Well I have been reading all sorts of good stuff from everyone but I'm just not upto helping anyone with so many cluey members so I though I would write a short missive on what I am upto so I can get out of just "lurking".
Well in my side of the world it's hot!! 35-42 degree celcius temps for days so not much gets done and I finally have a chance to sit down and get a cpu board running that I have been trying to get going for many months.
The cpu board is 1982 vintage and I was given it in "unknown condition" so I pulled out an 11 volt 1amp plugpak and wired it to the 8 volt rail of a small 4 slot motherboard I have. I measured the 5 volt regulator on pin 24 of the spare empty socket for boot roms and it was near zero volts.
The next step was get the magnifier out and have a look around the CPU board and I didn't find anything like a track s/c so I proceeded to pull out the regulator (78H05) and refit it with a known working reg. Powered up the CPU board and still no 5 volts.
I then started to pull the chips out 2 and 3 at a time and power the board, still nothing. By the time I finished I had all the chips out. This obviously left the board itself or the "odds and ends" circuitry as the cause of the problem.
I put the magnifier back on the board and found a ceramic cap that looked suspect, pulled it out and still no 5 volt supply.....mmmmmm
Anyway I was thinking for a short time and the regulator current must be going somewhere, then I ran my finger over part of the Power-On-Clear circuitry and low and behold I found this tantalum capacitor that was very warm.
Removed tantalum capacitor and voilia!! ....5 volts supply rail again.
Moral to a 1 hour story.....I hate tantalum capaciors...it's replaced by a 1 uF 63 volt electrolytic.
Well at this stage I had a desktop covered in IC's and my CPU board so I though I might use this point to my advantage. I dragged out a device I bought when I was more affluent and it's called an ALL-01 or specifically it plugs into an IBM 8088 or 286 and can program eproms, 8050 somethings and has the ability to signature test 74 and CMOS series IC's. If you can find one they can be a godsend for making custom system eproms and finding faults.
At this stage my yourgest son came into my study so I was selecting the ic's and I showed him how to identify a particular IC, program the tester and give the IC a couple of tests to see if it was OK. Once he understood what I was doing and why I was doing it he had a marvelous experience helping. Anyway we chewed our way through all the CPU board's ICs and found a 74LS139 that failed but all the other 40 something IC's were OK. Moral to this episode, check everything!!....that could have been a hair tearing episode trying to find that faulty 74LS139 with the board powered up and not operating properly.
Anyway I restuffed the board, tested it's boot eprom was OK and it's waiting to be powered up. To be honest one thing worries me is just how reliable the 30 year old sockets are going to be but that...I will leave to another day.
How does everyone do this stuff ?? Any thoughts on getting S100 boards running ??
Erg
Well in my side of the world it's hot!! 35-42 degree celcius temps for days so not much gets done and I finally have a chance to sit down and get a cpu board running that I have been trying to get going for many months.
The cpu board is 1982 vintage and I was given it in "unknown condition" so I pulled out an 11 volt 1amp plugpak and wired it to the 8 volt rail of a small 4 slot motherboard I have. I measured the 5 volt regulator on pin 24 of the spare empty socket for boot roms and it was near zero volts.
The next step was get the magnifier out and have a look around the CPU board and I didn't find anything like a track s/c so I proceeded to pull out the regulator (78H05) and refit it with a known working reg. Powered up the CPU board and still no 5 volts.
I then started to pull the chips out 2 and 3 at a time and power the board, still nothing. By the time I finished I had all the chips out. This obviously left the board itself or the "odds and ends" circuitry as the cause of the problem.
I put the magnifier back on the board and found a ceramic cap that looked suspect, pulled it out and still no 5 volt supply.....mmmmmm
Anyway I was thinking for a short time and the regulator current must be going somewhere, then I ran my finger over part of the Power-On-Clear circuitry and low and behold I found this tantalum capacitor that was very warm.
Removed tantalum capacitor and voilia!! ....5 volts supply rail again.
Moral to a 1 hour story.....I hate tantalum capaciors...it's replaced by a 1 uF 63 volt electrolytic.
Well at this stage I had a desktop covered in IC's and my CPU board so I though I might use this point to my advantage. I dragged out a device I bought when I was more affluent and it's called an ALL-01 or specifically it plugs into an IBM 8088 or 286 and can program eproms, 8050 somethings and has the ability to signature test 74 and CMOS series IC's. If you can find one they can be a godsend for making custom system eproms and finding faults.
At this stage my yourgest son came into my study so I was selecting the ic's and I showed him how to identify a particular IC, program the tester and give the IC a couple of tests to see if it was OK. Once he understood what I was doing and why I was doing it he had a marvelous experience helping. Anyway we chewed our way through all the CPU board's ICs and found a 74LS139 that failed but all the other 40 something IC's were OK. Moral to this episode, check everything!!....that could have been a hair tearing episode trying to find that faulty 74LS139 with the board powered up and not operating properly.
Anyway I restuffed the board, tested it's boot eprom was OK and it's waiting to be powered up. To be honest one thing worries me is just how reliable the 30 year old sockets are going to be but that...I will leave to another day.
How does everyone do this stuff ?? Any thoughts on getting S100 boards running ??
Erg
