ZX80 Core - new ZX80 motherboards
Re: ZX80 Core - new ZX80 motherboards
Ok, attaching pin 6 of IC6 to GND still gave 1.4V on reset.
Removing the ROM results in a clean /RESET signal. So it's in this area that the problem must lie.
I'll continue to investigate, enjoy your holiday and again many thanks for the help
Edit: Found that Pin 19/D7 on the ROM is the culprit (shorted to /CLK). Just need to find the location of the short...
B
Removing the ROM results in a clean /RESET signal. So it's in this area that the problem must lie.
I'll continue to investigate, enjoy your holiday and again many thanks for the help
Edit: Found that Pin 19/D7 on the ROM is the culprit (shorted to /CLK). Just need to find the location of the short...
B
Re: ZX80 Core - new ZX80 motherboards
Smoking gun found...
(larger version: http://farm8.staticflickr.com/7345/1127 ... ed83_k.jpg)
The trace running just below C10 seems to have a manufacturing fault in that it's broken and shorted to the positive leg of C10 itself. This would explain the odd reset behaviour...
Now, next step is to fix it Would anyone have the best advice as to how to fix it? I'm used to repairing broken tracks on non-masked boards such as the ZX81/Spectrum, but haven't tried one of these before...
B
(larger version: http://farm8.staticflickr.com/7345/1127 ... ed83_k.jpg)
The trace running just below C10 seems to have a manufacturing fault in that it's broken and shorted to the positive leg of C10 itself. This would explain the odd reset behaviour...
Now, next step is to fix it Would anyone have the best advice as to how to fix it? I'm used to repairing broken tracks on non-masked boards such as the ZX81/Spectrum, but haven't tried one of these before...
B
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Re: ZX80 Core - new ZX80 motherboards
Well done on locating the cause of the problem
As the tracks on the ZX80CORE boards are very fine, I would suggest that you replace the trace by running a thin insulated wire to completely by-pass the trace on the underside of the board. Ideally run it from a pad to a pad, if not use a via.
Mark
PS If you cannot work out where it runs, I can have a look at my (still) unpopulated board tomorrow.
PPS Don't forget to cut the shorted part of the track with a sharp knife
As the tracks on the ZX80CORE boards are very fine, I would suggest that you replace the trace by running a thin insulated wire to completely by-pass the trace on the underside of the board. Ideally run it from a pad to a pad, if not use a via.
Mark
PS If you cannot work out where it runs, I can have a look at my (still) unpopulated board tomorrow.
PPS Don't forget to cut the shorted part of the track with a sharp knife
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: ZX80 Core - new ZX80 motherboards
Ok, short to C10 cut and, given that the errant trace is the D7 line, it looks like the termination point for the trace is the left side of R9. So one very quick patch wire later....
It's Alive.....!
More debugging tomorrow (haven't checked the keyboard nor entered a program yet), a celebratory G&T is in order tonight
Thank you Mark and Pokemon, you've both been of massive help!
B
It's Alive.....!
More debugging tomorrow (haven't checked the keyboard nor entered a program yet), a celebratory G&T is in order tonight
Thank you Mark and Pokemon, you've both been of massive help!
B
Re: ZX80 Core - new ZX80 motherboards
As Mr. Burns would say:
Excellent.. Excellent!!
Excellent.. Excellent!!
Re: ZX80 Core - new ZX80 motherboards
balford, so how many shorts did you find in the PCB ?
inaki.
inaki.
Re: ZX80 Core - new ZX80 motherboards
Just two - first between /CLK and GND on the edge connector, and then the malformed track routing D7 to C10.
To be fair, PokeMon does advise that the tinned portions of the board be inspected thoroughly for shorts. I just forgot to check the edge connector for about a day or so
The malformed track issue seems to me to be a complete fluke, I've just been very unlucky I would imagine. However looking back, I've learned much more about the workings of the ZX80 this way. It's no fun if it's easy, right?
B
To be fair, PokeMon does advise that the tinned portions of the board be inspected thoroughly for shorts. I just forgot to check the edge connector for about a day or so
The malformed track issue seems to me to be a complete fluke, I've just been very unlucky I would imagine. However looking back, I've learned much more about the workings of the ZX80 this way. It's no fun if it's easy, right?
B
Re: ZX80 Core - new ZX80 motherboards
Of course, I am not interested in machines that work at first try!
Said this, I do not like these opaque soldering mask. I prefer the transparent ones.
inaki.
Said this, I do not like these opaque soldering mask. I prefer the transparent ones.
inaki.
Re: ZX80 Core - new ZX80 motherboards
Well I am surprised as well - and I think I can view in on your picture you posted.balford wrote:The malformed track issue seems to me to be a complete fluke, I've just been very unlucky I would imagine. However looking back, I've learned much more about the workings of the ZX80 this way. It's no fun if it's easy, right?
B
It seems to be a small short on the top layer between the wire (marked red/blue in the attached picture) and the right (+) pin of C10 (reset line).
I am not sure how this could happen as it is covered with white paint.
Maybe a failure when the boards have been exposured and acid-treated after.
I am glad you found it and your board is hopefully working now.
- Attachments
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- Clipboard02.jpg (90.89 KiB) Viewed 3664 times
Re: ZX80 Core - new ZX80 motherboards
Hi Pokemon,
Yes, everything is fully working now, and I've had a few good days of use so far. Delighted with the end result
Also, I'd like to put my name down for a ZX80NMIX when they're available if that's okay.
Thanks again!
B
Yes, everything is fully working now, and I've had a few good days of use so far. Delighted with the end result
Also, I'd like to put my name down for a ZX80NMIX when they're available if that's okay.
Thanks again!
B