tezza
Veteran Member
Re: previous "Help" thread. Thank you Ryan, thank you Nige. I now have a working Osborne 1. You were right, it was a faulty RAM chip.
As with the other two units I've repaired this week, this was a satisfying adventure.
First I removed the case, exposed the CPU board and identified the RAM chips with a view to feeling which ones were hot. The first obstacle was that I couldn't get to all the RAM chips. Even with the board exposed, about a third of the chips were covered by the floppy controller which was stacked over them. What's more, I couldn't remove this without breaking glued clips holding it in place. It was also plugged directly into the board, so it had to be in that position anyway while the computer was on. So...I just hoped that if a RAM chip was faulty, it wasn't one in the bank hidden under this interface.
Ok, so with the mainboard unscrewed and pulled back, I switched the machine on and left it going for about 20 mins. Then I felt the RAM chips I could get to. Hmmm...they ALL seemed a little hot...but some seemed hotter than others? There was no one chip that stood out although a cluster of them did seem to be a little hotter. Maybe one of those, I mused? Although perhaps there was a really hot one in the place I couldn't get to. There was no way I would know.
Then I thought, well diagnosis is one thing, but how am I going to replace a chip that's faulty anyway. I had no 4116s lying around! Or….maybe I did...? I suddenly thought of one of my (Z-80) System 80 computers. I've got one machine I use for parts. Could I get a compatible RAM chip out of that?
I grabbed the System-80 manual, and sure enough...the RAM chips were 4116 ones! Yay! But then...I'd never de-soldered a chip before. How easy was that to do? However, I opened up the "parts" System-80 and, lo and behold, the RAM chips were socketed!!! Someone was smiling on me!!
I removed a RAM chip from the System 80 socket. These RAM chips had two others piggybacked on top of them as part of a homebrew memory expansion but some clipping took care of those. So…now I had a replacement 4116 ready...if indeed this was the problem.
Taking the chip, I piggybacked it onto one of the chips in the "hotter" grouping, by just pressing it over the top and letting the legs hold it there by friction. Then switched on the machine. Same symptom. I tried the same procedure with another chip next door. No joy. I tried it with a third chip. Suddenly the Osborne Boot-up screen appeared!
After I stopped dancing around the room, it was all hands to the snippers, soldering iron and de-wick to remove the faulty chip. This was actually quite easy..partly because I had some experience now and partly because the Osborne board was much bigger than the SX-64 board that I'd worked on yesterday. It didn't take me long. I had a socket left over from the lot Druid6900 had sent me for the SX-64, so I soldered this in to the board and then plugged the 4116 in. You can see this in the attached image.
I then re-assembled the case and switched it on. There was that beautiful splash screen again, asking me to insert the boot disk. I had obtained the machine with the original Osborne disks and these worked! You can see the full system in the second image.
At the time of writing the Osborne has been on for 7 hours solid. It's going fine, although there was one point where I was swapping a disk and suddenly the machine went crazy..the screen garbaged and drives started spinning. I turned it off and turn it on and it hasn't done it since. Hopefully just a stray power surge?
So...I'm very happy. I've fixed three of my computers in the last 4 days, thanks to suggestions and help from people here. Nowithstanding the faulty RS-432 in the BBC, the only remaining "crook" computer is the Vic-20. A member of this forum is going to send me a motherboard for this, so that should be going in due time too.
It's been fun and I've picked up some skills in the process.
As with the other two units I've repaired this week, this was a satisfying adventure.
First I removed the case, exposed the CPU board and identified the RAM chips with a view to feeling which ones were hot. The first obstacle was that I couldn't get to all the RAM chips. Even with the board exposed, about a third of the chips were covered by the floppy controller which was stacked over them. What's more, I couldn't remove this without breaking glued clips holding it in place. It was also plugged directly into the board, so it had to be in that position anyway while the computer was on. So...I just hoped that if a RAM chip was faulty, it wasn't one in the bank hidden under this interface.
Ok, so with the mainboard unscrewed and pulled back, I switched the machine on and left it going for about 20 mins. Then I felt the RAM chips I could get to. Hmmm...they ALL seemed a little hot...but some seemed hotter than others? There was no one chip that stood out although a cluster of them did seem to be a little hotter. Maybe one of those, I mused? Although perhaps there was a really hot one in the place I couldn't get to. There was no way I would know.
Then I thought, well diagnosis is one thing, but how am I going to replace a chip that's faulty anyway. I had no 4116s lying around! Or….maybe I did...? I suddenly thought of one of my (Z-80) System 80 computers. I've got one machine I use for parts. Could I get a compatible RAM chip out of that?
I grabbed the System-80 manual, and sure enough...the RAM chips were 4116 ones! Yay! But then...I'd never de-soldered a chip before. How easy was that to do? However, I opened up the "parts" System-80 and, lo and behold, the RAM chips were socketed!!! Someone was smiling on me!!
I removed a RAM chip from the System 80 socket. These RAM chips had two others piggybacked on top of them as part of a homebrew memory expansion but some clipping took care of those. So…now I had a replacement 4116 ready...if indeed this was the problem.
Taking the chip, I piggybacked it onto one of the chips in the "hotter" grouping, by just pressing it over the top and letting the legs hold it there by friction. Then switched on the machine. Same symptom. I tried the same procedure with another chip next door. No joy. I tried it with a third chip. Suddenly the Osborne Boot-up screen appeared!
After I stopped dancing around the room, it was all hands to the snippers, soldering iron and de-wick to remove the faulty chip. This was actually quite easy..partly because I had some experience now and partly because the Osborne board was much bigger than the SX-64 board that I'd worked on yesterday. It didn't take me long. I had a socket left over from the lot Druid6900 had sent me for the SX-64, so I soldered this in to the board and then plugged the 4116 in. You can see this in the attached image.
I then re-assembled the case and switched it on. There was that beautiful splash screen again, asking me to insert the boot disk. I had obtained the machine with the original Osborne disks and these worked! You can see the full system in the second image.
At the time of writing the Osborne has been on for 7 hours solid. It's going fine, although there was one point where I was swapping a disk and suddenly the machine went crazy..the screen garbaged and drives started spinning. I turned it off and turn it on and it hasn't done it since. Hopefully just a stray power surge?
So...I'm very happy. I've fixed three of my computers in the last 4 days, thanks to suggestions and help from people here. Nowithstanding the faulty RS-432 in the BBC, the only remaining "crook" computer is the Vic-20. A member of this forum is going to send me a motherboard for this, so that should be going in due time too.
It's been fun and I've picked up some skills in the process.
