segment driver transistors

[clockace]

i have added 4 photos of my repair on a mkI/II pcb. the upper left transistor on the pcb was bad. this made the upper right segment of all digits across the display not work. i carefully unsoldered a good one from a scrapper pcb and replaced the bad one. i soldered it down rather than use silver epoxy. the way i did this is put a tiny spot of solder on the 3 pads and then place the good transistor on the 3 pads. starting with the larger of the 3 pads on the transistor, i carefully heated it while gently pressing down with a piece of pegwood. in a few seconds the solder melted. then i went to the other 2 pads one at a time and repeated the process. it is probably not completely soldered down to the pcb pads, but the connection is there and good. this is no doubt the most intricate soldered job i have ever done. maybe it can't even be done, but nobody told me that. peter

[azimuth_pl]

good to know, my Barry lots are still waiting in the project pipeline.
how do you check if a transistor is good or not? I don't have any complicated instruments.

[clockace]

i don't either. the only piece of sophisticated equipment i have is a beatup voltmeter. i have a schematic of the mkI/II's and it shows which segment is driven by which transistor. if a segment is out, i assume it must be a transistor. they are all the same so it doesn't matter which one you use as a replacement, but you do need to know which one is bad. the first thing i do with a bad module is replace the cells. if it still doesn't lite up i replace the qc. from there, if there is no corrosion under the sc that damages things, you should be good to go. put it under a lamp and see if the cells charge up. if not, i then change the sc. you can check the sc if you have a voltmeter. under an incandescent lamp of 75-100watts the sc should be putting out 3+ volts. if not it is bad also. hope this helps. peter

[azimuth_pl]

thanks Peter, when I'm ready for my few dozen Synchronar modules I'll know where to ask :)
so far, to many Pulsars, Optels, Jump hours, Hamilton Electrics, Tuning Forks of all sort.... I've lost track and need to focus on one thing at a time. The mood is usually the issue as I swap projects when I'm bored or anoyed with one or the other.
Currently I'm restoring some 30 Pulsars that I have retrieved from all possible drawers. They have been sitting there for a few years.... but it's pure hell, mayhem... never again.
Synchronars are close, a few months that is ;)

[charger105]

Hi Peter/Piotr.

Just for completeness, I should add that the segment driver transistors are all the same (PNP), but the digit driver transistors are the opposite (NPN). Hence, don't try to interchange these !

At least that's what is outlined in the MkI/II circuit schematic I have.
Rgds,
Andrew.

[azimuth_pl]

thanks, that would make sense as it's the same format in the P2 and P3 :)

[clockace]

yuuupppp, that's why the schematic is so important. peter

[redcar66]