msknight wrote: ↑Mon Jan 01, 2024 5:18 pm
Is there any way of telling these substandard parts from the legit ones, perchance?
For semiconductor parts, very careful visual examination of a suspect part, especially the package, markings and any moulding stamps/marks, ideally comparing it side by side with a real/legitimate part. But you do need to know/have experience of the correct details, so you know what to look for.
Electrical testing.
Or the extreme measure of cutting it open so that the actual semiconductor chip is exposed for examination.
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.
I'm more than happy with Woking on PCB's such as this as I'm Head of R&D for the UK's last welding power source manufacturer. But that doesn't mean to say I know everything and having seen various versions of ROM's used in these machines it's best to ask the experts on this site. Especially as this ROM appears to have no bodge wires or lifted pins on it. Should I just go ahead and power it up after the last couple of repairs are done?? Looking at various other posts on ZX80 ROM's it always seems that there is some kind of modification in place.
We use plenty of 7805's in a lot of our PCB's. Normally I specify Ti or ST branded devices. I have plenty of each at home so no worries there. Working with SMPSU's on a daily basis at work, Im not a fan of replacing linear voltage regulators with SMPSU's unless they have an inbuilt crowbar cct. There's always the nasty possibility that if one of these fail the output can fly up to VCC an kill all the logic instantly. Normally this (though not impossible) seldom happens with linear voltage regulators. But it a personal choice.
Anyway I'll finish off doing some minor repairs that I have left and once I'm ready I'll hook up to a TV and see what happens and let you know.
A lot of ZX80 boards have a mask ROM (which is what the board was designed for). But some have an EPROM.
Not many members here have posted details of what their ZX80 has, so it's not possible to know if or what Sinclair actually sent out. We do know that ZX81s were manufactured using EPROMs (along with wiring alterations for the EPROM).
And, you don't know the history of this board. So, we don't know what happened to it, or if any of the parts were changed previously. The EPROM may or may not be original.
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.
Standby alert