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IBM Fixed Disk Floppy Controller Assy 61-031099-00 Trouble

M

MaTel

Experienced Member
Joined
Jun 16, 2008
Messages
183
Location
Hamburg, Germany
Hello,

I have here an old IBM Fixed Disk / Floppy Controller with Assy 61-031099-00. If this card is inserted into my IBM 5170 I can't switch on my IBM 5170. It shuts down immidiatly after power on. I think, this card has a short.
Where should I start with the troubleshooting?
 
Hi,
I'd start from the tantalum capacitors, if there's any - those are usually across the power lines and tend to go short over time.
 
MaTel said:
I have here an old IBM Fixed Disk / Floppy Controller with Assy 61-031099-00.
Click to expand...
So, the 'Fixed Disk and Diskette Drive Adapter (first generation)' shown at [here].

The circuit diagram is at [here].

MaTel said:
If this card is inserted into my IBM 5170 I can't switch on my IBM 5170. It shuts down immidiatly after power on. I think, this card has a short.
Click to expand...
It sounds like it.

MaTel said:
Where should I start with the troubleshooting?
Click to expand...
First, do a very good visual inspection, because you may be able to see the faulty component.

If that does not reveal the faulty component, then take a look at the earlier thread at [here]. There, a multimeter is used to measure the resistance of the voltage rails on the card. A zero, or very low reading, indicates which rail has the short. From that information, and the circuit diagram, suspect capacitors can be identified.
 
The visual inspecion has not been successful. All compoments looks good. I will do well on the rocky path of diameter :(

Update:
resistance between 12V and ground is 1,1kOhm
resistance between -12V an ground is 0,8KOhm
resistance between -5V an ground is infinitely
resistance between 1. +5V and ground is 85 Ohm
resistance between 2. +5V and ground is 85 Ohm

Does this tells me anything?
 
Last edited:
As suggested earlier, check the tantalum caps for shorts. If one is near 0 ohms, desolder (or cut one pin) and measure again. Still short -> replace it. Do that with all tantalum caps.
 
MaTel said:
Update:
resistance between 12V and ground is 1,1kOhm
resistance between -12V an ground is 0,8KOhm
resistance between -5V an ground is infinitely
resistance between 1. +5V and ground is 85 Ohm
resistance between 2. +5V and ground is 85 Ohm

Does this tells me anything?
Click to expand...
I did the measurements on my card.

+12V: 1 k ohms
-12V: 3 M ohms
-5V: 430 ohm
+5V: 85 ohms

So, significant differences for the -5V and -12V lines.

My measurement for the -5v line is as I expect, because the circuit diagram shows only one component on the -5V line; that is a 430 ohm resistor. You must have measured the -5V line incorrectly.

That leaves your measurement of 800 ohms for the -12V line, compared to my measurement of 3 M ohms. Although not 0 ohms, nor a few ohms, it is suspicious in comparison to my measurement. The circuit diagram indicates that on the -12V line are two op amps and three capacitors (C46, C24, C9). Of those, C46, a large tantalum type, is (my opinion) the most likely to have failed.

That fits with the experience recorded at the web page pointed to by bear.

Per Stone's post, if you cut C46 off the card, does the computer then start ?
 
modem7 said:
I did the measurements on my card.

+12V: 1 k ohms
-12V: 3 M ohms
-5V: 430 ohm
+5V: 85 ohms

So, significant differences for the -5V and -12V lines.

My measurement for the -5v line is as I expect, because the circuit diagram shows only one component on the -5V line; that is a 430 ohm resistor. You must have measured the -5V line incorrectly.
Click to expand...

you're right ;)
a second measurement showed 430 Ohm

That leaves your measurement of 800 ohms for the -12V line, compared to my measurement of 3 M ohms. Although not 0 ohms, nor a few ohms, it is suspicious in comparison to my measurement. The circuit diagram indicates that on the -12V line are two op amps and three capacitors (C46, C24, C9). Of those, C46, a large tantalum type, is (my opinion) the most likely to have failed.
Click to expand...

a second and a third measurement shows 800 ohm between ground and -12V.

That fits with the experience recorded at the web page pointed to by bear.

Per Stone's post, if you cut C46 off the card, does the computer then start ?
Click to expand...

I'll try. But my 5170 is not here to test it. In a few days i will give a answer.
 
Last edited:
Hello,

today I have tested the C46 cap. After I have cutted one pin from the board, the Computer starts normaly. A measurement of this cap... 0,8 Ohm :evil: :D . OK it is definitly shorted.
By the way I soldered also the C45 Cap out ( same CAP as C46 ). After new caps soldered in, the controller starts normaly again and the floppydrives and the harddrive works fine with it.

THANKS TO ALL!!!
 
I just bought a Broken 5170 Computer setup complete last week at a fair price. It has a ton of shorts and doesnt work (including the 5151 monitor). I am so glad I stumbled on this thread as I was having the EXACT same issue as the OP and the C46 capacitor was the culprit shorting out the system. Thats another short fixed on this system.
 
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