Fixable IBM 5155?

[modem7]

I checked all the capacitors, and all of them gave a reading on the outside legs, but C58 did on all 3 legs. Does this mean it's shorted?

You didn't confirm that all expansion cards have been removed from the motherboard. I'll assume that they are removed.

It sounds like you did resistance checks on the actual capacitors. Your measurement results don't mean that C58 is shorted, because if C57 (being in parallel) is shorted instead of C58, you'd see the same results. It tells us that there is a short on the -12V line, and because C57 and C58 are the only motherboard devices on the line, one (or possibly both) are short circuit. C58 being of the troublesome tantalum type is highly suspect. Try removing it (by desolder, or clip it off) and then see if your problem has gone.

 

[CannedBread]

That appears to have done the trick, with both the P9 and P8 connectors plugged in, the fan comes on and the speaker does one long then two short beeps. Should I put it back together and test the video?

and yes, I removed all the cards, on the motherboard and speaker are plugged in.

 

[modem7]

That appears to have done the trick, with both the P9 and P8 connectors plugged in, the fan comes on and the speaker does one long then two short beeps. Should I put it back together and test the video?

An early post of yours shows that C8 on the CGA card is damaged. It might be short. If you haven't already removed C8, then do so. If/when C8 is removed, then yes, I'd say it's time to see if it all works when reassembled.

 

[CannedBread]

After removing C8, I put everything back in the case and plugged it in, but no text comes on the screen. Just a very faint line about 1/3 down from the top of the CRT. Does this mean the CGA card is still broken or the CRT? It's too faint to get a picture of.

 

[mikey99]

How does the internal display attach to the CGA card ? I recall its through a small cable
that attaches to a header (pins) on the CGA card. Make sure this cable isn't damaged and
is oriented correctly. Do you have access to any other PC where you could test the CGA card ?

Also, the IBM CGA card has a composite video output connector that could be attached to
a TV or other device with a composite video input.

 

[ibmapc]

How does the internal display attach to the CGA card ? I recall its through a small cable
that attaches to a header (pins) on the CGA card. Make sure this cable isn't damaged and
is oriented correctly. Do you have access to any other PC where you could test the CGA card ?

Also, the IBM CGA card has a composite video output connector that could be attached to
a TV or other device with a composite video input.

There is a four pin header, with one pin (2nd from the top) removed for keying, that is used for an RF
modulator and is also where the cable for the 5155's monitor connects. Unless the the 3rd pin from the top is missing, then the cable to the monitor can only connect in one direction.

To OP
To bad you're accross the pond from me. I have a spare CGA card that I would be willing to loan to you for testing purposes, but I fear shipping would not be cheap. If you would like to look into the cost of shipping from Oregon, USA to your location, maybe something could be worked out. To be honest, that "faint line" sounds like a fault in the monitor, not the CGA card.

 

[modem7]

Also, the IBM CGA card has a composite video output connector that could be attached to a TV or other device with a composite video input.

Also, for those who have a CGA monitor, hooking that up to the CGA card's external 9 pin connector will show video on the monitor.

There is a four pin header, with one pin (2nd from the top) removed for keying, that is used for an RF modulator and is also where the cable for the 5155's monitor connects.

As circled (or should that be "ovaled") below:

 

[CannedBread]

When I took the CGA card out and turned it on, the CRT lit up:



Does this mean the CRT isn't broken?

 

[ibmapc]

When I took the CGA card out and turned it on, the CRT lit up:

View attachment 9306

Does this mean the CRT isn't broken?

Nope. That's how it looks without an incoming signal(nothing attached).

 

[modem7]

Confirm that switches 5 and 6 on the motherboard are set per:
5 = on
6 = off

 

[CannedBread]

Aha! switch 6 was on. I turned it on, and now it counts up the memory

Not quite fixed yet I fear, it gets to 256kb, and then resets. Is it to do with the expansion board (I think that's what it is), or are the switches still wrong?

