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IBM 5155 Portable won't start

spaghetticode

Member
Joined
Dec 30, 2016
Messages
19
Location
Italy
Hi there, I got this computer a few months ago and today I finally got the chance to take a look at it. I was told the computer was booting but due to a keyboard issue, the boot sequence would stop at a certain point. Unfortunately, this is not the case at the moment.

After powering it up, the PSU fan spins a few times, stops and the computer does not start. If I remove the video card, then the PSU starts, I hear a long beep followed by 2 short beeps (I read somewhere this is consistent with the removal of the video card) and I am able to see the raster on the screen by moving the monitor adjustment pots. My guess is I have a broken video card.

Any PC expert can help me in figuring out what's going on and my options?

Thanks,
Andrea
 
You most likely have a shorted tantalum capacitor on the Video card. I think I've seen C8 on the CGA video card that comes with the 5155 go short. Its near the top of the card near the connector for the internal monitor. I bet if you clip it off and put the card back in, it will fire right up. Failing that, look at Minuszerodegrees.net for some great info and troubleshooting procedures.
 
If I remove the video card, then the PSU starts, I hear a long beep followed by 2 short beeps (I read somewhere this is consistent with the removal of the video card) and I am able to see the raster on the screen by moving the monitor adjustment pots. My guess is I have a broken video card.
If it is an IBM CGA card (the card supplied in the IBM 5155), then per what ibmapc wrote, capacitor C8 on the card is the most likely cause. See the "capacitor C8" link at [here].
 
WOW, amazing! I found that cap shorted, exactly as you predicted. That must really be a common issue with these cards. I am assuming this is a double tantalum cap, I read 10-16 on it and my guess is it's 10uF 16V. Will try to confirm that later browsing the internet. I doubt I can find replacements for it, so I'll probably replace it with two 10uf electrolytic caps I have at hand. Would that be a good solution or should I get tantalum caps for a proper repair?
 
WOW, amazing! I found that cap shorted, exactly as you predicted. That must really be a common issue with these cards. I am assuming this is a double tantalum cap, I read 10-16 on it and my guess is it's 10uF 16V. Will try to confirm that later browsing the internet. I doubt I can find replacements for it, so I'll probably replace it with two 10uf electrolytic caps I have at hand. Would that be a good solution or should I get tantalum caps for a proper repair?

It's a single capacitor, just with 3 pins - I imagine to prevent anyone from inserting it backwards - the outside two pins are the same.
You can use an electrolytic but honestly I wouldn't bother replacing it. I haven't had any issues with my C8 missing.

Diagram of pinout also on minuszerodegrees: http://www.minuszerodegrees.net/failure/failure - 3lt.htm
 
That must really be a common issue with these cards.
It has a history of failure, but I would not call it common. Certainly, enough history to know that if an IBM CGA card is overloading the power supply, C8 is the most likely cause.

There are a couple of C8 failures recorded at [here]. Only a couple because that web page records motherboard failures, i.e. user had failure of both motherboard and the IBM CGA card's C8.

Looking at the circuit diagram for the IBM CGA card, C8 is used to filter the +12V on the card. The card itself does not use +12V. The +12V is being fed to Berg connectors P1 and P2. You will not have anything connected to P2. As for P1, the 5155's CRT unit is connected to P1, however the CRT unit does not use the +12V pin on P1. Therefore, you have nothing using the +12V on the card, and therefore can do without C8.
 
It has a history of failure, but I would not call it common. Certainly, enough history to know that if an IBM CGA card is overloading the power supply, C8 is the most likely cause.

There are a couple of C8 failures recorded at [here]. Only a couple because that web page records motherboard failures, i.e. user had failure of both motherboard and the IBM CGA card's C8....

You can add me to that list. Twice! I had a 5160 and a 5155 both purchased at different times from Ebay and both would not start. So, I bought them cheap , knowing they were non-op, and was thrilled to discover how easy the fix was. Clip off C8 on the CGA card and Good to Go!
 
Today I tested the computer, it finally turns on and I can see some stuff on the video. Now, the computer is not yet fully functional, this is what I see:

301
256KB OK
601
ERROR (RESUME=F1 KEY)

and it beeps 2 times. The unit has no HD, only 2FDD. At a minimum, there's still the keyboard issue to solve. But I'll be opening a new thread for that, as the topic is totally different. Thanks everybody for the insights so far.
 
At a minimum, there's still the keyboard issue to solve. But I'll be opening a new thread for that, as the topic is totally different.
Okay.

From the information at [here], you know that a 601 error is floppy drive related, and some possible causes.

Maybe during transit, some things moved about. Is the IBM 5.25" Diskette Drive Adapter card sitting fully in its slot? Are the connectors on tight?

During the power-on self test (POST), did you see the A: drive light turn on?

The 601 test only uses drive A:
Try swapping the floppy drives so that A: becomes B:, and B: becomes A:
You can do that by simply swapping about the two ribbon connectors at the rear of the drives.
 
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