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Sony GDM500PS - Please HELP: red signal fluctuations
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krytron



Joined: 05 Sep 2009
Posts: 28
Location: Europe

PostPosted: Sat Sep 05, 2009 9:15 pm    Post subject: Sony GDM500PS - Please HELP: red signal fluctuations Reply with quote

Hello.

This is actually monitor with Sun logo that came with SPARC workstation. Its FCC ID is AK8GDM500PS and has fixed cable with 13W3 connector (for Sun workstation) instead of standard five BNC inputs. The other input is of course VGA connector.
The interior drawings, schematic and printed circuit boards completely match Sony's GDM500PS service manual.

I'm stuck with several problems on this monitor, and I'm not a professional.
The first problem is that the picture color changes from normal to bluish (or cyan-like), then after several seconds to minutes it switches to reddish, then back to normal. Reddish-normal-bluish cycles are random and not related to the monitor uptime.
The appearance of those color changes are only somewhat similar to changing color temperature from 9300 to 6500K.
I tried poking A boards and D board with plastic rod, but cannot induce color switching. I was inspired to do so by the solder problem on a very old Sony 1962B monitor, which needed resoldering of three (R, G and B) smaller boards perpendicularly soldered to a bigger board.
Inspecting capacitors visually, I didn't found any signs of bulging or leaking electrolyte. I just hope it isn't the infamous IC007 aka CXA2043Q Shocked

The other problem is that now as I type, I can see ghosts after each line that have shape of '|' or 'l', and there are 8-12 of them. It looks something like this:
l l l l l l l l l l l l l
but the actual spacing is about twice smaller.

The third problem is relay RY501 on the D-board that shorts-out one of the two horizontal linearity coils. After switching from lo-res to hi-res, or switching refresh rate for example, it doesn't produce "healthy snap" sound, but bearly audible "tick". In that case, the image is distorted, of course. Then it suddenly snaps after a few minutes, or hours and image is perfect.
Now what makes me wander is that I have a brand new replacement relay (it's DEC DH1-Q) and when tested with 12V and overvoltage diode it isn't nearly as loud as the one in the monitor. I also have GDM200PS (with broken deflection) which produces "snap" of the same loudness.
I tested the voltage on monitor's relay and it's 11.6V - 11.8V, which should be OK.
Could that relay be faulty and if replaced, would the new one switch as loud as the old relay?


Thanks in advance for any comments, suggestions or pointers.

Regards.


Last edited by krytron on Thu Oct 15, 2009 11:37 pm; edited 2 times in total
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krytron



Joined: 05 Sep 2009
Posts: 28
Location: Europe

PostPosted: Tue Sep 08, 2009 12:49 pm    Post subject: So tough? Reply with quote

Wow, I didn't realize I posted so tough question... Confused

Or, maybe I'm just a dinosaur with the CRT in the "LCD/plasma era"?
But it can't be that all professionals fiddling with bulky CRT monitors or TVs just got extincted over the last few years...

Perhaps I should just yell "Monitor problem - please help" or something similar to get at least one advice.

I don't know where else to ask, does anyone have idea?
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Wed Sep 09, 2009 2:31 am    Post subject: Reply with quote

Not familiar with the specific set but based on your description, the color shift & ghosting may in fact be a problem within the CXA IC? Could you try freezing the IC with freeze spray?--sometimes it is possible to induce the problem within the device by cooling &/or heating the substrate.
On the relay"click"sound, it is not conclusive; could be weak internal mechanism of the relay but in that case, a little tap on the case would certainly have an effect. If you do have a new one, why not replace it? Your voltage reading should be more than enough for activating the coil. Not sure if there is any bulletins out for that model as I no longer have access. Perhaps one of the regulars may be able to check with Sony's database just to see. I'll try to look at the schematic as my new job is taking most of my time away from here.
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Thu Sep 10, 2009 2:21 am    Post subject: Reply with quote

In looking at the schematic, RY501 is sourced with +15V DC.
Is your reading of 11.6~11.8V with relay on or off? Unless there is a misprint, in general, loading a relay on a 15V regulated line should not cause that much drop? Another possibility may be a dried up C536?
As a rule, may want to check all your DC levels as the other problem may also be related to a supply line issue?

