Having had some time over the weekend to think about options, I realised that rather than spending a very long time, on possibly a hopeless exercise, it might be worth proving that the PCF8583 was really the source of all the problems. I resolved therefore, to try an get the replacement circuit working, in some fashion, and my best ( but ‘dirtiest’ ) option might be to leave the partly installed board in place, with the already connected datalines, and power the circuit off any available 5v line I could find. It wouldn’t be pretty or permanent, but it would demonstrate that any further time spent finding a tidy way of installing this, would ( or wouldn’t ) be a worthwhile investment.

So, I jammed the power wires into the 5V and GND pins of the empty ROM socket and powered on the machine… Holding down the DELETE key I got a flash of a prompt and then dropped into the ‘Desktop’. Success! Smiles all round.

Just to prove that I wasn’t somehow fooling myself, I unplugged the circuit and low and behold, the Acorn powered on but gave no onscreen prompt or sign of activity  – As before.

It looks like I have found the source of the problem. I just need to find the right way to package the circuit and possible invest in a better soldering iron 🙂

 

So I set to work with the ‘to-do’ list from the visual inspection of the board. The easiest item on the list was to try and re-solder the battery, which got done fairly painlessly.

Trying to replace the capacitor, wasn’t as successful. As soon as I tried to try anything with it, it pretty much fell off the board and took the solder pads with it. A quick check of the schematic revealed it to be a decouple capacitor, between the + and GND rails, so I (might) be able to live without it, right??

I got a magnifying glass and examined the CMOS/RTC IC (IC58) and the solder joints and legs were looking quite ruined, very likely from the effects of the battery leak. I decided at that point to ‘bite the bullet’ and replace the whole circuit, once again following RetroKits advice and rebuild the CMOS/RTC circuit on an external stripboard.  I managed to by a through hole version of the PCF8583 IC on ebay, which surprisingly arrived within 48hours and I set to work building the circuit.

At this point I was reminded that my soldering skills have either got worse with lack of practice, or they were never up to much in the first place… After a LOT of cursing and looking at some really horrible solder joints, I had the circuit complete.

So, this is the position I now find myself. I’ve tried to make a tidy job of attaching the circuit to the A5000’s mainboard, but so far its not been very co-operative. I’m not helping myself by having to choose between either a small, but underpowered soldering iron, OR one that produces more heat but is also correspondingly ‘fat’.

Before continuing I need to find a more reliable and tidy way of attaching this circuit to the mainboard without causing more damage than I’m fixing. I’m considering trying to push a pin through the appropriate holes on the board, to give me something more substantial to solder to, rather than trying to get wires to solder to essentially ‘test points’. Hopefully I can have another crack at it over the weekend.

I stripped down the Acorn, so that I could remove the mainboard and then very carefully cleaned, with Isopropyl Alcohol, the area where the Battery had previously leaked. I might have been a little too careful, as the photos make the area look filthy, even after a good wash…

Checking over the board, with the help of a magnifying glass, has revealed a couple of obvious problems.

Firstly, Capacitor C169 looks like it’s cracked, so I’ll need to investigate replacing that component.

Secondly, there are areas of corrosion on components and IC’s. I sat with a multi-meter and started checking the corroded looking pins on the ARM processor, mostly Pins 80 down to 70, and all appear to have continuity to the tracks on the mainboard. As the socket is empty, I’m not currently too concerned that this is the source of the boot problems, but it’s worth checking whilst I’m at it. There are some other components, such as surface mount Resistors and Capacitors, that look worryingly corroded on the connections.

 

From the Retro-Kit page, on restoring A5000’s, similar problems to mine seem to be caused by the RTC/RAM circuit centred around IC58. I found the schematic for the mainboard and checked the connections going to IC58 for continuity the (easy) components such as Resistors. The continuity and resistance checks revealed all was generally OK in the circuit, except for the following:

• The ground side connection on the Battery appears to be bad; probably a dry joint from my previous poor soldering job.
• The Positive power ( pin 8 ) to IC58 doesn’t appear very reliable. This is an area that appears to have picked up the worst of the corrosion, so I’m not completely surprised.

So, from what I’ve seen so far, my ‘to do’ list is:

1. Replace Capacitor C169.
2. Remove the Rechargeable Battery and resolder, but not before:
3. Checking the corrosion to Pin 8 on IC58. Possibly cleaning and/or attempting to bridge any break with some solder or jumpwire.
4. Check for any further damaged components and replace.

 

If I’m really lucky, this may resolve all the problems. I’m not sure I’m that lucky though.

However, I’m currently working on the principle that I should fix all the obvious, visible, problems first and then dig deeper if required.

It’s obvious that the Acorn is in bad shape. Last time I booted it up, I got a prompt, now I’m getting nothing.

I’ve done some initial tests and confirmed that I’m getting power from the PSU, to the mainboard, of the voltages I would expect. I’ve also checked the Voltage across the battery and confirmed that is normal.

At this stage and having done some reading, a few possibilities look like good starting points. All of the possibilities relate to the legacy or damage caused by the battery having leaked.

Firstly, the Acorn could be booting and I can’t see the display as has defaulted to a screen setting (resolution and/or refresh rate) that my modern(ish) TFT monitor is very unhappy displaying. I’ve tried holding down ‘DELETE’ on boot-up and also the ‘R’ Key ( which should factory reset the settings), without much success.  Ideally, what I need to do is investigate what the A5000 defaults to for display settings (especially after a reset), and try a couple of different monitors, maybe an older CRT monitor if I can track one down. Also, a possibility might be to build a SCART cable and try it on the CRT TV I do have.

Second, the Acorn could be booting and running, but be faulty in a way that the display does not show anything. Theoretically it should flash the Floppy Drive access LED as a kind of ‘BIOS POST code’, however my Acorn does not have the original Floppy Drive. Quite early on, it became obvious the original drive was faulty, so I simply swapped it for a PC drive, which until now worked fine. It is possible the replacement drive is not showing as the first drive (PC FDD are wired differently with regards to the drive select) and consequently the A5000 is not able to flash the LED. It might not be a bad idea to investigate the drive select and see if I can get the existing drive to produce a status code.

Thirdly, all of the above could be rubbish and wishful thinking. In the end, the old battery has leaked on the mainboard and its highly likely that it has damaged part of the board, which is the root cause of all of the boot issues. I will very likely have to remove the mainboard and visually inspect for damage and clean any residue. Once I’ve inspected the board, I’ll need to repair any obvious signs of damage.

Fortunately, there is a very helpful guide on Retro-Kit (http://www.retro-kit.co.uk/page.cfm/content/Restoring-an-A5000/) which explains some of the diagnosis and repair after just this problem, so I will pretty much follow that and see where I get.

I’d better get my finger out. The halfway point of the month rapidly approaches.