Search found 11 matches

by swperk
Yesterday, 13:03
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

Here's a photo of my Gigatron now happily flashing its Blinkenlights! Thanks, Marcel!
by swperk
16 Aug 2019, 21:18
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

I'm trying to post a photo of my now happy Gigatron, but I keep getting "HTTP Error.' Is there a filesize limit? Is JPG not allowed?
by swperk
12 Aug 2019, 02:29
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

Good news! After a very educational session with Marcel, we determined the problem to be with the ROM. Marcel sent me a new one, and the Gigatron started right up! Thanks again for all the help, Marcel!
by swperk
27 Jul 2019, 14:35
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

Thanks for the additional info. I've spent the last few hours going over the board with high-power loupes looking for solder bridges, unsoldered or poorly soldered joints, and bent pins, and found nothing wrong. I confirmed (again) that all of the ICs were in the proper places and correctly oriented...
by swperk
21 Jul 2019, 23:40
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

After resoldering everything (again), examining every solder joint with a loupe, and heating and cooling the board to see if the behavior changes, nothing is different. I've captured waveforms from several points, and although most look reasonable, I have found some questionable ones (to me, anyway)...
by swperk
20 Jul 2019, 01:10
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

And something else new: Now when I power up the Gigatron, I get the usual startup display of the 5 LEDs lighting up momentarily, but after a second or so, the pattern on the 4 blinkenlights changes. Sometimes none are lit, sometimes the leftmost one is lit, sometimes the leftmost three are lit, and ...
by swperk
20 Jul 2019, 01:01
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

I've got a scope and a logic probe, and so far here's what I've determined:

Looking at the program counter (U3-U6) I find that PC0-PC7 are counting as expected, PC8 is stuck low, PC9 is stuck high, and PC10-PC15 are stuck low.

Where should I start looking next?
by swperk
20 Jul 2019, 00:14
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

Okay, I'll definitely have another look! What are the chances that there is a defective IC?

If I don't have a logic analyzer handy, what are my other options for testing?
by swperk
19 Jul 2019, 19:58
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

So I did a little more investigating, and I see nice looking pulse waveforms all around the circuit board. Then I checked the cathodes of all of the signal diodes around the instruction decoder (U14), and I found pulse waveforms on all of them except D32 and D33 (cathodes are wired together to U14 P...
by swperk
13 Jul 2019, 23:50
Forum: Kit assembly results
Topic: Gigatron trying to start but doesn't
Replies: 18
Views: 372

Re: Gigatron trying to start but doesn't

Replying to my own post: I just resoldered every IC pin, diode, and bypass capacitor on the board, and the behavior is unchanged. Of course, I also checked for solder bridges, unsoldered or unseated pins, etc. and found none. I'm running out of ideas...

Stan