Re: A couple of PET drive problems...

From: Bryan Pope (
Date: 2007-04-10 03:38:32

What has gone one with these two issues:

> > 1. I have a 4040 that when powered up the LEDs blink nine times.  I 
> > can't find a flash code table for the 4040 at, but for 
> > the 8050 it says it is the Common RAM, $4000 - $43FF.  Could this be 
> > the same for the 4040?

This was the RAM chips at UF5 and UF4.  After replacing both in 
each of my 4040s, they powered up proprely.  I noticed on one of the 
4040s that a couple of the RAM chips was replaced previously, but there 
was one in the UC column and one in the UD column.  What kind of test 
could they have done to figure out which RAM chip was bad while the 
chips were still soldered on? 

> > 2. With a 2031, it powers up correctly but whenever you try to do any 
> > disk access like get a directory or header a disk, the computer hangs 
> > until I power off the 2031.  I have already swapped the ROMs and the 
> > 6522, but the problem still persists.  I haven't swapped the 
> > 75160 and/or 75161 yet.  Could one of these be the problem and if 
> > so which one should I swap first?  I am trying to minimize any 
> > desoldering/soldering...

This problem *finally* came to the 75161.  After checking logic of 
pretty much the entire IEEE interface part, I thought the problem 
was capacitor C53 had failed was was shorted to ground.  But after 
removing C53 and testing again, the empty space of C53 was still 
shorted.  I then checked pin 8 of the 75161 to pin 20 (ground) 
and found out that they were shorted.  So after replacing this 
75161 this 2031 is happily working again.. 

I have also found out that the $10.50 desoldering iron from 
Radio Shack make removing chips a *LOT* easier and faster.

Thank-you all for your help!



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