Hi
Well it happened Sunday. Right in the middle of copying
some disk on my Poly 8813, it died. I tried to reboot
but nothing seemed to work.
I tried all the obvious things like swapping the RAM addresses
around on the main RAM boards and swapping RAM chips around on
the CPU board before I realized that I was going to have to
trace it out.
The Poly's have a built in machine video front panel monitor.
With all the boot ROMs loaded, it wouldn't come up but if
I removed one of the ROMs, I was able to get the monitor working.
I did some quick checks of the floppy controller card and
that seemed to work. Placing the ROMs in the extra socket,
I wrote a simple checksum. Again, not problem found. They
all matched my copies that I'd filed away( One should always
have backup of machine ROMs ).
I guess now, I was forced to look at the symptoms and
use that to track down the issues. Something I should have
done from the start but I kept expecting something simple.
I noted that the processor was clearing the video and
starting the floppy but not doing the steps to track zero.
When the ROM was removed, all seemed to work OK so the
basic processor operation was OK. It was something in the
process of getting the floppy read. I reentered the monitor
and was able to write some simple code to verify that, yes,
the controller could step both in and out. Still, this was
were it seemed to be hanging.
A while back, I'd made a listing of the code so I figured
I'd look through that. Following the code, I could see
the video clearing and then the setting up of the disk
access. I could see where the drive was selected and then
there was a wait for delay. Bingo, the timer interrupt
was not happening.
Now I had something to trace down. Following the interrupt
ended me on a daughter card that was tacked onto the CPU
card ( I didn't have the schematic for the daughter card
but it only had 3 chips ). A little more looking and I
found a miss behaving 74LS75. I found a spare on one of my
scrap boards and replaced it.
After about 4 hours, I was back in operation. Why is it
that the latching and flopping ttl parts seem to have such a
high failure rate?
Dwight
Hi Steve
I'd be interested in the case you have. I live in Santa
Cruz CA.
Dwight
>Date: Mon, 13 Sep 2004 00:49:58 -0700 (PDT)
>From: steven <tosteve(a)yahoo.com>
>To: cctalk(a)classiccmp.org
>Subject: AIM-65 black plastic cases for give-away in So Cal.
>
>Hello world,
>
>I have two AIM-65 black plastic cases for give-away.
>You pay shipping only. And also a Snickers bar.
>
>Steve
>
>located near Santa Ana CA.
>
>
>
>
>__________________________________
>Do you Yahoo!?
>New and Improved Yahoo! Mail - 100MB free storage!
>http://promotions.yahoo.com/new_mail
>
>From: "Bill Sudbrink" <wh.sudbrink(a)verizon.net>
---snip---
>
>Another data point plus an "Arg!"...
>Ohio Scientific was quite fond of 2114s (Arg!). It looks like
>the cause of the power supply failure in my C4P is that one of
>the 24K memory cards (48 2114s) was drawing well over spec, even
>though it appeared to be providing reliable memory operation. It
>was populated with the LC (low power CMOS) 2114 chip. According
>to specs on the web, these should draw 40 milliamps max. I pulled
>10 at random. Not one pulled less than 70. Now, I tested them
>with all pins floating other than power and ground and I wonder
>how much difference that makes, but totaling up an average of 75
>per chip gives about what the card as a whole draws when in
>operation. The other card, populated with another vendors 2114s,
>draws over 1/2 amp less when in operation, reflecting about 42
>milliamps per chip.
>
Hi
Floating of CMOS inputs may draw a lot more current. These
are not like TTL in this respect. CMOS inputs will tend
to float until current flows through both the input P and
N channel transistors. This is bad for the parts as well as
drawing current. CMOS inputs should always be high or low
while testing power supply current.
Dwight
Here are the codes for the 8050/8250
http://www.devili.iki.fi/Computers/Commodore/8050/Service_Manual/page_5.htm…
The 6 flashes indicate a failure in the first bank of 2114 memory.
Paul
-----Original Message-----
From: cctech-bounces(a)classiccmp.org
[mailto:cctech-bounces@classiccmp.org]On Behalf Of Dave Dunfield
Sent: Saturday, September 11, 2004 1:27 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Commodore PET disk drive power-up error codes
Hi Guys,
Does anyone have information on error-codes that are flashed by PET disk drives
after power-up diagnostics fail.
I have a drive set which after powerup, enters into a state where it flashes the
POWER LED alternating with both drive LEDs (together) - It repeats this flash
cycle exactly 6 times, then pauses, then another 6 ... forever.
I assume it's a diagnostic failure - Can anyone tell me what it means?
Regards,
Dave
--
dave04a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Vintage computing equipment collector.
http://www.parse.com/~ddunfield/museum/index.html
>From: ard(a)p850ug1.demon.co.uk
>
>> [If it is a 2114, it will be the second one I've found dead in PET hardware
>> over the past month - other was was video RAM in a 4032]
>
>FWIW, I've had _lots_ of 2114s fail. I had to replace all of them in my
>8050 (IIRC, if you hvave multiple RAM errors, you get the flash code for
>the lowest bank first, then when you've replaced those you get the code
>for the next bank, and so on...). I had to replace the video RAMs in my
>TRS-80 Model 3. And the RAM in my HP82163 video interface. And more...
>
>In my experiece the 2114 is one of the least reliable chips ever...
>
>-tony
>
Hi
Compared to the 2111's, the 2114's are really quite good.
Dwight
A contact of mine has a bunch of RA60 packs he'd like to sell. If interested
please contact me offlist.
Jay
---
[This E-mail scanned for viruses by Declude Virus]
I just joined because I have a garage full of old computers that my wife
said, "either do something with them or get rid of them." So I am here
to make a decision, one or the other.
