Another dead A4 (resurrected)

Arc/RPCs, peripherals, RISCOS operating system & ARM kit eg GP2x, BeagleBoard
Post Reply
Boydie
Posts: 396
Joined: Sat Oct 24, 2015 8:25 am
Location: Sunny Wigan
Contact:

Another dead A4 (resurrected)

Post by Boydie » Sun Nov 17, 2019 6:05 pm

I think I know what the answer's going to be, but I'm going to ask anyway, just in case before I start...

A couple of years ago, my A4 was working. I removed the battery before it could leak and soldered a couple of flying leads in its place. When I reassembled it, it no longer worked. So I boxed it back up and forgot about it. Until now.

I opened it up and discovered one reason why it wasn't happy - one of the keyboard connectors had come out. #-o

Now, at best it will come on with Caps and Num lock lights responsive, the floppy light flashes once and moves the head in the standard "I'm alive" way, and there are various "I'm doing something" clicks from the speaker, and the HD will click once after about 10 seconds as if something's trying to access it. CTRL-Break will reset it.
The display, however, is dead. I've connected an external monitor, and the best that will show is a blank (but not completely black) screen; sometimes the monitor's display will announce 640x480, but still blank.
External keyboard brings nothing new.
There are no floppy POST codes reported.

Power-on CMOS reset does nothing. Indeed, turning on with any key held down makes the machine hang with all 3 keyboard LEDs lit up until the reset button is pressed.

After being switched on for a while, it gets less healthy. The external display becomes completely black in a no-input-whatsoever sort of a way. The reboot floppy seek stops happening, and the keyboard LEDs may or may not illuminate. So it fails progressively earlier...

I'm 95% resigned to replacing all the caps on the motherboard but before I go down that route I just want to make sure that there's nothing else I ought to be looking at first.
Last edited by Boydie on Sun Dec 01, 2019 4:35 pm, edited 1 time in total.

RobC
Posts: 2768
Joined: Sat Sep 01, 2007 9:41 pm
Contact:

Re: Another dead A4

Post by RobC » Mon Nov 18, 2019 12:27 pm

It might be worth reflowing the IOC connections. I've found this cures the infamous freezing problem and might help your machine.

I used some no-clean flux in a syringe and then touched each pin with an iron.

Might not be relevant but I found that you can't set the monitor type on start-up (using the keypad) via an external keyboard.

philpem
Posts: 156
Joined: Fri Apr 04, 2014 5:42 pm
Contact:

Re: Another dead A4

Post by philpem » Mon Nov 18, 2019 11:09 pm

Even if you reflow the IOC, I'd still suggest doing the recap -- and clean the board thoroughly with deionised/distilled water followed by 99% isopropyl. Get some of the black antistatic (ESD-safe) brushes and use those to give the board a fair old scrub.

Be careful as the electrolyte tends to lift pads off the board.

Boydie
Posts: 396
Joined: Sat Oct 24, 2015 8:25 am
Location: Sunny Wigan
Contact:

Re: Another dead A4

Post by Boydie » Tue Nov 19, 2019 2:55 pm

Thanks. I’ll get the caps ordered and report back.

Boydie
Posts: 396
Joined: Sat Oct 24, 2015 8:25 am
Location: Sunny Wigan
Contact:

Re: Another dead A4

Post by Boydie » Wed Nov 20, 2019 7:09 pm

Okay, so all caps removed. A few were a bit ropey and had leaked.
Five pads came off - C19 west, C89 south, C134 both, C65 east. Everything else seems relatively unscathed.

What’s the best way to repair these?
89B24588-A71A-4825-AEB2-E6AA25B5CD25.jpeg

philpem
Posts: 156
Joined: Fri Apr 04, 2014 5:42 pm
Contact:

Re: Another dead A4

Post by philpem » Thu Nov 21, 2019 2:44 am

Boydie wrote:
Wed Nov 20, 2019 7:09 pm
Okay, so all caps removed. A few were a bit ropey and had leaked.
Five pads came off - C19 west, C89 south, C134 both, C65 east. Everything else seems relatively unscathed.

