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IBM 5150 problem: screen garbled

C

Crazy Dog

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Jul 9, 2009
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Hi folks,

I acquired an IBM 5150 computer with monochrome monitor some days ago. After switching the comp on it boots up with some beeps (1 long, 2 short) and then shows an half-garbled screen (screenshot attached). I checked all dip switches on the motherboard and according to the manual everything is correct. The comp has a CGI card. Unfortunately I don't have the diagnostic disk (the comp came without disks).

I would like to get the machine work again properly. I am looking forward to your comments.

Cheers,

Andre
 

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Sounds like one long, two short is your video adapter. Definitely try reseating it a few times incase it's just a bad connection or some corrosion in the slot/pins. Could also be bad video ram which if it has any removable memory chips/dips on the card you could carefully remove them and reseat them too.
 
According to this Wiki article that beep code indicates something wrong with the graphics adapter.

Code: 
Original IBM POST beep codes

    * 1 short beep - Normal POST - system is OK
    * 2 short beeps - POST error - error code shown on screen
    * No beep - Power supply, system board problem, disconnected cpu, or disconnected speaker,
    * Continuous beep - Power supply, system board, or keyboard problem
    * Repeating short beeps - Power supply or system board problem or keyboard
    * 1 long, 1 short beep - System board problem
    * 1 long, 2 short beeps - Display adapter problem (MDA, CGA)
    * 1 long, 3 short beeps - Enhanced Graphics Adapter (EGA)
    * 3 long beeps - 3270 keyboard card

Try pulling the graphics card, blowing it off and re-seating it. Failing which try and put it in another slot.

Another thing is to try and flip the switched (number 5 and 6) since those switches are difficult to read, I thought I had mine set but it turned out they were backwards.
 
barythrin said:
Definitely try reseating it a few times incase it's just a bad connection or some corrosion in the slot/pins.
Click to expand...

I did that already. Also used another slot - same display problem.

Could also be bad video ram which if it has any removable memory chips/dips on the card you could carefully remove them and reseat them too.
Click to expand...

Also I tested if some chips get hot, but everything keeps cool.

Unfortunately everything on the CGI card is soldered :cry:

Are these CGI cards easily available nowadays?
 
Crazy Dog said:
Are these CGI cards easily available nowadays?
Click to expand...

I assume you mean CGA. Check ebay.

Did you try flipping the switches on the motherboard? I had a similar problem with a VGA card in my 5160 and it turned out the switches were backwards and and when I flipped them I did not get them to "click" so they did not really change. Those switches are not as intuitive as modern dips IMO.
 
Check the bottom of the screen, where you would normally tell BASIC to run the program. Makes me think that his video card IS bad.
 
Hi! Considering how its failing, I would take a long look at the memory chips and the decoder logic and/or buffers nearby. "/" is $0F which means the lower nibble is stuck high (ie, the DRAM is not appearing where it should). That says buffer or decoder problem to me.

Considering the ICs are all soldered in, it may be easier and more cost effective to just replace the MDA card with a cheap clone. If the MDA board is worth keeping though it is probably a fairly doable fix.

Please post a clear close up photo of the board.

Thanks and have a nice day!

Andrew Lynch
 
Jorg said:
Erm. Is your "/" key stuck??
Click to expand...

Nope - a stuck key gives you a keyboard error at boot. (a 300 series error) This is definitely a video card problem. And the beep codes are right. I was playing with a 5150 just last week, and plugged in a VGA card. The BIOS apparently doesn't detect it when it probes for it, so it gives off the error beeps, but then the VGA bios itself loads, and the card works perfectly.

And it does look like a video RAM problem. Since you have the mono monitor, you can use either the CGA card or the MDA card if you just want to replace the card, or you could go about fixing the card. IIRC, there aren't any socketed parts on the CGA card except for the ROM. I'm sure Bill will chime in, I know he's fixed a couple of those cards. I guess I've just had good luck, I've never managed to find a bad CGA card.

-Ian
 
RetroHacker_ said:
And it does look like a video RAM problem. Since you have the mono monitor, you can use either the CGA card or the MDA card
Click to expand...

I have only the CGA card that came with the comp. No MDA available, I afraid.

(I tried the dip thingie but no success.)

Ok, here is the part number: 1501985 430 V9116.
 
Last edited:
lynchaj said:
Considering the ICs are all soldered in, it may be easier and more cost effective to just replace the MDA card with a cheap clone. If the MDA board is worth keeping though it is probably a fairly doable fix.
Click to expand...

He could always get a Hercules card to replace the MDA, as he would then have graphics capability.
 
Crazy Dog said:
I have only the CGA card that came with the comp. No MDA available, I afraid.

(I tried the dip thingie but no success.)

Ok, here is the part number: 1501985 430 V9116.
Click to expand...

But 1501985 is the part number for an IBM MDA.

Rreplace U15 (2114-2) and you should be okay. I'd probably replace both U14 and U15 simply because they share everything but the CS/ line. You never know when one bad part can affect the operation of the other.

Happily, 2114's are still available (check eBay). Shouldn't take you more than a half-hour with a soldering iron and a solder snorter.
 
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