[PleaseEatEggs]

Hello all, first time here! I’ve recently decided to try to repair my fathers GDM-20E21 monitor, which has been sitting in a corner for about 12 years now after it suffered a power supply issue. The picture would take longer and longer to appear, until it stopped.

I have taken the thing apart to look at the G board, and nothing seemed awry, but I replaced the fuse and a suspicious varistor anyway. I reassembled it and hoped for the best, but alas. 

When the monitor is powered on, the power light is solid green for a few seconds, and then the power saving light flashes orange. After pressing the power button, there is a 1 second delay and then a high voltage click can be heard. After two seconds, another, and after two more, a third. After this, there is nothing. The screen never lights up at all. 

I’m quite stumped on this thing. Nothing seemed to be wrong inside the case as far as I could tell, but then again I cannot really find documentation or service manuals for this exact model. Any help would be greatly appreciated, as I’d love to get this thing working so I can plug our Octane into it.

Thanks again!

[weblacky]

This won't be of direct help, but there are Sony Trinitron-specific guides online (I've seen them), that said CRT technology is actually very complex in the voltages required (not including any adjustments, hopefully you'll require none).  I do have a couple GDM service manuals (not for your model) but they could be helpful.  Likely since it's sa low, slower, symptom...until nothing, you're likely dealing capacitors (fill-time/slower oscillations) changing/degrading.

example:
https://elektrotanya.com/sony_gdm-fw9011...nload.html

Possibly just sign up for this site (it's not easy, he asks quiz questions to prevent most people from applying) but this the best place to get manuals for similar GDM monitors:
https://elektrotanya.com/showresult?what...l&kat2=All

You can do five downloads a day for free, if you don't sign up.

My suggestion would be to unplug it and leave it alone for a while, then you'll need to remove the neckboard and the main PCB under the tube and go through and start writing down the cap physical dimensions, values, and markings, then you can come back and with some help, try to track down OK substitutes.  Dimensions of the cans and values/markings all matter!

If you find one of these service manuals has the same neck board description you'll likely get good test points for voltage tests to check various required voltages.  But I'd assume from your description, it's likely caps, replace them and it's highly likely it will come back to life (no guarantees on picture/image quality).  However there will be many, you'll need a desoldering gun to help prevent delamination, and for caps alone, be prepared for like $100 (or more) just in caps.  Also I'm told bad caps CAN take other components with them...so it may be more than just caps...but that's a solid place to start.

[robespierre]

Initial symptom (display takes longer to come on) sounds like a power supply issue indeed. Check the main primary-side capacitors (but be extremely careful to discharge them properly before touching them. They hold deadly charge!)

Is the "high voltage click" a degauss pulse? Do you know what that sounds like?
Is it a relay? You should try to find out where the sound is coming from.

These chassis were not specially designed for SGI, they were based on existing Sony designs. Check if there is a service manual for the GDM-400PS.

[weblacky]

Initial symptom (display takes longer to come on) sounds like a power supply issue indeed. Check the main primary-side capacitors (but be extremely careful to discharge them properly before touching them. They hold deadly charge!)

Is the "high voltage click" a degauss pulse? Do you know what that sounds like?
Is it a relay? You should try to find out where the sound is coming from.

These chassis were not specially designed for SGI, they were based on existing Sony designs. Check if there is a service manual for the GDM-400PS.

PDF service manual (Disassembly, Schematics, etc) for the GDM-400PS is here; https://elektrotanya.com/sony_gdm-400ps....nload.html

I checked this download myself, ZIPPED SINGLE PDF for this model. May I ask how the GDM-400PS model is related to the model that OP asked about?

[PleaseEatEggs]

Initial symptom (display takes longer to come on) sounds like a power supply issue indeed. Check the main primary-side capacitors (but be extremely careful to discharge them properly before touching them. They hold deadly charge!)

Is the "high voltage click" a degauss pulse? Do you know what that sounds like?
Is it a relay? You should try to find out where the sound is coming from.

These chassis were not specially designed for SGI, they were based on existing Sony designs. Check if there is a service manual for the GDM-400PS.

