exxos's Atari, Amiga & retro forum

JezC wrote: 14 Sep 2023 13:10 Careful @rubber_jonnie or @PhilC will be after you for taking over his job .. :fire: :fire: :fire: :hide:

:poke:

JezC wrote: 14 Sep 2023 13:10 Careful @rubber_jonnie or @PhilC will be after you for taking over his job .. :fire: :fire: :fire: :hide:

He's welcome to it Jez, one broken C128 being fixed is enough for me so far.

It's a pity that transistors don't have a standard pinout, even in the same family from the same manufacturer. *sigh*

stephen_usher wrote: 14 Sep 2023 13:50 It's a pity that transistors don't have a standard pinout, even in the same family from the same manufacturer. *sigh*

I know, bloody annoying for sure.

Ok, so tracking through the Spectrum schematic for the +-12v/-5v section and aside from the expired diode, now replaced, everything connects to where is should and appears to be fine.

I lifted one end of some components (Diodes, electroytics) so I could test properly and all seem to be fine. It is suggesting to me that currently, since I get no +-12v or any -5v that the replacement transistors are not up to snuff, despite the fact that they are supposed to be a direct replacement and the datasheets agree (Bar the reversed pinouts).

So I've ordered some ZTX 653s which are specified on the schematic and we'll see how they go.

Fingers crossed the lack of -+12v and -5v hasn't damaged the RAM, though I have some 4164s (And 4256s) that I could press into use if needs be.

But a dead T4 is the prime candidate when these voltages are missing, so yeah...

I'd replace the 4116s anyway if I had enough 4164s as then the 12V only feeds the one chip and the system runs cooler. It also no-longer needs the -5V.

stephen_usher wrote: 15 Sep 2023 12:04 I'd replace the 4116s anyway if I had enough 4164s as then the 12V only feeds the one chip and the system runs cooler. It also no-longer needs the -5V.

I'm definitely considering it and was just looking at the board and thinking 'Have I got enough sockets to fit to it :)

That's a very good shout to get rid of the 4116s, I'm surprised they are still working anyway as I always end up having to replace them.

PhilC wrote: 15 Sep 2023 13:20 That's a very good shout to get rid of the 4116s, I'm surprised they are still working anyway as I always end up having to replace them.

They were working, but as soldered in I have no way of testing. As it goes, I have 8 4164's and more than enough sockets, so I think the 4116's are out, as they were in my TRS-80.

I'll pull them and test, see what they are doing.

PhilC wrote: 15 Sep 2023 13:20 That's a very good shout to get rid of the 4116s, I'm surprised they are still working anyway as I always end up having to replace them.

All the DRAM is removed and there was a 50% fail rate when I put it through the tester. Guess I know what's coming next...