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IBM Model 5153 CGA monitor repair

N

NotLiable

New Member
Joined
Jun 11, 2009
Messages
6
All,
Cringe along with me when I tell you that my IBM PC/XT's monitor fell backwards off of the tubular rack it was on and dropped about four feet to the concrete floor below. It didn't come back on after that, but inspired by Tezza's (probably simpler) repair of his CGA monitor some time ago, I've decided to at least TRY repairing this, as other than the fact that it's dead, it's in beautiful shape, as is the rest of the system.
I have opened 'er up and checked that the power supply still generates voltages. Suprisingly, nothing visibly appears broken, such as a shattered/cracked CRT. I am an electrical engineer, but I don't have a schematic or service manual for this thing or any experience in monitor repair.
Is someone out there able to assist me in troubleshooting this CGA 5153 monitor? I hope so!

Art
 
NotLiable said:
All,
Cringe along with me when I tell you that my IBM PC/XT's monitor fell backwards off of the tubular rack it was on and dropped about four feet to the concrete floor below. It didn't come back on after that, but inspired by Tezza's (probably simpler) repair of his CGA monitor some time ago, I've decided to at least TRY repairing this, as other than the fact that it's dead, it's in beautiful shape, as is the rest of the system.
Click to expand...

Ouch!!

Yes, I was lucky in that my faulty component LOOKED as if it was faulty, so was discovered simply from the careful visual inspection.

I do have something that might be of help. Download this PDF from it's temporary location here [EDIT 17th Jue, 2009: Link now removed, as it was only temporary]

Good luck!

Tez
 
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Downloadin' the docs!

Downloadin' the docs!

Thank-you all for responding! I am downloading the documents referred to by Jorg and Per. I do already have the PC/XT Hardware Maintenance Service manual, but for the monitor it just included a drawing and a parts list. When I have had a chance to evaluate these two docs I'll post again.

Art
 
Art,

Don't forget my one under my link above. It specifically deals with the monitor. Let me know when you've got it, as it's only in a temporary folder.

Tez
 
Done downloadin' docs, dadgummit!

Done downloadin' docs, dadgummit!

Gentlemen:

I found that one of the links was for just one of two sheets of the monitor schematic; the other was for the tech. ref. manual that includes the monitor schematic. I also was led to the Problem Determination Guide, but I wasn't able to get past step 1 (!), which read "After turning the power switch on, did the indicator light? If not, have the monitor repaired." (My Hardware Maintenance Service manual is worse than that - "Is the power-on indicator glowing? NO - replace the color display." Gee, those are helpful! I do now have the schematics, and thanks to the two aforementioned posters for the links, but it wasn't until I read Tezza's last post that I found what I'd not been able to thus far - an actual "here's how to go about fixing the thing" document. The Sam's repair guide was downloaded minutes ago -- you can remove it, Tezza -- and at first glance appears to be just what I need. Of course, I might still find the CGA monitor irreparably damaged and have to toss it, but at least now I have a shot.

My thanks again to all three of you for your help in this matter. I'll keep you abreast of progress.

Art
 
Hi Art,

Hope you can get it fixed.

Yes, some of troubleshooting sections of the so-called technical manuals of IBM tend to suggest replacement of whole units at the end of the diagnostic process. Not much help when you want to actually FIX the thing.

Most early Apple MAC technical manuals are no better!

Tez
 
Is it worth it?

Is it worth it?

All,

I was able to use the Sam's repair guide provided by Tezza in a limited capacity - I made it through all of the power supply checks (1A through 1G), which proved that my AC mains circuitry and power supply was functioning properly. The next step is a high voltage (25,000 of them there volts) test, with no specific instruction given. It's obvious that this guide was written for someone previously schooled in monitor/television repair and sitting at a workbench with all of the needed tools and equipment handy. Hmm. I was sitting at a workbench, but didn't have a high voltage probe for my Fluke DMM. A new probe costs $167+, while used ones are 25% of that on eBay. Even with the probe, however, (which I'll probably never use again), I'm still left wondering how to "check the CRT HV Anode voltage with a HV probe." Shucks - there are no doubt safety precautions which should be taken; I doubt I just shove the probe into that "suction cup thingy" that's been disconnected from the back of the CRT, if that even is the proper place to "check the CRT HV Anode voltage."

See where I'm going? I doubt that it's economically feasible to take it to a TV repairman, so I either take a crash course in television/monitor repair or drop the once-fantastic CGA monitor into the trash can.

I suspect that the impact of the thing dropping caused internal CRT damage, but of course I don't know for sure. I doubt that hitting the floor caused a resistor to "blow." Even if I fault isolate to the CRT, good luck gettin' one of them there thingies now, right?

Long message, but you fellows have been super supportive. Any further suggestions at this juncture?

Art
 
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You can usually tell that the HV is present by the slight "crackling" sound of the static discharge from the CRT, sometimes you can even feel it with your fingers on the faceplate.

Can you see the filament in the CRT glowing? If not, pull the socket assembly off the CRT and measure the heater resistance (pin 7 and 8, IIRC) with your ohmmeter. If it reads open, there's your problem. It's still possible to buy 370RKB22 CRTs, but setup and alignment can be a bother.

Quite often, when a display loses the battle with gravity, a connection will open up on the circuit board attached to the base of the CRT itself. Take a good look for broken solder joints or traces.

I'll have more when I know where things stand. Compared to a multisync monitor, the CGA is easy.
 
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You fellows are amazing

You fellows are amazing

All,
I was ready to use the monitor for a boat anchor or donate it to the computer junk collection center down the street when Chuck's message came in.
1) No, there's no CRT "crackling." I know what you're referring to. No LED indicator, no CRT glow, no static, nada.

2) Chuck suggested "If no [filament glow], pull the socket assembly off the CRT and measure the heater resistance (pin 7 and 8, IIRC) with your ohmmeter. If it reads open, there's your problem." The Sam's guide showed pin 8 as 126V, pins 9 and 10 as FIL, and pin 11 as 127V. There's continuity between 8 and 9 and between 10 and 11. I'm guessing a two-part filament. If so, it looks like my tube survived the tumble.

3) A few minutes under my fluorescent magnifying bench light this evening revealed the worth of Chuck's last suggestion: "Quite often, when a display loses the battle with gravity, a connection will open up on the circuit board attached to the base of the CRT itself. Take a good look for broken solder joints or traces." WOW! I started with the small board that is attached to the CRT connector, and found that it had been mildly damaged. It's like the board itself made impact and was bent a bit, resulting in a few cracked traces. After smiling and saying, "Aha!" I moved on to the main PC board. Shazam! Same thing, larger scale. If I solder on jumpers and redress a few solder points, I believe I can repair the damage.

I'll let y'all know!

Art


I'll have more when I know where things stand. Compared to a multisync monitor, the CGA is easy.
 
Finding and repairing all the cracked connections should get the monitor going, but don't be surprised if the CRT has been damaged. A fall like that can knock the shadow mask loose which will result in an image that looks like a tie dye.
 
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