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krytron



Joined: 05 Sep 2009
Posts: 28
Location: Europe

PostPosted: Sat Sep 12, 2009 3:06 pm    Post subject: Reply with quote

Thank you for your reply and efforts! Very Happy

There are now several issues raised and I'll try to reply as clearly as possible...
vtech wrote:
Not familiar with the specific set but based on your description, the color shift & ghosting may in fact be a problem within the CXA IC? Could you try freezing the IC with freeze spray?--sometimes it is possible to induce the problem within the device by cooling &/or heating the substrate.

I haven't tried freezing the IC007 as it's quite inacessible if the board is not detached. The tube and yoke are in the way.
But then, if I detach the board from the aluminum carrier/chassis, I don't have a proper means to secure it in a safe position to avoid "incidents", like shortcuts, high voltage arcing from "intimidatingly" looking flyback, etc. (dangerous to board or surrounding living beings Mr. Green).
I'm trying to gather as much info as possible before opening the D-board.

vtech wrote:
On the relay"click"sound, it is not conclusive; could be weak internal mechanism of the relay but in that case, a little tap on the case would certainly have an effect. If you do have a new one, why not replace it? Your voltage reading should be more than enough for activating the coil.

Well, I didn't replaced it because of the reasons you mentioned. The first thing I did was tapping the relay with a long wooden pen, but it didn't snap. I continued hitting it harder and harder (being frustrated) until I induced visible sparking within the relay (its housing is a slightly transparent white plastic - even the coil could be seen).
At that moment I forego the kicking attempts forcing relay to "snap". I become suspicious is it relay, and you just confirmed my suspicions. Confused
The components are tightly packed on the board, so I had to use overvoltge protection diode D511 (in parallel with the relay coil) and place tiny wires underneath anode and cathode to check the voltage.
In more detail, a wire going towards the board and underneath the terminal, then on the other side of it going back off from the board and twisted to make a better contact. Then placed an insulation from a thicker wire on this... quite hard to accomplish.

vtech wrote:
Not sure if there is any bulletins out for that model as I no longer have access. Perhaps one of the regulars may be able to check with Sony's database just to see. I'll try to look at the schematic as my new job is taking most of my time away from here.

I downloaded service manual from here Very Happy:
Code:
http://www.eserviceinfo.com/downloadsm/4270/Sony_GDM-500PS.html
http://www.eserviceinfo.com/downloadsm/4271/Sony_GDM-500PS.html
http://www.eserviceinfo.com/downloadsm/4272/Sony_GDM-500PS.html

No other regular seems to bother with CRTs these days... Sad

----
And now, regarding your second post...

vtech wrote:
In looking at the schematic, RY501 is sourced with +15V DC.

The relay is rated at 12V; from the casing: DH1-Q/12 VDC/10A 250VAC. For the "calculation", please see below...
vtech wrote:
Is your reading of 11.6~11.8V with relay on or off? Unless there is a misprint, in general, loading a relay on a 15V regulated line should not cause that much drop? Another possibility may be a dried up C536?

The reading of 11.6 - 11.8V is with the realay on, whether it did tick, or a loud and healthy snap. When the relay is off, it's 0V.
I can't test C536 with the similar trick as the relay because its terminals are completely inacessible without removnig the board. I would like to remove the board and replace all required components at once (if possible), rather than removing it three or four times.
It's heatsink is so heavy that I could easily rip out some wire in case it's not properly secured.

vtech wrote:
As a rule, may want to check all your DC levels as the other problem may also be related to a supply line issue?

I'll do that, but the +15V power line reads 14.6V - from the improvised hookup to the anode of D511, which isn't reliable (there could be a drop of voltage on the contact with the diode terminal, as I have to pull the wire to get the reading).

