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MaTel
May 4th, 2016, 12:09 AM
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?

bano
May 4th, 2016, 12:49 AM
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.

modem7
May 5th, 2016, 02:12 AM
I have here an old IBM Fixed Disk / Floppy Controller with Assy 61-031099-00.
So, the 'Fixed Disk and Diskette Drive Adapter (first generation)' shown at [here (http://www.minuszerodegrees.net/5170/cards/5170_cards.htm#fddda_1)].

The circuit diagram is at [here (http://www.minuszerodegrees.net/oa/OA%20-%20IBM%20PC%20AT%20Fixed%20Disk%20and%20Diskette%2 0Drive%20Adapter.pdf)].


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.
It sounds like it.


Where should I start with the troubleshooting?
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 (http://www.vcfed.org/forum/showthread.php?46593)]. 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.

MaTel
May 8th, 2016, 06:31 AM
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?

Timo W.
May 8th, 2016, 07:31 AM
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.

Stone
May 8th, 2016, 07:56 AM
Sounds like the short is on +5V.

bear
May 8th, 2016, 09:33 PM
Start here. http://typewritten.org//Projects/IBM/7345708.html#1

MaTel
May 9th, 2016, 03:33 AM
Ok, I have ordered the CAPs for C45 and C46...

Stone
May 9th, 2016, 05:33 AM
Ok, I have ordered the CAPs for C45 and C46...Did it start when you removed those two from the circuit?

modem7
May 10th, 2016, 01:19 AM
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?
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 ?

MaTel
May 11th, 2016, 06:53 AM
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.

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.

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 ?

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

MaTel
May 13th, 2016, 12:41 AM
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!!!