Switches are:

1 = on
2 = off
3 = off
4 = off
5 = on
6 = off
7 = off
8 = on

 

[marcoguy]

If that is the same as a 5160 mobo, switch 1 needs to be off or it will put it in a loop test (Exactly what it's doing, by the sounds of it)

 

[ibmapc]

Aha! switch 6 was on. I turned it on, and now it counts up the memory

Not quite fixed yet I fear, it gets to 256kb, and then resets. Is it to do with the expansion board (I think that's what it is), or are the switches still wrong?

Switches are:

1 = on
2 = off
3 = off
4 = off
5 = on
6 = off
7 = off
8 = on

Switch #2 is suspect. Do you have a math coprocessor?(8087) If not, #2 should be on for "dissable"

 

[Ole Juul]

Marcoguy and ibmapc are both right. But for goodness sake, there is no discussion or arguing about these switch settings. You set them for what you've got and leave them alone.

 

[marcoguy]

As far as switch 2 goes, I have messed with that switch multiple times and found that it doesn't really matter if you don't have a 8087. The only time it matters is that if you have an 8087 installed and the switch set to disabled, you can't use it.

 

[CannedBread]

hurray

hurray

It works, hurray! Thank you all for helping :D



The only problems now are that it doesn't seem to pick up the additional memory from the Quadboard (it counts to 256KB), so I assume that doesn't work (the only visible problem is a corroded battery, and a DIP switch I messed with). Also, the 1 key on the keyboard doesn't work, but it does on the numpad (I just hope I don't kneed an ! any time soon!). But other than that, it works fine

What should I do about the capacitors I removed? I suppose I can replace them with modern ones, but does anyone know the type they were? I removed C58 on the motherboard and C8 on the CGA card. Thank you again for helping

 

[modem7]

The only problems now are that it doesn't seem to pick up the additional memory from the Quadboard (it counts to 256KB), so I assume that doesn't work (the only visible problem is a corroded battery, and a DIP switch I messed with).

Possible causes:
1. DIP switch settings on Quadboard are now wrong (likely because of your, "and a DIP switch I messed with").
2. Failure of one the Quadboard's RAM chips.

The RAM related switch settings for the Quadboard are controlled by SW1 (switch 1) - shown at http://www.minuszerodegrees.net/images2/quadboard_switch1.jpg
Try setting Quadboard SW1 to ON/OFF/ON/ON/ON/ON/ON/ON (start at 256K, populated with 256K of RAM).

(the only visible problem is a corroded battery,

You need to remove that battery before it does damage.
The purpose of the battery is to keep the real time clock on the Quadboard going (ticking) when the 5155 has no power.

Also, the 1 key on the keyboard doesn't work,

Try removing it (it pulls out) and then putting it back in.

 

[modem7]

What should I do about the capacitors I removed? I suppose I can replace them with modern ones, but does anyone know the type they were? I removed C58 on the motherboard and C8 on the CGA card. Thank you again for helping

I've confirmed that both capacitors are 10uF/16V 3-legged tantalum with negative-positive-negative pin configuration.
They are available at Mouser Electronics:
Mouser part number is 80-T398E106M16AT
(Kemet part number is T398E106M016AT)

Alternatively, you can use 2-legged 10uF/16V tantalums if you observe correct polarity - positive leg into positive hole and negative leg into negative hole.
2-legged tantalums will be easier to locate.

 

[CannedBread]

I had to fiddle around with the 1 key, but it works now. I removed the battery (pulled it out), and set the switches as you said, but when I turn it on it says:

301
256 KB OK
ERROR. (F1 TO RESUME)

f1 didn't do anything.

After booting a couple of times, it now just counts to 256 as normal.
I think the battery had been bad for a long time, and it doesn't look good...

 

[ChrisCwmbran]

I would think that is saveable. It only appears to be a single track on the PCB that is really damaged.

I'm sure that someone here can advise better than me, but I'd think either with care and the use of some conductive paint that you could fix that.

If you follow that track and check the continuity between either end does it still work?

I suspect that the battery damage there isn't why that board isnt working though.

If I recall correctly, isnt a 301 error a keyboard error?