ZX80 Randomly Resets: Fixed
ZX80 Randomly Resets: Fixed
Dear All,
In a fit of nostalgia I decided to dust off my ZX80 an do a composite mod conversion.
All was going very well and I did indeed achieve a 'crispy display' as per instructions.
I put the machine to bed, very happy with myself and went back to it this morning for another session to see if I could remember how to program it.
After about 5 mins of use it has now developed a random reset behaviour.
Any hints on what to check would be gratefully received. I am assuming the on-board regulator as a first port of call.
Kind Regards
Andy
In a fit of nostalgia I decided to dust off my ZX80 an do a composite mod conversion.
All was going very well and I did indeed achieve a 'crispy display' as per instructions.
I put the machine to bed, very happy with myself and went back to it this morning for another session to see if I could remember how to program it.
After about 5 mins of use it has now developed a random reset behaviour.
Any hints on what to check would be gratefully received. I am assuming the on-board regulator as a first port of call.
Kind Regards
Andy
Last edited by anightin on Sat Jun 20, 2020 9:19 pm, edited 1 time in total.
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: ZX80 Randomly Resets
Certainly monitor the +5V to see if it is within specification (4.75V to 5.25V).
By monitor, I mean keep your multimeter connected and wait while watching it until the symptoms appear.
If the +5V is okay, monitor the voltage on pin 26 of the Z80 CPU. This should be at or near the +5V voltage. It’s the reset circuit.
Mark
By monitor, I mean keep your multimeter connected and wait while watching it until the symptoms appear.
If the +5V is okay, monitor the voltage on pin 26 of the Z80 CPU. This should be at or near the +5V voltage. It’s the reset circuit.
Mark
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 Randomly Resets
Thanks Mark, I'll wait until the new Traco Power TSR 1-2450 switch mode replacement arrives from Farnell then start testing -- I had already planned to replace it so I've already taken out the 7805. I might change the electrolytics while I'm there too -- looks like one is on the regulator and one on the reset line. Will report back.1024MAK wrote: ↑Tue Jun 16, 2020 3:25 pm Certainly monitor the +5V to see if it is within specification (4.75V to 5.25V).
By monitor, I mean keep your multimeter connected and wait while watching it until the symptoms appear.
If the +5V is okay, monitor the voltage on pin 26 of the Z80 CPU. This should be at or near the +5V voltage. It’s the reset circuit.
Mark
Regards
Andy
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: ZX80 Randomly Resets
One electrolytic is decoupling the +9V rail and the other provides the timing (with a resistor) for the reset to the Z80.
Mark
Mark
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.
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: ZX80 Randomly Resets: Fixed
Good to hear that it’s up and running again
Mark
Mark
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 Randomly Resets: Fixed
BTW, has anyone used one of these 'Z80' PSUs:
https://www.ebay.co.uk/itm/BRAND-NEW-Si ... %7Ciid%3A1
The reason I ask is that I did the same composite (and regulator) mods to my Jupiter Ace yesterday, as well as replacing the caps. I was using the same PSU as the one on my Z80 above and would you believe it, the Ace reset itself a couple of times whilst I was testing it.
Fortunately I had pin 26 attached to my DVM and it was reading 4.97v and then dropped to 0v and back to 4.97v again.
Could this be something triggering the PSU protection maybe, dodgy PSU, or just a coincidence?
https://www.ebay.co.uk/itm/BRAND-NEW-Si ... %7Ciid%3A1
The reason I ask is that I did the same composite (and regulator) mods to my Jupiter Ace yesterday, as well as replacing the caps. I was using the same PSU as the one on my Z80 above and would you believe it, the Ace reset itself a couple of times whilst I was testing it.
Fortunately I had pin 26 attached to my DVM and it was reading 4.97v and then dropped to 0v and back to 4.97v again.
Could this be something triggering the PSU protection maybe, dodgy PSU, or just a coincidence?
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: ZX80 Randomly Resets: Fixed
No, I have not even seen that type before. I have more Sinclair ZX PSUs than I have Sinclair computers!
It’s more likely that there is an intermittent connection. I can’t remember the current consumption of an Ace, but there is no way that’s it’s anywhere near 1A, and that’s when using a 7805. With a DC-DC switching regulator, the current consumption will be even lower. So I don’t see any reason for the protection system in the mains PSU to be triggered.
I do know that DC-DC switching regulators really don’t like any sparking on the 3.5mm input jack. So I would advise to clean the plug and the socket. Then if possible monitor the “+9V” supply voltage with you multimeter.
Mark
It’s more likely that there is an intermittent connection. I can’t remember the current consumption of an Ace, but there is no way that’s it’s anywhere near 1A, and that’s when using a 7805. With a DC-DC switching regulator, the current consumption will be even lower. So I don’t see any reason for the protection system in the mains PSU to be triggered.
I do know that DC-DC switching regulators really don’t like any sparking on the 3.5mm input jack. So I would advise to clean the plug and the socket. Then if possible monitor the “+9V” supply voltage with you multimeter.
Mark
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 Randomly Resets: Fixed
I swapped the ZX80 PSU out for a ZX81 PSU and no resets so it could have been a dirty socket I guess (and all the PSU swapping has cleaned it up), or a dodgy PSU. I guess I'll need to keep playing1024MAK wrote: ↑Sun Jun 21, 2020 4:17 pm No, I have not even seen that type before. I have more Sinclair ZX PSUs than I have Sinclair computers!
It’s more likely that there is an intermittent connection. I can’t remember the current consumption of an Ace, but there is no way that’s it’s anywhere near 1A, and that’s when using a 7805. With a DC-DC switching regulator, the current consumption will be even lower. So I don’t see any reason for the protection system in the mains PSU to be triggered.
I do know that DC-DC switching regulators really don’t like any sparking on the 3.5mm input jack. So I would advise to clean the plug and the socket. Then if possible monitor the “+9V” supply voltage with you multimeter.
Mark