PC XT displays nothing

[mjuergens]

Hello! I'm Mike. Have a PC-XT I acquired back in the 90's, been mostly in storage since then, last fired it up 10 or more years ago I think. Anyway, thought I'd play with it again. Well, this is what I see on the 5151 monitor. Clearly no data is getting to the screen for some reason. The machine seems to act right on power-up, after a little over 20 seconds it emits 1 beep, tries the floppy drive, then accesses the hard drive. But nothing ever happens on the screen. I suspect the monitor, just because I figure it might be more sensitive to the shocks of riding out several moves. I have removed and reseated the video card.

As far as repairing the monitor, I'm not any kind of electronics tech, but I can solder, can remove and replace, might be able to find and repair a broken solder joint....

Is it feasible to get the existing card to drive a modern monitor, one with a 15 pin connection?

Grateful for all helpful suggestions.

 

[twolazy]

Check the tantalum caps on the MDA card for shorts.

 

[modem7]

Check the tantalum caps on the MDA card for shorts.

If a capacitor was short-circuit, it would overload the power supply, resulting in the power supply not outputting any voltages, in which case, the motherboard would not be operating at all. But we can tell from what the OP wrote that the motherboard is operating. It is even initialising the MDA card.

Grateful for all helpful suggestions.

See the 'SYMPTOM: No video, but a stable raster shows if brightness turned up' section of [here].

Of the possible causes listed there, the contrast control is the easiest thing to check first.

 

[twolazy]

My IBM CGA card had a shorted cap, about inch and a half behind the composite out, which didn't prevent the machine from posting. It just wouldn't show video...

 

[mjuergens]

Of the possible causes listed there, the contrast control is the easiest thing to check first.

Operating the contrast control across it's whole range causes no change in the display.

 

[modem7]

Check the tantalum caps on the MDA card for shorts.

If a capacitor was short-circuit, it would overload the power supply, ...

My IBM CGA card had a shorted cap, about inch and a half behind the composite out, which didn't prevent the machine from posting. It just wouldn't show video...

Looking on the IBM CGA card, all of the tantalum caps filter the +5V, and so it must have been a ceramic cap, not tantalum, that went short-circuit on your CGA card.
Of the ceramic caps, I am sure that you are referring to either C31 or C32.
C31 going short-circuit will result in no vertical sync pulses leaving the DB15 connector.
C32 going short-circuit will result in no horizontal sync pulses leaving the DB15 connector.

But having a look at the IBM MDA card, you are correct in that there is a capacitor (ceramic, not tantalum) that if it went short-circuit, would result in no video out. That capacitor is C3.

 

[Ruud]

Is it feasible to get the existing card to drive a modern monitor, one with a 15 pin connection?

If you think about getting the right connectors and just do some wiring: forget about that.

If the monitor is the problem, just type DIR and hit Enter. If the PC has booted, the HDD should react. Better is to disable the HDD and boot from floppy. In that case any reaction to DIR is more hearable and, if you open the case, more visible. Floppy moves = brooken monitor/cable/video card.

 

[DDS]

I've been in the position of sorting through a stack of graphics cards of various types and no known working matching monitor.

I found a solution in one of these:

MCE2VGA

CGA/EGA/Hercules/MDA to VGA converter with scanline emulator

www.serdashop.com

MCE2VGA V2 - MDA (Monochrome) Hercules CGA or EGA to VGA Converter by Felipe Antoniosi - TexElec

*** We have discontinued the MCE2VGA at this time due to parts costs and we have a better solution now. The RGBtoHDMI is functionally equivalent, but it outputs HDMI instead of VGA. Not only does it offer the same inputs but it has a much cleaner output than the MCE2VGA. If you need a VGA […]

texelec.com

Or to "roll your own"

GitHub - lfantoniosi/mce2vga: MDA/CGA/EGA to VGA FPGA Converter V2.00

MDA/CGA/EGA to VGA FPGA Converter V2.00. Contribute to lfantoniosi/mce2vga development by creating an account on GitHub.

github.com

 

[mjuergens]

If you think about getting the right connectors and just do some wiring: forget about that.

If the monitor is the problem, just type DIR and hit Enter. If the PC has booted, the HDD should react. Better is to disable the HDD and boot from floppy. In that case any reaction to DIR is more hearable and, if you open the case, more visible. Floppy moves = brooken monitor/cable/video card.

Thanks, have to see if I've got a 5 1/4 bootable floppy still. How well do those floppies age, are we getting deterioration as with VCR tapes?

 

[mjuergens]

I've been in the position of sorting through a stack of graphics cards of various types and no known working matching monitor.

I found a solution in one of these:

MCE2VGA

CGA/EGA/Hercules/MDA to VGA converter with scanline emulator

www.serdashop.com

MCE2VGA V2 - MDA (Monochrome) Hercules CGA or EGA to VGA Converter by Felipe Antoniosi - TexElec

*** We have discontinued the MCE2VGA at this time due to parts costs and we have a better solution now. The RGBtoHDMI is functionally equivalent, but it outputs HDMI instead of VGA. Not only does it offer the same inputs but it has a much cleaner output than the MCE2VGA. If you need a VGA […]

texelec.com

Or to "roll your own"

GitHub - lfantoniosi/mce2vga: MDA/CGA/EGA to VGA FPGA Converter V2.00

MDA/CGA/EGA to VGA FPGA Converter V2.00. Contribute to lfantoniosi/mce2vga development by creating an account on GitHub.

github.com

Thanks. Would solve my problem, assuming my MDA board is OK. Diagnosing by swapping parts can run into a bit of money.... Wonder how easy it is to replace cable on 5151. That might be the smallest $ next step.

