• Please review our updated Terms and Rules here

Cbm 2001 Pet strange boot

daver2 said:
I have never come across a fault like this myself.

Dave
Click to expand...
Neither have I. And that leaves one feeling a little uncomfortable.

I would have put my money on something external to the IC, such as a Tin whisker bridging pin 1 & 2. If that was the case then the de-soldering in the area would have destroyed it it. We can only rely that he checked this properly as he was asked to do.

There are two methods that could help verify what went wrong:

The removed IC though could be placed on a breadboard with a 5V supply and examined, to try to determine what went wrong with it. Its current drain and logic functions & input currents are easily checked. If on testing, that removed IC turned out to be normal, then it could have been a whisker.

The other method (fault replication), in this case, is after the new IC is fitted, is to; 1) short pin 1 & 2 together as an experiment and 2) try disconnecting pin 14 to see if either of those two things duplicates the fault visible on pin 9 of U2.

Of course once most people find an apparently faulty part and cure it with a new part, they don't often have the inclination to find out exactly why the original part gave trouble and the old part just goes in the bin. But I'm sure if we were doing this repair on our own computer, we would have to know what happened, especially in an unusual case.
 
I was thinking exactly the same thing regarding breadboarding up the potentially faulty IC to see if it really was/is faulty.

Like you say, it would be good to know for sure.

I also use my 'hobby' as a useful guide to the types of faults we can expect to see on our systems at work as they age...

Dave
 
daver2 said:
I was thinking exactly the same thing regarding breadboarding up the potentially faulty IC to see if it really was/is faulty.
Click to expand...
One can test most 74 logic ICs in a programmer quickly and easily. Sometimes you'll just miss the very marginal ones but it helps for a general idea.

In this case I'd brush/sand the pins to clean it of corrosion (and those whiskers?) before checking.

Desperado said:
Unfortunately this old ic is missing for pin 1!!!!! :(
Click to expand...
You can solder a piece of a snapped off component leg if the pin didn't break too close to the case. This happened to me as well unfortunately
 
I am desperate because this thread it arrives to over 1360 posts!!!! :(
Guinnes world record for me???? ;)
 
that's right Dave, I'm desperate and sorry for this very reason ... I disturbed you a lot!
 
I ll update this post when i receive the new ic! Thanks so much and good evening!
 
During the wait... it would be nice to see some dual trace pictures. An oscilloscope is the ideal tool for the current set of scenarios.

I recommend setting CH2 to A15 (i.e. pin 25 of C4)... tweak the settings until you get a single stable cycle on the screen... make sure you are triggering on CH2 and set the vertical scale and offset to put it into the lower part of the screen.

Then add CH1... (without changing the time base or triggering)

Share some screen shots with CH1 on pin2 20, 21, 22, 23 of UD2. Then pins 9, 10, 11, 13, 14, 15, 16, 17 of UD2.

To be clear... leave CH2 connected to pin 25 of C4 for all the measurements.

Looking forward to some nice dual trace screen shots
 
Desperado said:
i ordered some 74ls00 on ebay!!
do you think that when i insert the new ic the computer will work?
Click to expand...
Your computer appears to have had more damaged IC's than most and not only that, some have failed along the way, while you have been looking for various faults. So it is hard to know how many faults are left to discover.

It does seem strange that the pins on your IC's are breaking off so easily, are many badly corroded ?

You should be able to solder a new pin (taken from one of your other dead IC's) to the side of the broken pin 1 on the IC A4 you have removed, even if you have to scrape/file the surrounding plastic down a little around the broken pin.

It would be interesting to put this original A4 74LS00 into your newly installed A4 socket and see if the fault returned.

For example, if it (the bad d2 pin 9 signal) did not return, I would have to conclude there was a physical short between pin 1 & 2 that you did not see or measure that got cleared. If the fault returned that would mean the problem is definitely inside the original IC.

(If for example, there was a fine Tin whisker bridging pins 1 and 2 of that IC, it would likely have fractured and disconnected when you cut the pin 1, whiskers are fairly brittle)

Then you could as an experiment put a new 74LS00 IC in the socket with its pin 14 bent out of the socket, so it did not go into the socket, so that the chip was un-powered. Then see if that regenerated the fault. Also try to short pin 1 and 2 with a metal tool to see if that regenerated the fault on pin 9 of U2.

We would all like to know what actually happened in this case. And there is enough material evidence left to find out, if you do the above.
 
Last edited:
Hugo Holden said:
Your computer appears to have had more damaged IC's than most and not only that, some have failed along the way, while you have been looking for various faults. So it is hard to know how many faults are left to discover.

It does seem strange that the pins on your IC's are breaking off so easily, are many badly corroded ?

You should be able to solder a new pin (taken from one of your other dead IC's) to the side of the broken pin 1 on the IC A4 you have removed, even if you have to scrape/file the surrounding plastic down a little around the broken pin.

It would be interesting to put this original A4 74LS00 into your newly installed A4 socket and see if the fault returned.

For example, if it (the bad d2 pin 9 signal) did not return, I would have to conclude there was a physical short between pin 1 & 2 that you did not see or measure that got cleared. If the fault returned that would mean the problem is definitely inside the original IC.

(If for example, there was a fine Tin whisker bridging pins 1 and 2 of that IC, it would likely have fractured and disconnected when you cut the pin 1, whiskers are fairly brittle)

Then you could as an experiment put a new 74LS00 IC in the socket with its pin 14 bent out of the socket, so it did not go into the socket, so that the chip was un-powered. Then see if that regenerated the fault. Also try to short pin 1 and 2 with a metal tool to see if that regenerated the fault on pin 9 of U2.

We would all like to know what actually happened in this case. And there is enough material evidence left to find out, if you do the above.
Click to expand...
Ok this evening i ll try to do!! :)
 
Hi, i repaired 74ls00 s' leg and i inserted on socket but i have always same bad signal on UD2 pin 9!
Time to wait for new 74ls00! I update this thread when it arrives!
Thanks so much!
 
You must log in or register to reply here.
Back
Top