exxos's Atari, Amiga & retro forum

Was great to see your exhibition on Saturday, was intrigued by your TT cart buffer board, could help others with cartridge issues who don't want to delve into the inside of their ST/TT/Falcon.

Have you published the details anywhere github, pcbway or similar? Providing you don't mind of course.

thanks

T'was TR2, a BC337... which had become a resistor.

Swapped it out and the machine is happy with a 9V input.

I'm guessing that with the original power supply the machine would have worked fine with the massive ripple as well as that would have been boosted and then regulated down. So obviously the transistor had blown before I arrived.

jwd wrote: 12 Oct 2026 16:30 Was great to see your exhibition on Saturday, was intrigued by your TT cart buffer board, could help others with cartridge issues who don't want to delve into the inside of their ST/TT/Falcon.

Have you published the details anywhere github, pcbway or similar? Providing you don't mind of course.

thanks

I can't remember if I have or not. As I said on Saturday I'm thinking on respinning the board anyway. I seem to remember that I had to file if down as the cartridge connector was too wide. The next version will latch the address bus which should help with compatibility as well.

stephen_usher wrote: 12 Oct 2026 16:54 T'was TR2, a BC337... which had become a resistor.

Swapped it out and the machine is happy with a 9V input.

I'm guessing that with the original power supply the machine would have worked fine with the massive ripple as well as that would have been boosted and then regulated down. So obviously the transistor had blown before I arrived.

Well that's interesting because TR2 was dead on mine when it arrived and it died again in the run up to CL5.

Mine won't run at all with TR2 dead and I'm wondering if there is a fault in the buck circuit.

TBH I tried running mine on 12v and it got super hot very quickly so I've pretty much been running it on 9v all the time.

I have also been running it via the FDD card so wondering if that's why the buck circuit on that died. I might try running it on separate supplies see if that helps.

I changed TR2 & TR3 on mine whilst I had it out the case but mine still needed other tweaks to stop the boots reen shifting.

Glad you got it sorted though.

rubber_jonnie wrote: 12 Oct 2026 17:02 Well that's interesting because TR2 was dead on mine when it arrived and it died again in the run up to CL5.

Mine won't run at all with TR2 dead and I'm wondering if there is a fault in the buck circuit.

TBH I tried running mine on 12v and it got super hot very quickly so I've pretty much been running it on 9v all the time.

I have also been running it via the FDD card so wondering if that's why the buck circuit on that died. I might try running it on separate supplies see if that helps.

The buck booster is on the PSU side of all the supply voltages. I guess that if you have a PSU which has a wobble on it then it could get into a harmonic resonance with the supply and go over voltage.

If you power your floppy interface from the machine's normal power jack then this is fed straight through to the expansion edge connector, before it gets to the boost circuit.

I'm guessing that this is a normal failure mode and TR2 on the Enterprise is just like TR4 on the Spectrum. At least when it dies it does so without any risk to the rest of the system.

stephen_usher wrote: 12 Oct 2026 17:44
The buck booster is on the PSU side of all the supply voltages. I guess that if you have a PSU which has a wobble on it then it could get into a harmonic resonance with the supply and go over voltage.

If you power your floppy interface from the machine's normal power jack then this is fed straight through to the expansion edge connector, before it gets to the boost circuit.

Ok, that seems reasonable.

stephen_usher wrote: 12 Oct 2026 17:44 I'm guessing that this is a normal failure mode and TR2 on the Enterprise is just like TR4 on the Spectrum. At least when it dies it does so without any risk to the rest of the system.

Yes, it seems that TR2 is the equivalent of TR4 on the Speccy...

But also glad that it doesn't kill the rest of the machine when it goes as BC337's are nice and cheap and readily available.