exxos's Atari, Amiga & retro forum

rubber_jonnie wrote: 08 Sep 2023 23:25 Unfortunately, I cracked and couldn't wait for your review and ordered a DivMMC Future today too :o

Order shows as 'processing'.

You won't regret your purchase, believe me...

HigashiJun wrote: 09 Sep 2023 00:00

rubber_jonnie wrote: 08 Sep 2023 23:25 Unfortunately, I cracked and couldn't wait for your review and ordered a DivMMC Future today too :o

Order shows as 'processing'.

You won't regret your purchase, believe me...

That's good to hear.

So, I don't have any more T4 replacements to hand, but the rubber feet for the Spectrum + arrived:


So I'll get those fitted and ponder my next troubleshooting steps with the +.

Looking on-line... You did get a 2A transistor for TR4 didn't you, and not just a 1A part? The coil and the caps can cause TR4 to die, but it's usually a 4116 drawing too much juice.

stephen_usher wrote: 09 Sep 2023 15:46 Looking on-line... You did get a 2A transistor for TR4 didn't you, and not just a 1A part? The coil and the caps can cause TR4 to die, but it's usually a 4116 drawing too much juice.

Yes, it was a one for one match with the original. I've got some replacements on order, but they are a different part, I matched up a direct replacement on alltransistors.com since the originals are quite expensive and seemingly only available singly. We'll see how they fare.

In the meantime I tried voltage injection on the 12v rail and took a thermal pic:


The RAM (Row of 8 ICs at the front) is pretty cool, but the LM1889 is very warm in comparison, so I've ordered one of those too. I may try this again, but undo the composite mod, see if it makes a difference.

EDIT: No, removing the comp mod made no change to the LM1889, it lights up like a Christmas tree when injecting voltage on the 12v rail.

Damn !

Your case will melt...

HigashiJun wrote: 10 Sep 2023 11:05 Damn !

Your case will melt...

I really hope the combo of a new TR4 and LM1889 will do the trick, but at present it's the only thing I can see getting warm on the 12v rail, none of the RAM has hotspots, and though I don't have any spare 4116's, I could always press some 4164's into service as that would take the pressure off the 12v line too.

Ok, so I received transistors and am LM1889 today, but didn't get as far as fitting the LM. Why I hear you ask? because for some reason the transistor I fitted (Luckily I got an ammo belts worth, direct equivalent) initially worked and I got a picture. Then it got really hot an let out the magic smoke...

So checking just now I seem to have a direct short on the 12v line (With the old LM1889 removed), though it doesn't seem to be the 16K of RAM. Though it does beep, it just seems to be very low impedance, but it's not a dead short.

Ho hum...

The kind of situation I hate...

BTW, this is probably unrelated to your issue, but have you considered replacing the 7805 voltage regulator with a Traco Power TSR 1-2450 ? Your machine will run much cooler than ever.

I had a Traco Power regulator in my Oric ATMOS and it did wonders...

HigashiJun wrote: 14 Sep 2023 08:45 The kind of situation I hate...

BTW, this is probably unrelated to your issue, but have you considered replacing the 7805 voltage regulator with a Traco Power TSR 1-2450 ? Your machine will run much cooler than ever.

I had a Traco Power regulator in my Oric ATMOS and it did wonders...

IIRC, the regulator or coil are likely to cause TR4/5 to fail. They're good regulators - used them a few times in Spectrums