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A1 XE G4 933Mhz CPU module recovery

Following the successful Scunthorpe show in April2005 I was looking forward to a good show at BB3 that summer. Only trouble was my A1 had other ideas and promptly stopped working about 1 month before BB3.

Swisso at a local show
Swisso at a local show

To say the A1 just stopped working is wrong, it started playing up first. It would boot to OS4 to begin with and I could only just get the u-boot screen sometimes. I changed the battery on the motherboard first, but it made no difference. I checked the cards and the memory by substitution, fortunately I had built my wife's PC using the same graphics and sound cards, and the memory worked in the PC. All that was left to check was the CPU module and the motherboard and power supply. After swapping the PSU from another tower and retesting I found the A1 would not boot at all. It was time for a complete strip down, after which I found the damage to the CPU module capacitors near the mounting holes. I had changed the small Thermaltake cooling fan very soon after first receiving my A1 because I had wanted to take advantage of the overclocking possibilities; against advice I know and it probably precipitated the demise of the CPU. The new cooler was a large beast which had to have a support bracket to alleviate the strain on the module.

The damaged CPU module
Notice the damaged components - raised from the board

What was done was done as they say and I was left looking for a replacement CPU module and having to take my A1200 tower to BB3 instead whilst I attempted to replace or repair my CPU module. My initial enquiries met with some derisory remarks but in general most people were sympathetic, however I had not foreseen the lack of replacement parts and the discontinuation of the Mai Logic link. Various posts and e-mails on Amigaworld.net gave me some contacts and introduced me to some very helpful people, without whom I would never have found a solution to my dilemma. You know who you are and I appreciate all your help and advice.

One contact suggested I try to find a replacement CPU from Freescale, unfortunately the range had been discontinued and there was no stock left. There was some stock at a couple of other suppliers but they were only interested in selling off their complete stock in units of 36. I looked again at Freescale and checked the CPU specs, finding there were many more similar CPU's amongst which was the G4 7457.

The specs on this claimed it was a direct pin for pin replacement for the 7455 with the added bonus that it was still in production, with various choices from 933Mhz to 1.3Ghz. The specs married and the core voltage was just enough to be used on the A1. My contact had also suggested that I should ask Freescale for a sample. I had not used this method of obtaining goods since I was at school where we would regularly apply to Cadbury,s for information for our school projects and would receive an info pack and some samples. I had forgotten people still did that.

I registered on their website with my business name (I am a self-employed auto-electrician) and sent a request for a sample CPU 7457 1.3GHz. My reason for the request was to monitor the cooling properties of the CPU in an A1. All credit to Freescale, they contacted me within 24hrs with a positive response to my enquiry and said they would ship the sample.

So I waited and after a couple of weeks a package arrived with not 1 but 4 sample CPU's! I was astonished, incredulous and astounded that I had obtained replacements so easily. Freescale even paid the shipping costs.

My next task was to find a repair facility, however I did not want to tread on other peoples shoes and contacted several people about my success obtaining the CPU's. I wanted to make sure that there were no objections to my trying an independent repair although I made it plain that I wanted to work within the community to obtain a repair path, not necessarily an upgrade path. I tried the French amiga repair center, and even registered on their website but I received no answer. Once again the right connections led me to Max Tretene at 3soft, who was willing to try a repair as he had a connection with a company who may be able to carry out the work. My searches for a local repair shop had been unsuccessful even though we have many electronics companies nearby, Siemens/Plessey being the largest and the most unhelpful. I was happy to sacrifice my module if a repair path became available so I duly sent over the module along with 1 CPU. The first repair to the module was to the capacitors and it was retested to check the existing CPU, sure enough it was duff. The next stage saw the replacement CPU rework and unfortunately the first attempt failed. I sent over 2 more CPUs and asked Max to try again. Success!

The fixed CPU module
The fixed CPU module - note the numbering of 7457

Bear in mind that Max had a number of other projects on his hands at the time and this must have been quite a distraction for him, he came through with the goods earlier this February. I think the elation I felt was like Christmas 1983 when I first opened my Vic20. WOW it worked, Max had found at least 2 speed settings for it on the dip switches and was trying to find more, but it worked and the temperature was nice and low, 30 degrees, fantastic!

Signs of life
Uboot showing the G4 7457 CPU module
Uboot showing the G4 7457 CPU module
Scout running on OS4 also acknowledging the presence of the G4 7457 module
Scout running on OS4 also acknowledging the presence of the G4 7457 module (click the image for a larger view)

I couldn't wait any longer, I had been without my A1 for 18months, I sent Max the remaining CPU to do as he wished with, and received my module back.

I made sure the battery was good on the motherboard and checked all the connections again and the settings Core voltage had to be 1.3V This was the maximum and I was not going to blow this baby up. The dip switches had been set by Max and I didn't alter them to begin with. I had also purchased a smaller cooling fan and carefully mounted it to the CPU module avoiding any contact with the capacitors. Everything was set for switch on .........nothing! I knew the module was ok so I reduced the CPU speed down to 200mhz and tried again.........this time it fired and came to life and I had to remember how to get to my OS4 set-up and U-boot again. Having backed up my software a long time ago I decided to install OS4 final from scratch, once done I switched the dip switches until I had 1.266Ghz and checked the on board temperature at the CPU.... 30 degrees and steady.

The CPU fitted to the motherboard - an A1 XE
The CPU fitted to the motherboard - an A1 XE

Thanks

I would like to thank all who helped me during my Amigaless months and a special thanks to Max and his team for their hard work and perseverance in the face of disappointment and uncertainty. The costs involved were shared by everybody including Freescale, without whose generosity we would not have been so keen to keep trying the repair. The benefit is quite plainly a repair path that works and has been shown to work, notwithstanding the bonus of a good supply of CPU's and an upgrade path for those who wish to persue the speed angle further.

Good luck to all.

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Raoul "Swisso" Penel Bournemouth, England 10/04/2007 Article edited and published: 16th October 2007
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