telly (duh).
So... now that I've told you guys everything I know and the story so far, do any of you in your wisdom have any recommendations or ideas about which parts have gone or if there's anything I can try myself before I take it back to the shop again? I'm determined to get this thing fixed now after all the trouble I've gone through and would love to hear your thoughts :)
Thanks for reading