Now again the same quote:
vtech wrote:
In looking at the schematic, RY501 is sourced with +15V DC.

Well, the resistance of the relay coil is 275 ohm, and it's connected in series with R544 (68 ohm). This gives:
15V*275/( 275 + 68 ) = 12.026V ~ 12V - as stated on the relay housing... hope the calculation is OK.
This neglects the voltage drop on the relay driver Q509.
I think that's the purpose of R544 - to reduce the operating voltage of relay from 15V to 12V.

One more thing about this relay - it behaves completely randomly: sometimes it "snaps" immediately, or after 10 seconds, or 30 minutes, or 3 hours or even after 3 days. Shocked


There is one more thing I noticed, not related to the relay: the monitor also has "blank frames" (don't know how else to call it). Looks like there is a blank picture for one vertical retrace (sometime just on upper or lower part of the screen, i.e. shorter than one V-retrace).
This flicker occurs much less frequently than color changes but concerns me more, though.

Looks like I've got many gremlins in this one, and it's my favorite monitor. And my older GDM200PS recently lost horizontal deflection. Sad Sad Sad


Thanks again for your efforts and posts. I really appreciate it.

Best Regards.
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minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Sat Sep 12, 2009 4:56 pm    Post subject: Reply with quote

Sounds like bad solder connections, some where. If the picture acts up what does smacking the out side case do?
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krytron



Joined: 05 Sep 2009
Posts: 28
Location: Europe

PostPosted: Sat Sep 12, 2009 5:46 pm    Post subject: Reply with quote

Thanks for the post! Very Happy

minnie wrote:
Sounds like bad solder connections, some where. If the picture acts up what does smacking the out side case do?

Actually, I can't induce color change by hitting the A or A3 board after removing the aluminum cage, but smacking the D-board aluminum shield at the opposite side of FBT almost eliminated ghosting Exclamation Very Happy
I guess it's a good sign. But it must be hit pretty hard.
I'll repeat A/A3 kicking with someone to assist me, as otherwise I must simultaneously watch where to hit the boards and use a mirror to observe eventual color changes on the screen.

Thanks.


Best Regards.
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Sat Sep 12, 2009 6:49 pm    Post subject: Reply with quote

Ok, sure sounds like a combination of bad connection(ghosting effect) and a lethargic relay. Your calculation is correct and the 14.6V is also acceptable for the 15V line which at this point, makes it unnecessary for further voltage checking for a relay issue. Although if/when you decide in changing it, don't forget the C536.
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krytron



Joined: 05 Sep 2009
Posts: 28
Location: Europe

PostPosted: Sat Sep 12, 2009 11:15 pm    Post subject: Reply with quote

It's a very good news to me that 14.6V is acceptable as 15V line and that the chase for relay issue is over. Very Happy I was afraid 14.6V was too low...
I already have C536 on "To Replace" list, as I don't intend to remove the D-board again just to replace yet another dry capacitor.

From what I can tell, this board (D) is exposed to high thermal stress - the big heatsink is so hot that I can't put my finger on it.
The area around relay and a group of 10 electrolytic caps (C536 among them) is also very hot.
Then all of it cools down to room temperature when the unit is switched off... and in winter, it could go even lower than "standard" room temperature.

No wonder that after many On/Off cycles some solder points or caps become dry.

Now I need to try freezing CXA2043Q and tap some more on the A boards to see if "color effects" could be induced to sum things up and heat up my soldering iron. Smile


Thanks again for the reply.


Best Regards.
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minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Sun Sep 13, 2009 6:31 am    Post subject: Reply with quote

Screw that, you can take a maginifying glass and look for bad solder connections on the all ready given board you said you can "tap" and make the picture distort. Replace the cap/caps and solder up what ever you can get at on that board. I never liked freeze spray and never did much. Nothing a good wack ot two doesn't prove.
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