exxos's Atari, Amiga & retro forum

Can they be welded with a hot knife or soldering iron?

stephen_usher wrote: 11 Dec 2025 15:05 Can they be welded with a hot knife or soldering iron?

The thought had crossed my mind, however they are incredibly thin:


I suspect melting them might be a bit too much and could ruin them, so without spares I'd be wary of doing that. I'll have to investigate other options first I think.

The pic isn't great at showing this but the walls are probably only .5mm thick at best.

Oh, and the LM3086's arrived today, but it's still dead, so I need to start doing some troubleshooting now.

Still just a black screen with a PAL signal. Plugging in carts makes no difference.

The ROM, RAM and CPU boards are all known working, taken from both my 400/800 during their upgrades, so I can honestly say they should be 100%. All voltages are correct at the 4116 RAM BTW and across the rest of the board.

I will also connect a speaker to the onboard connector, see if I can hear any audio.

In case there is an issue with the video out I'll have a look at seeing if there ia a UHF image with my UHF to HDMI adapter, though it may make no difference as the signal is generated in the same place.

Of course there may be other issues I haven't spotted on the mainboard yet.

Hopefully this gives a better idea of the wall thickness on the plungers:


Dimensions in mm.

Maybe some Humbrol liquid poly would do the job ?

HigashiJun wrote: 11 Dec 2025 22:40 Maybe some Humbrol liquid poly would do the job ?

Unfortunately they are some sort of nylon or nylon like material, very hard and shiny and that sort of glue won't cut it I don't think. I may try acetone later, but I don't think it'll work TBH.

On the flip side I sat down and had a good look at it and I think even if I can glue or weld it somehow, they are just going to pop again really easily, so I've decided to just reassemble and use as it is.Some keycaps may be a bit loose

It isn't going to be a machine that sees heavy use, it's mostly for parts and the keyboard is just for testing.

Here it is with the Dragon keys installed:


Not perfect but good enough for Atari testing purposes.

I have also tested the main IC's from my 400 as it's a bit easier to disassemble and it still does the same so it needs proper diagnosis now.

rubber_jonnie wrote: 11 Dec 2025 23:38 Not perfect but good enough for Atari testing purposes.

Indeed, not worth the pain if it's for testing purposes.

HigashiJun wrote: 12 Dec 2025 02:53

rubber_jonnie wrote: 11 Dec 2025 23:38 Not perfect but good enough for Atari testing purposes.

Indeed, not worth the pain if it's for testing purposes.

What's slightly annoying is than my other 800 has a completely different keyboard, one of the Mitsumi membrane type, so making any kind of comparison is off the cards.

It'll do for now :)

So next step is to trace the clock across the boards according to the black screen fault finding flowchart in the service manual. It has a nice chart of what's what:


So whilst I know the CPU was definitely getting a clock, I need to be sure it is going everywhere else it should go.

I suspect the CPU board will be fine, it's the rest that's a concern as the 3.579 Mhz crystal was missing when I got the board and there were other components missing from the mainboard.

So, basically, someone used this as a parts board because they thought it unfixable. That's what it sounds like.

A good challenge. :-)