Acorn A4 hardware repair

Arc/RPCs, peripherals, RISCOS operating system & ARM kit eg GP2x, BeagleBoard
Ottly
Posts: 125
Joined: Tue Jun 10, 2014 10:34 am
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Acorn A4 hardware repair

Postby Ottly » Tue Apr 03, 2018 3:29 pm

Hi all,

I have a friends A4 laptop which unfortunately blew a decoupling capacitor (went up in flames and smoke). The laptop worked prior to this capacitor blowing.

I've since removed all the can surface mount capacitors and replaced them all. Unfortunately a couple of the pads had been badly damaged by the leaking capacitors so I've had to use wrapping wire to connect them to the closest negative or positive connection

The laptop partially works (boots into supervisor mode). I've had it displaying on an external VGA monitor, however the image was very poor. Could just make out what the text was displaying, but the text was very blurry. Tried connecting up the laptops LCD screen and now no video output is working. I've since disconnected the laptop LCD but still no external VGA output. The laptop switches on and I can hit caps lock, scroll lock and num lock and the various lights will toggle.

Where should I start looking for the problem? Is it likely/possible for the crystal to have failed that supplies a clock signal to the video IC?

I have a Rigol DS1052E oscilloscope and a hobby components logic analyser (8 channel). However as this is all surface mount it makes it difficult to connect a multitude of probes, etc..

Thanks in advance.

Scott.

Ottly
Posts: 125
Joined: Tue Jun 10, 2014 10:34 am
Contact:

Re: Acorn A4 hardware repair

Postby Ottly » Wed Apr 04, 2018 2:15 pm

Hi again,

Well its been an interesting 24hrs. I've managed to resurrect this A4. Looks like the main problem was corrupt CMOS settings. Holding down delete or R on an externally attached keyboard appears to have no effect on this A4 laptop. Managed to get the grainy display back up and typed in configuration setting from copying them from a working A3020. Once I did this the machine was displaying perfectly.

Now comes the task for putting the thing back together. Have a few more surface mount capacitors to replace on the econet module.

Thanks Scott.

RobC
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Joined: Sat Sep 01, 2007 9:41 pm
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Re: Acorn A4 hardware repair

Postby RobC » Wed Apr 04, 2018 3:42 pm

If you've still got the A4 apart, it may be worth reflowing the IOC chip. I've found a few machines that eventually started to hang and this has fixed them. I just apply flux around the chip and touch each pin with an iron.

Also, it's worth giving the board a good clean if the caps have leaked. Others have reported subsequent problems with gunk that has got onto the PCB.