Monitor fried via computer?

[Rubix]

I just got an XT clone which apparently has been stored in an attic for a long time. I connected my IBM 5151 with it and booted it up. The boot sounds of the computer sounded normal, but suddenly I smelled something burning. I immediately turned off the power, but white smoke came out of the computer (not the monitor), together with an awful smell.

The 5151 appears to be dead. Strange thing is, I didn't smell anything coming from the monitor. It doesn't seem to be fried. The computer does, but still works.

Is it possible that I fried the monitor and the graphics card's circuitry by connecting the wrong type of monitor to the computer? I used the 5151 for all standard IBM graphic cards.

Next thing: how to open a 5151

 

[evildragon]

I assume you haven't tested the monitor yet?

The only time I saw a monitor get fried, was because of the scan-rate, and the flyback not liking it.

 

[modem7]

With MDA(monochrome), CGA and EGA, you can certainly damage the monitor by connecting the wrong monitor type to a video card.

Can you damage the video card? There are two combinations I can see that may cause that damage - either an MDA or CGA monitor attached to an EGA card.
In the case of your 5151 (MDA), it grounds pin 2. Pin 2 on an EGA card is 'secondary red', one of the video outputs. Thus with that combination, one of the video outputs of the card is being shorted to ground. It comes down to the design of a particular EGA card as to whether or not that will damage the card.

I think it more likely that the 5151 alone is damaged.

 

[chuckcmagee]

How to open a 5151? Remove the 3 screws on the back of the cover (one lower left, one lower right, one upper middle), slide the whole upper case straight back and up when it clears. Be sure to lose all but the middle screw, everyone seems to pull that one, including me.


Oops, that Magee guy was obviously talking about the computer cover, not the monitor one.

 

[evildragon]

i forgot about the pinouts being different...

On ALL my video cards, I install diodes on the output lines, to prevent any damage to the video card incase of a short.. So far it's worked.. (just don't put diots on the data lines>>VGA cards only)

 

[Rubix]

Thanks

I'm not sure if the video card is damaged. With the smoke out of the computer it seems to be though. I will be on vacation for 2 weeks from now so unfortunately I can't check it yet.

The 5151 has worked on an EGA card, and the B/W parallel card. On a CGA card, it just gave noise, but no damaging happened. I'm afraid the card that fried it is a VGA card, though I didn't have a good look (it was too late for that ).

About opening the case: I get the bottom loose, but the top of the case won't open. I didn't loose all screws though, because the bottom part already opened. But on the bottom of the monitor (not on the back) is really a lot of screws (12 or so). I can't remember seeing any screw on the back of the monitor case. I might give it another try when I'm back home, but I don't want to damage the case.

And yes, I used the monitor before. It's on the photos I posted here.

 

[the xt guy]

An IBM 5151 mono monitor can be quickly destroyed by plugging it into the wrong video card.

A few years ago I read an old usenet post (1999 maybe?) that called the 5151 "the fragile one". It seems that just about all clone mono monitors use the horizontal sync signal just to synchronize a horizontal oscillator stage which then feeds the horizontal output stage. The oscillator circuit always maintains the right frequency. If you feed in the wrong frequency, you'll get an unviewable mess of scrambled, jumpy lines but it won't kill the monitor.

IBM, to make the 5151 as affordable as possible, eliminated the horizontal oscillator stage and fed the sync signal right into the amplifying circuits.

The problem is, the whole horizontal output stage that the signal is being fed into ia a tuned circuit that works at only one frequency, like a tuning fork. It's efficient at that one frequency only. If you try to drive it at another (meaning the wrong) frequency, it will draw a lot of power trying to accomplish that, and burn itself out.

The output of the horizontal stage not only drives the components that move the beam across the screen horizontally, but also the high voltage to produce an image on the screen. When the horizontal output fails, the high voltage does too. Result: no screen image and a hefty repair charge.

The horizontal sync frequencies of a CGA card and a mono card are different. A mono monitor/card uses the frequency of 18,432 hz. A CGA monitor/card is the same as a standard TV, 15,750 hz.

A VGA card is 31,500 hz. EGA varies depending on the resolution (21,850 at 640x350-16 colors; 18,432 at 720x350-4 colors; 15,750 at 640x200-16 colors)

 

[Terry Yager]

IIRC, the monitor has a couple of screws in the top, hidden behind the small removable panels, which must be pried up with a small screwdriver or similar tool. Confirmation, anyone? (I don't have one handy to check, and it's been awhile).

--T

 

[nige the hippy]

I'm pretty sure that's right, the panels lever up only one way I think.

Regarding the pretty hefty repair charge, the usual thing is the switching transistor going short circuit, which used to be expensive then, but an equivalent is a couple of quid or so now.

Don't ask me what the equivalent is though!

Actually, if someone could point me in the direction of the schematics, I could probably give you an equivalent

 

[Rubix]

Thanks for the replies! Wow, I've come to realize, it's been 5 years. And the monitor is still not working.
Yep, I got to open the monitor case back then. It's currently back together though.

What does a switching transistor look like?

 

[NeXT]

It baffled me when I first used a 5151 and found no power switch but when fed their proper MDA signal they will turn on and emit their high-pitched squeal.

 

[modem7]

Careful when working inside the monitor. In case you are unaware, there are a number of hazards present.

First, have you proven that the 5151 monitor is faulty, or is it only your suspicion?

You earlier stated that you have MDA, CGA and EGA video cards. The MDA card is the proper card to use. Per earlier posts, a CGA card may damage a 5151. An EGA card will 'drive' a 5151 only if the card is switched to MDA mode.

With the 5151 being driven by an MDA video signal, expect to see the orange glow of the heater within the CRT. Unfortunately, that glow is next to impossible to see if you look down into the 5151 through the top air vents. The glow may be visible that way in a pitch black room - I've never tried it. The glow is definitely visible from within the 5151, via a small side window, as pictured below. If you don't see that glow when the 5151 is driven by an MDA video signal, then obviously that would be a bad indication.

and emit their high-pitched squeal.

Not audible to me. That must be because of my age.

 

[paul]

I almost lost a pristine 5151 due to a running one of those 3Com network card configuration utilities. Although they usually execute fine, this one resulting in wavy fine lines across the screen (perhaps expecting a CGA card?) I wasn't paying attention however until I smelled something burning several minutes later. And there was only the faintest high-pitched squeal.

It seems this is one monitor that should only be left unattended with caution.