rbruinsma
If pin 20 is the clock input to the Z80 (I think that's right), check with your logic probe to see if the heartbeat
exists on the back of the board at pin 20. If not, check to see if you have continuity between pin 20 and the
output of the crystal oscillator. If not you may have to run a wire from the oscillator to the Z80 clock input.
It may be as simple as having to re-flow the solder on the pin-20 connection. I had this exact problem a while back.
Let us know how this goes...
Douglas
On Feb 16, 2013, at 12:12 PM, rbruinsma <rbm...@gmail.com> wrote:
I have a little problem to get my SBC to run. I have read a lot of posts on this form and checked the most things that were suggested in these posts.
The only thing that I can find that is wrong on board is that I have no pulse on pin 20 of the Z80 IC. (tested with a logic probe)
What does that mean? What could I check next?
What I have checked so far:
- pulse on pin 6 of the cpu and pin 16 on the 16550
- VCC on all IC's
- solder work, re-tipped a few
- reburned my rom a few times, no errors and I use the ROMWBW
- tried two different max232: ADM232A and MAXIM 232CPE
--
You received this message because you are subscribed to the Google Groups "N8VEM" group.
To unsubscribe from this group and stop receiving emails from it, send an email to n8vem+un...@googlegroups.com .
To post to this group, send email to n8...@googlegroups.com.
Visit this group at http://groups.google.com/group/n8vem?hl=en .
For more options, visit https://groups.google.com/groups/opt_out .
---
Douglas Goodall, http://goodall.com
Note: I don't use messenger, or skype, or facebook, chat programs in general. Having always-on open communication links through massive public servers I don't have control over seems like too much of an invitation to be infected by a virus or bot. It is bad enough that my Mac wants to stay in periodic contact with Apple's cloud. Skype was tempting before Microsoft bought them. There have been too many examples of remote session links being abused by vendor employees. Even "back to my mac" makes me nervous. There was a recent episode where Apple cooperated with a social engineer and compromised someone's entire electronic persona. If you want to speak with me, calling me on the phone works well, and you don't have to wonder if the electronic mail got through or not. When I say "Hello, this is Doug", you know who you are talking to. Just in case you were curious.