exxos's Atari, Amiga & retro forum

I think I really need to get some kind of video cleanup kit for this 128, it's horrible compared to my breadbin C64.

Time to go trawl the interwebs.

mrbombermillzy wrote: 11 Feb 2022 17:20 Although I can't remember the Zombie maze section of Scarabeus having overhead lighting. :lol:

:lol: :lol:

Added feature :lol:

So after playing with the machine a little bit it was obvious that the keyboard needed some work, many of the keys needed to be really pounded to get them to register. These keyboard use a conductive silicon plunger to make a circuit on a conductive paint pad, and I've had pretty good success just going over all the pads and plungers with IPA using cotton wool buds.

Disassembly requires some of the captive keys (40/80 caps & shift lock) be desoldered, then there are 27 screws to remove :shock:

Although not filthy, the plungers seemed to have a layer of grunge on them, it looks like something has been spilt in here in the past:


Anyhow long story short, all the keys are now working really well. Half a pack of cotton buds done in though :lol:

I've been looking for a standard shugart 5.25" floppy drive on ebay, they're going for silly money! I want it to use with a Kryoflux. I remember when we were throwing these in skips in the hundreds. Blimey.

BennehBoy wrote: 12 Feb 2022 19:02 I've been looking for a standard shugart 5.25" floppy drive on ebay, they're going for silly money! I want it to use with a Kryoflux. I remember when we were throwing these in skips in the hundreds. Blimey.

What about buying an old Amstrad PC1512/1640 or something?

They tend to go quite cheaply if you keep an eye out and sometimes you will get 2 drives and the machine for £50.

Good idea!

So I'm hoping some of you clever people can help me out.

I bought a 1571 disk drive from a reputable seller in NL. It arrived today, photo below:


The part sat on top of that is a spare spindle motor for a 1541 that I'll be working on next.

I plugged in the drive, switched it on and got nothing.

Fearing the worst I checked the input rating to see it was 220V, but tbh that should work just fine but probably waste a bit more power through the regulators (correct?), it's not a switching supply, but transformer, bridge rectifiers and linear regs.

There's a winding hookup for 240V, using that I also get nothing.

The transformer windings are good and there's 24V AC at the secondary winding terminals. UPDATE, 2 secondary windings, one at 24V and one at 13.6V.

I don't see any voltage across the main filtering caps.

All the bridge rectifier diodes are good.

I've replaced the 4 small electrolytics (with correct polarity) but the ones taken out tested fine.

The 2 big main filter caps test fine out of circuit, and charge up.

I've tested the 7805 & 7812 out of circuit and there are no shorts to ground or between input/output.

The diodes there are also good.

The two bright blue caps C3 & C6 are not shorted, but I've not tested them other than that.

Any ideas what I should check next, I'm not good with PSU's.

Here's a photo of the PSU:

I removed the 7812 completely from circuit to see if I could get the drive logic powered, no change, there's something I'm completely overlooking going on.

EDIT1, tested the 2 blue caps, they're 100nf (Marked 100nS). They come in at about 98nf on the tester with an ESR of ~10ohms - but reading online this seems to be typical?

Can you take the PSU out of the picture completely and power the drive from a bench PSU?

Ha, I wish, remember when I was asking after yours because I wanted to buy one? :lol:

Anyhow, after a lot of frigging about I've narrowed things down, there must be a dodgy joint because during the course of metering everything out the drive sprang into life whilst I probed the output of the rectifier circuit. Initially thinking it was a duff diode/mechanical connection due to short leads on the diodes I replaced them all - which resulted in the drive still not working.

Metering there again the drive sprang into life. Putting a tiny bit of pressure on the board there the drives springs into life... so there's either a duff joint or a break somewhere, will be scoping the board later.