What’s the best way to repair these?

89B24588-A71A-4825-AEB2-E6AA25B5CD25.jpeg
Oh, you're in for some fun...

Before I answer your question -- it looks like you have a bit of what could be battery corrosion around B1, C19, etc. I'd put a bit of distilled malt vinegar on there and make sure any battery 'acid' (actually an alkali, usually potassium hydroxide) is neutralised. Repeat the washing (distilled water followed by isopropyl).

Now to fix the pads...

The easy way to fix the pads is to run wires to the nearest via - RoadRunner or wire-wrap depending on the size of the via. That should be easy enough for C19, C65 and C89, but for C134 you have no pads and thus no mechanical support.

The way I did it was to cut out new pads from copper foil tape, tin them, then glue them to the PCB with Araldite. IPC 7711/21B covers it, "lifted land repair", or there's a summary here: http://www.circuitrework.com/guides/4-4-1.html
It's a fairly tedious process and it'll take about 24h for the epoxy to properly cure.

Boydie
Posts: 396
Joined: Sat Oct 24, 2015 8:25 am
Location: Sunny Wigan
Contact:

Re: Another dead A4

Post by Boydie » Thu Nov 21, 2019 7:25 am

Thanks. I’ve already neutralised the battery gunk with acid and gentle brush scrub, followed by distilled water and ipa. Hopefully all that’s left is residual staining/corrosion that won’t progress.

I suspected running wire wrap to the vias was the way to go, and was wondering about doing the same with C134, plus a small blob of hot melt glue to hold it in place. May still be an option if I’m too clumsy to do new pads ( I’ve got two left feet - one on each wrist!)

mattdy4
Posts: 80
Joined: Mon Feb 26, 2018 11:18 am
Location: Wolverhampton
Contact:

Re: Another dead A4

Post by mattdy4 » Thu Nov 21, 2019 9:13 am

There are some tricky YouTube tutorials on how to cut your own copper pads and glue them to a board. Luckily I've only ever lifted a few pads rather than removed and those were then just re-glued down and continuity checked etc. Personally I'd use a rapid Araldite now

Boydie
Posts: 396
Joined: Sat Oct 24, 2015 8:25 am
Location: Sunny Wigan
Contact:

Re: Another dead A4 (resurrected)

Post by Boydie » Sun Dec 01, 2019 3:51 pm

Well, in a major break with tradition, the repair not only worked but has done so first time! Isn't that one of the signs of the apocalypse?

At first the HD looked like it had died from the shock, but a quick thump of the "it's dead anyway, so what have I got to lose" variety seems to have unstuck it and even that's working.

Now all I need to do is source a new brightness button and everything's good.

As always, thanks for the help folks. =D>

RobC
Posts: 2768
Joined: Sat Sep 01, 2007 9:41 pm
Contact:

Re: Another dead A4 (resurrected)

Post by RobC » Sun Dec 01, 2019 6:04 pm

Well done =D>

CJE have the buttons but they are not cheap: http://www.cjemicros.co.uk/micros/indiv ... -A4CBKNOBS

mr-macrisc
Posts: 402
Joined: Wed Feb 07, 2018 3:35 pm
Contact:

Re: Another dead A4 (resurrected)

Post by mr-macrisc » Sun Dec 01, 2019 7:11 pm

An Olivetti laptop may also be a source for a button?

RobC
Posts: 2768
Joined: Sat Sep 01, 2007 9:41 pm
Contact:

Re: Another dead A4 (resurrected)

Post by RobC » Sun Dec 01, 2019 8:15 pm

mr-macrisc wrote:
Sun Dec 01, 2019 7:11 pm
An Olivetti laptop may also be a source for a button?
Yes - the Olivetti A12 and the Triumph Adler Walkstation share the same case as the A4.

The CJE page also mentions that the button "screws into the rheostat" and part of the button will have been left inside. Sounds like it may be easier to replace the rheostat too.

Post Reply