 

[ozzyrules]

Well, if you hear 1 beep, then floopy boot, It seems that your mda/monitor is not working.
No, you can't use a MDA with a VGA monitor without converters... but you can use a ISA 16-bit VGA card.
Some Trident/Cirrus Logic/Acumos/Realtek VGA cards can work on XT 8-bit slot. Just check that the "16 bit" part of the card, doesn't touch any component on the motherboard.

 

[seaken]

Is this an IBM 5160? Is this the only computer you have of this type? For instance, I have several XT class computers of varying brands and I can swap out cards or exchange the monitors, etc. This will help you narrow down the problem part, if you have the equipment in your collection.

If you have a VGA card that might help but you will need a compatible VGA screen. I have a CGA screen and a CGA card also and can swap those in for testing.

Seaken

 

[mjuergens]

Well, if you hear 1 beep, then floopy boot, It seems that your mda/monitor is not working.
No, you can't use a MDA with a VGA monitor without converters... but you can use a ISA 16-bit VGA card.
Some Trident/Cirrus Logic/Acumos/Realtek VGA cards can work on XT 8-bit slot. Just check that the "16 bit" part of the card, doesn't touch any component on the motherboard.

VGA interesting idea. Will see if my oldest other computer, a Windows 95 386 machine (I think) has a vga card I can try. But I note seaken's comment that I need a 'compatible' vga screen....

 

[mjuergens]

Is this an IBM 5160? Is this the only computer you have of this type? For instance, I have several XT class computers of varying brands and I can swap out cards or exchange the monitors, etc. This will help you narrow down the problem part, if you have the equipment in your collection.

If you have a VGA card that might help but you will need a compatible VGA screen. I have a CGA screen and a CGA card also and can swap those in for testing.

Seaken

Alas, no other vintage computers here to aid in troubleshooting. Now when you say 'compatible VGA screen,' do you mean the output of a VGA card in the 5060 might not work with all VGA monitors? What would make a monitor compatible if so? I have no CRT monitors here any more, besides the 5151.

 

[twolazy]

Weird thought, have you opened the machine yet? Perhaps the mono/cga jumper switch is set wrong. Are 5 and 6 set to off?

 

[mjuergens]

Weird thought, have you opened the machine yet? Perhaps the mono/cga jumper switch is set wrong. Are 5 and 6 set to off?

No switches or jumpers have been altered since the machine worked, previously, many years ago....

 

[Chuck(G)]

Okay, I'll drop in here. From the photo, it seems as if you have a monochrome display, probably a 5151, but you haven't identified it, so that's an assumption.
However, that being the case, I can see a raster (as well as retrace lines), so the monochrome card has at least been initialized and is generating sync signals. (this may not be the case with monitors other than the 5151).
First of all, turn down the brightness on the monitor, as you should not be able to see the diagonal retrace lines.
If you haven't opened the system and re-seated the cards and checked the switch settings, do so now.
Then, let's see what you've got. This could be something as simple as a corroded or badly-seated monitor connector.

 

[seaken]

He did say it was a 5151 monitor. But not sure the XT is an actual 5160 or a clone.

Seaken

 

[mjuergens]

Okay, I'll drop in here. From the photo, it seems as if you have a monochrome display, probably a 5151, but you haven't identified it, so that's an assumption.
However, that being the case, I can see a raster (as well as retrace lines), so the monochrome card has at least been initialized and is generating sync signals. (this may not be the case with monitors other than the 5151).
First of all, turn down the brightness on the monitor, as you should not be able to see the diagonal retrace lines.
If you haven't opened the system and re-seated the cards and checked the switch settings, do so now.
Then, let's see what you've got. This could be something as simple as a corroded or badly-seated monitor connector.

Thanks for replying, Chuck. Communication lag (me on total moderation) means you haven't yet seen my recent reply where I mention that in-the-box switches are unchanged from previous working condition. Yes, it's a 5060 and 5151. All cards removed and reset. Monitor has been disconnected and reconnected repeatedly with no variation from current condition. No obvious corrosion issues. My next step is probably to try to check-out the cable from the monitor, see if any of the lines are open.

I'm sort of thinking it's something mechanical (cable or broken solder joint) since it failed during a long unpowered period in which it was moved several times. It was packed up, but still....

 

[mjuergens]

Well, we're going downhill. Opened it up, removed MDA card, took pics of it and connectors, put deoxit on connectors and on board edge, put it back together and tried it. Now the POST gives two beeps and halts, doesn't try the drives. Legend for that post code is "code shown on screen." Of course.

Used to hear it said that you risked breaking something every time you opened one of these things....

Pics, for whatever it's worth, show two views of the end of the monitor cable, the MDA card, and it's connector.