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 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
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.
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 wrote: ↑Tue Jun 16, 2020 5:14 pm
One electrolytic is decoupling the +9V rail and the other provides the timing (with a resistor) for the reset to the Z80.
Mark
Swapped out the regulator and caps and is now rock solid. Many thanks for your help.
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.
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?
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.
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 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
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 playing
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