MattisLind
Veteran Member
A friend of mine got an IBM 5110 which was dead and I am trying to help out. It blows fuses. First he told me the transformer was short circuit. When I looked at the PSU I recognised that it was a switcher. And quickly concluded that one of the chopper transistors was a three pole short.
The chopper transistors were TI made in 1978 but marked T484. Probably some IBM marking which no one has the cross for.
I replaced them with nice high voltage high current TO3 transistors The only thing i could get from the original transistors except for the physical appearance was the polarity.
With a 5.6 ohm resistor on the 5V output I fired up the PSU with a 60W lightbulb in series with one of the mains leads. Nothing happened on the bases of the switchers until I got to around 190 VAC input.
At that point the base went high and stayed there. There seems to be very little power consumption since the bulb goes dark after the initial charging of the input capacitor of the PSU. There is a faint click sound heard from some part of the PSU when turning it on, but cannot really get exactly where. I suspect the sound comes from the transformer. If turning on using variac it happens exactly at the same time as the base voltage changes.
Have measured most of the semiconductors and they measure fine. Except for possibly one that look like a transistor but it hard to tell since it has just IBM number on it. Cannot detect any PN junction on it.
Of course I have no schematics for this IBM thingie. Does anyone have a schematic for the IBM 5110 PSU? I think I really need it to understand what is going on.
Tracing it out is an option but then all those square metal canned IBM ICs makes it very difficult...
The chopper transistors were TI made in 1978 but marked T484. Probably some IBM marking which no one has the cross for.
I replaced them with nice high voltage high current TO3 transistors The only thing i could get from the original transistors except for the physical appearance was the polarity.
With a 5.6 ohm resistor on the 5V output I fired up the PSU with a 60W lightbulb in series with one of the mains leads. Nothing happened on the bases of the switchers until I got to around 190 VAC input.
At that point the base went high and stayed there. There seems to be very little power consumption since the bulb goes dark after the initial charging of the input capacitor of the PSU. There is a faint click sound heard from some part of the PSU when turning it on, but cannot really get exactly where. I suspect the sound comes from the transformer. If turning on using variac it happens exactly at the same time as the base voltage changes.
Have measured most of the semiconductors and they measure fine. Except for possibly one that look like a transistor but it hard to tell since it has just IBM number on it. Cannot detect any PN junction on it.
Of course I have no schematics for this IBM thingie. Does anyone have a schematic for the IBM 5110 PSU? I think I really need it to understand what is going on.
Tracing it out is an option but then all those square metal canned IBM ICs makes it very difficult...