Tokin (?) 4501U1

[stween]

I received a sight-unseen 1040 STF today, and pulled the cover off to look for obvious badness before powering up.

The PSU is new to me, and is similar to (but different from) the Tokin PSU listed on exxos's PSU page:

PXL_20220205_044059932~2.jpg (348.4 KiB) Viewed 3331 times

Maybe just a 110v variant? I've mostly dealt with SR98s with a plastic separator between the board and the metal frame and this one ... does not have that.

In any case, the exterior of this unit is yellowed and needs a good clean, and some of the shielding is starting to rust. But the board and the PSU are remarkably clean. With the mix of capacitors, maybe the insides of this have been fixed up and this PSU has been recapped?

Something lets out a high-pitched whine when it's running and I'm not sure what. I haven't kept it powered up for long, but it changes pitch depending on activity. A little like high frequency whining my favourite STE does on the audio channel, except it's the PSU or the machine itself that's whining; I've not wired up any audio out at the moment!

[Steve]

I've recapped many PSUs that exhibited a whine sound before, then after the recap the whine goes away. So that's a fairly normal sign for a PSU that needs some TLC, I wouldn't use it until it is recapped.

[stween]

I'll drop another PSU into this before testing further. Interesting to me though; this board & PSU are so clean, and the caps look (to my inexperienced eye) pretty new, not 25+ years old!

[Steve]

Yeah they can look brand new. But you know an un-used capacitor of 20 years age will be worse condition than a moderately used capacitor. They really go bad if they're just sitting. I've even heard of capacitors having a 'self healing' capacity where just powering them keeps them healthy. Not sure if that is true or not.

[rubber_jonnie]

I don't know if you'd read the Tokin section over here: https://www.exxosforum.co.uk/atari/last/ ... .htm#TOKIN

But it is described as, and I quote, "So far this PSU is probably the worst PSU I have come across so far. It would be possible to update the PSU, though as the capacitors are so squashed up with no margin for error, then I will probably not do any fixes for this PSU. I have not seen many of this type so I do not think it is common anyway."

Personally the few Tokin's I've encountered have generally been of a generally poor build quality compared to others, so whilst re-capping (Definitely looks like somebody already tried) is definitely a route you could take, I would make sure you have a load to test it on, because I wouldn't hook it up to an ST without doing so first. Exxos store has suitable load resistors in the store.

I'd probably replace the transistors and rectifier too if going for a rebuild.

You could consider a Meanwell RD-50A, they are really cheap.

[exxos]

I assume its 125v as it's quoted AC125V 2A next to the fuse. So probably why I've never seen one as machine tend to be 230v types.

[stween]

I don't know if you'd read the Tokin section over here: https://www.exxosforum.co.uk/atari/last/ ... .htm#TOKIN

But it is described as, and I quote, "So far this PSU is probably the worst PSU I have come across so far. It would be possible to update the PSU, though as the capacitors are so squashed up with no margin for error, then I will probably not do any fixes for this PSU. I have not seen many of this type so I do not think it is common anyway."

Hah, late last night I power-skimmed to "Overall its a good device, good voltage and current rating" but didn't grok that this is referring to the transistor, not the overall board.

Personally the few Tokin's I've encountered have generally been of a generally poor build quality compared to others, so whilst re-capping (Definitely looks like somebody already tried) is definitely a route you could take, I would make sure you have a load to test it on, because I wouldn't hook it up to an ST without doing so first. Exxos store has suitable load resistors in the store.

I'd probably replace the transistors and rectifier too if going for a rebuild.

You could consider a Meanwell RD-50A, they are really cheap.

Yeah I can load test and I have a meanwell RD50A here also. I actually bought this as a donor machine, hence sight-unseen; I'm likely to take the mount for the PSU and get rid of the original board.

Based on the price I paid, I didn't think the machine would work at all. The case is a little dinged up and I don't trust this PSU, but at first glance the actual computer is in great nick. I'll do a proper teardown and see what it's really like in there.

[stween]

I assume its 125v as its quited AC125V 2A next to the fuse. So probably why I've never seen one as machine tend to be 230v types.

yeah, this is a US machine

[rubber_jonnie]

I assume its 125v as its quited AC125V 2A next to the fuse. So probably why I've never seen one as machine tend to be 230v types.

I've had a fair few STs through my hands, and only ever had one Tokin. Its PCB is in a drawer for spares , with the PCB replaced with something better!

[stween]

Okay, yeah; rigging the meanwell PSU takes all the noise away. The wailing was so pervasive from that old tokin supply that I didn't believe the noise was all PSU

Anyway, neat, got what seems to be a TOS 1.0 STF with red LEDs and a long-button drive. I've never had one so old before!