I’ve been using the the manuals for the GDM-4011P and GDM-5411 throughout the entire process, and they are reasonably similar, although neither of them have the flyback transformer on the G board like this one does (GDM-4011P has a similar layout which I use to reference my own parts, and GDM-5411 shares many components). 

I’m not too much of an expert on electrical components, but I’ve uploaded an MP3 file of the sound I heard which can be found here: https://drive.google.com/file/d/1scViV2I...sp=sharing

And if its any use, here are the service manuals I’ve been using so far: https://drive.google.com/drive/folders/1...sp=sharing
(Due to some glitch, I have not been able to erase my notes on the G board in the 4011P file, but that is where I was starting my search)

---

This won't be of direct help, but there are Sony Trinitron-specific guides online (I've seen them), that said CRT technology is actually very complex in the voltages required (not including any adjustments, hopefully you'll require none).  I do have a couple GDM service manuals (not for your model) but they could be helpful.  Likely since it's sa low, slower, symptom...until nothing, you're likely dealing capacitors (fill-time/slower oscillations) changing/degrading.

example:
https://elektrotanya.com/sony_gdm-fw9011...nload.html

Possibly just sign up for this site (it's not easy, he asks quiz questions to prevent most people from applying) but this the best place to get manuals for similar GDM monitors:
https://elektrotanya.com/showresult?what...l&kat2=All

You can do five downloads a day for free, if you don't sign up.

My suggestion would be to unplug it and leave it alone for a while, then you'll need to remove the neckboard and the main PCB under the tube and go through and start writing down the cap physical dimensions, values, and markings, then you can come back and with some help, try to track down OK substitutes.  Dimensions of the cans and values/markings all matter!

If you find one of these service manuals has the same neck board description you'll likely get good test points for voltage tests to check various required voltages.  But I'd assume from your description, it's likely caps, replace them and it's highly likely it will come back to life (no guarantees on picture/image quality).  However there will be many, you'll need a desoldering gun to help prevent delamination, and for caps alone, be prepared for like $100 (or more) just in caps.  Also I'm told bad caps CAN take other components with them...so it may be more than just caps...but that's a solid place to start.

Ah, finally a decent website for these service manuals that doesn’t insist I pay $10 to download the pdf… 

Here is a picture I took of the monitor as I was disassembling it as a reference: https://drive.google.com/file/d/1sccflKP...sp=sharing

The board on the left is the G board, responsible for power. This is the board I removed, and I honestly couldn’t see any visibly broken parts on it (the blue cap by the FBT is just covered in some sort of silicon glue, I’m not sure why), I tested some of the caps, but got a bit overwhelmed after a few. The board on the right is the D board, which should be deflection. Rear board on standoffs is the A board, which has to do with video and output. 

So, would there be caps inside the neck assembly that I should test as well? I’ll probably make myself a list of all the caps on the G board (took a picture of it before reassembly) and check them off as I test them.

[robespierre]

(the blue cap by the FBT is just covered in some sort of silicon glue, I’m not sure why)

Silastic is used to dampen vibrations that could cause the picture to wobble. It is also commonly used to hold the socket onto the CRT neck so it doesn't come loose, and generally as insurance against heavy components working themselves loose during shipment.

Before taking the display completely to pieces, it might be worthwhile to try the WINDAS diagnostic software, which has a Failure mode to report faults detected by the MCU.
You can find more information and links to the s/w here: http://www.piclist.com/images/com/geocit...ua/windas/

[weblacky]

I’ve been using the the manuals for the GDM-4011P and GDM-5411 throughout the entire process, and they are reasonably similar, although neither of them have the flyback transformer on the G board like this one does (GDM-4011P has a similar layout which I use to reference my own parts, and GDM-5411 shares many components). 

I’m not too much of an expert on electrical components, but I’ve uploaded an MP3 file of the sound I heard which can be found here: https://drive.google.com/file/d/1scViV2I...sp=sharing

And if its any use, here are the service manuals I’ve been using so far: https://drive.google.com/drive/folders/1...sp=sharing
(Due to some glitch, I have not been able to erase my notes on the G board in the 4011P file, but that is where I was starting my search)

Ah, finally a decent website for these service manuals that doesn’t insist I pay $10 to download the pdf… 

Here is a picture I took of the monitor as I was disassembling it as a reference: https://drive.google.com/file/d/1sccflKP...sp=sharing

The board on the left is the G board, responsible for power. This is the board I removed, and I honestly couldn’t see any visibly broken parts on it (the blue cap by the FBT is just covered in some sort of silicon glue, I’m not sure why), I tested some of the caps, but got a bit overwhelmed after a few. The board on the right is the D board, which should be deflection. Rear board on standoffs is the A board, which has to do with video and output. 

