Sinclair ZX80 / ZX81 / Z88 Forums

Hi

Today I received an Alphacom from eBay, but when it arrived, it had a defective power supply. (The description on eBay said it would turn on, but otherwise not tested. It didn't turn on.)

The supply says: Input AC240V 50Hz Output AC26.8V 1A. When I measure it I get a shift between 0.0V - 0.1V AC.

I tried to find some old power supplys in my basement, but unfortunately they supply DC output.
One is: Input 240V AC Output 22V DC 0.6A
Another one is Input 230V AC Output 24V DC 550mA

Any suggestions?

Hmm I would try this one. 24V AC is not too far from specified 26V AC - so would give it a go.
http://www.ebay.de/itm/222423447396

PokeMon wrote: ↑Tue Mar 28, 2017 11:03 pm Hmm I would try this one. 24VA is not too far from specified 26V - so would give it a go.
http://www.ebay.de/itm/222423447396

I would also take chance on this one, I have just looked inside my Alphacom and the only power reg I can see is the usual 7805 for 5v and a TIP100 Darlington power/switching transistor which I suspect may be there to control current to the printing platen.

Either way please persevere Martin as the printer is a good one with paper readily available.

I assume plug fuse has been checked (not sure if there is an on-board one) mains and output cable checked for breaks etc

I think, if the AC voltage is too low, the thermal print head will produce poor contrast. Some years ago, I was playing about with a non-original supply. Then again, it could have been something else.

Mark

Well 10% less is not that significant I would say.
So you will get maybe only 90% blackness but anyway you could check if the printer is working in general.
If heating is just a resistor (wire) you could try a DC power supply as well and maybe could try optimum with an adjustable PS.
So I would try ...

Sorry, my post was a bit misleading. The supply I tried was a lot less than 24V AC.

Mark

I'm fairly certain that the original power supply was an unregulated transformer. If so, a modern regulated 24V should work just fine. Certainly an unregulated supply isn't going to be accurate to better than 10%.

I would probably like to find one rated for the full 1A output if possible though unless that printer is known to run on less.

I'm trying to open the power supply. Has anyone here tried to do that?

I removed the 4 screws at the bottom, but somehow it seems to be glued together as well. I don't feel like opening it with a hammer but the sides are unmoveable.

Maybe the heat from the transformer, at melted the plastic together.

Big Clive on You Tube sometimes uses a vice to open plastic cases that have been glued closed.

Mark