So, would there be caps inside the neck assembly that I should test as well? I’ll probably make myself a list of all the caps on the G board (took a picture of it before reassembly) and check them off as I test them.

I'm not very good with CRTs (yet) they are low priority and I'd only keep CRTs for CRT-embedded devices (Dumb terminals, Arcades, TVs, etc).  Otherwise I gladly shifted to LCDs for computer displays a long time ago as CRTs really were a necessary evil, not a wanted item.  Yes they can do limited 3D refresh, but that's about all they can do that an LCD cannot. 

So I'm not a CRT collector or anything...In terms of your questions. Well, let's consider your symptoms.  Before the monitor just no longer worked, you got a stable image...right?  Looked fine?  Well then I'd assume (for now) that your neckboard and such as fine and I wouldn't touch them at this stage.  I'd go right for the AC power supply portion of the board, and YES cataloging all the caps is a pain but a needed first step.

What I do is:
Use a sharpie on each cap to number it (I try to use the PCB stencil Number, e.g. C12, if it exists).  Then successfully take lots of pictures will desoldering the caps.  Each cap (once desoldered) should be measured in all height and diameter (if radial-type), lead spacing, the markings on it recorded and decoded, start a spreadsheet with the manufacturer and series as shown on the cap (not always easy!), make sure you record cap orientation on the board (or at least confirm the board markings agree with the orientation you found the cap in!).

You will then research the cap family and use series tables from that manufacturer to identify the family you need to upgrade too (this takes a lot of effort sometimes) from the obsolete family you know have in your hand (original cap).

Then you can purchase your new caps (from research) and apply them to the board and perform tests.

I would definitely test OTHER components on the board as well for completeness before I soldered new caps in (use the empty space left by caps for easier access) and check semiconductors and such.

Keep at it!

[PleaseEatEggs]

Silastic is used to dampen vibrations that could cause the picture to wobble. It is also commonly used to hold the socket onto the CRT neck so it doesn't come loose, and generally as insurance against heavy components working themselves loose during shipment.

Before taking the display completely to pieces, it might be worthwhile to try the WINDAS diagnostic software, which has a Failure mode to report faults detected by the MCU.
You can find more information and links to the s/w here: http://www.piclist.com/images/com/geocit...ua/windas/

Ah, thanks for clearing that up. In the GDM-4011P manual, it mentions a service port on the D board, and after looking at schematics, this is the only connector which isn’t connected to anything on the D board. This might actually be on the G board in my case, but at least now I know what I’m looking for. I’ll buy a cable and try winDAS out, thanks!

Yup, its been years since this thing was fired up (I think it started having problems around 2004, but my dad always wanted to get it back running so its still here), but from what he remembers, the display was perfectly fine. I’ve made myself a little table where I can jot the reference number, part number, capacitance it should have, and capacitance it actually has (I’ll probably test them all for capacitance with a multimeter before desoldering, I’m not too great at it). Thanks for the advice, I’ll let you know how it goes!

[weblacky]

Ah, thanks for clearing that up. In the GDM-4011P manual, it mentions a service port on the D board, and after looking at schematics, this is the only connector which isn’t connected to anything on the D board. This might actually be on the G board in my case, but at least now I know what I’m looking for. I’ll buy a cable and try winDAS out, thanks!

Capacitance test only works OUT of circuit for a multimeter test, don't test in-circuit.  Also all caps will have aged...how much...?  I would just replace everything on the power board...it's been over 20 years so....yeah.

[Raion]

HOLY QUOTE PYRAMIDS BATMAN!!!

Please do not do what this image displays. it makes a mess and it's really not necessary. you can delete the higher level quotes, or else just no need to quote if the person is directly above you (Or use an email-style > indent)

Thanks guys.