Pulsar P2 Transistor Replacement

[charger105]

Hi All.
I recently picked up a speculative P2, hoping to get it working. I replaced the QC, and it sprung to life immediately.......the only problem being that the middle horizontal segment is out

According to Piotr, the transistor shown in green here, is possibly the problem:

http://crazywatches.w.interia.pl/photo/ ... _tech.html

Has anyone got any tips on removal, and re-installation of these bad boys ?

Of course it could be the display, or the IC or the PCB, but I'm hoping it's the transistor. I was thinking of bridging the output with an adjacent segment transistor to test the display. This works on a Synchronar. Anyone got any thoughts on this ?

All help appreciated.
Rgds,
Andrew.

[J Thomas]

[retroleds]

Hi All.
I recently picked up a speculative P2, hoping to get it working. I replaced the QC, and it sprung to life immediately.......the only problem being that the middle horizontal segment is out

Have to ask - is it the horizontal segment on all numbers, or just one?
If it is only one number that is missing the segment, it is a connection between the display and the board, since the same transistor is used for the same segment on all numbers.
If only on one number, I have the board contacts all mapped - tell us which one and I can tell you how to count your way over to the one that isn't making contact - you may be able to tab it with a pin and some epoxy without removing it......

The transistor is a basic silver epoxying job; just don't get sloppy. At all.

The situation is very different on a P4, Men's Dress or Sport module.

[bruce wegmann]

I've lost track of how many of these I've done; you just have to remember, you have to replace a segment driver with a segment driver, and a digit driver with a digit driver...you can't mix them [I'm guessing one is NPN and the other PNP...in any event, any replacement must be done with one of "like type", or it just won't work]. Grip the transistor block firmly with a pair of heavy, blunt-nosed tweezers, give it a twist, and it should break free cleanly. The other thing is, if a segment is missing on all three digits, it's a driver fault, if missing on only one, the problem is in the display itself...probably a broken wire bond [and this is not fixable directly...you need to replace the display]. This all works the same for P3 modules too, of course.

[retroleds]

The other thing is, if a segment is missing on all three digits, it's a driver fault, if missing on only one, the problem is in the display itself...probably a broken wire bond [and this is not fixable directly...you need to replace the display]. This all works the same for P3 modules too, of course.

Bruce, I'd agree that if the segment is only missing in one numeral the problem is in the display. But I disagree that if it is missing in all three it is absolutely a driver issue. There are 11 contacts on the back of that display: 7 are for the segments(driver path) and the other 4 are the "commons" for each numeral. The center one at the bottom is just a physical stabilizer dot.

The driver contact for that particular segment is the 3rd one from the top left corner(of the display/board, if viewed from the front). If that center segment is out it in all numerals the contact at 3rd from top left could be bad and it would be the same effect as a bad driver. If the common for a particular numeral is bad, the whole digit is off. I spent a lot of time and effort mapping the P2/P3 display paths and the P4 paths - but it wasn't a waste of time.

[bruce wegmann]

The contact point COULD be bad, sure enough; I have seen this. But, only once in scores of repairs...so, I would have to say, the odds are certainly in favor [better than 95%] of the transistor being bad, rather than the solder joint [it's still the first thing I would try to get things going again].

[charger105]

Thanks Gentlemen.

The segment's out across all 3 digits. I assume it will be the transistor, but it'd be good to make sure of things before ripping it off the board !

I tried applying pressure to the transistor and display with a paddle-pop stick--------no joy. I also hit the joints with a soldering iron-----again no joy.

I haven't got any silver epoxy at the moment. I reckon I might just be able to solder a new one back on.

Rgds,
Andrew.

[charger105]

Well, the soldering is not going to happen....it's too tight in there.
The good news is I removed the old transistor, and taped a new one in place. With a little light pressure, the segment light right up .

Now Im going to have to order some silver epoxy. It's incredibly expensive here........the last time I looked it was close to AU$100. I think I'll order some from the States.

Rgds.

[bruce wegmann]

I have a local source here in San Diego that sells a 14-gram kit for about $25. It's from MGC, the best material made, IMHO. It's item No. MGC-8331-14G. Go to MGChemicals.com , and put 8331 in their product search. Probably best to order directly from them.

[azimuth_pl]

this is probably the 14g kit you have mentioned 29$:
http://cgi.ebay.com/Silver-Epoxy-Kit-14 ... 0211336497
resistance at 0.38ohm

but this one might be the best available, although more expensive 65$:
http://cgi.ebay.com/Conductive-Silver-P ... 0076940657
0.01ohm resistance which is more than perfect.

has anyone tried it?

[charger105]

Mission accomplished .
Thanks for your advice gentlemen.

I siliconed a small piece of cotton onto the top of the transistor, and lowered it into place with tweezers, using the cotton as a sort of "handle" (I'd placed the silver epoxy onto the pads with a needle just prior). I was probably being a bit too careful, but I'd never done this before, and wanted to make sure I didn't smear the epoxy on the PCB.

To answer your question Piotr, I ordered the first item listed in your post (prior to you posting co-incidentally). I can confirm it worked well for this job. It's a nice consistency when mixed, sets rock hard, and once cured, conducts with no discernable resistance.

I looked at the MG product Bruce, but when I followed their purchasing pathway, it directed me to an Australian distributor, who didn't stock it !

Thanks again.
Rgds,
Andrew.

[egomon]

I have one Pulsar p2 and the one segment on every number is out- so it is a transistor problem.
As i don't have any spare pulsars where to get a replacement I was wondering is there any new replacement transistors available what i can use in my p2?

Regards

Egon

[SASM]

Well I could send an old Pulsar module so that you have spare parts with your Mark I+II movements. I´ve done transistor exchanges right on the original module, but it is very tricky. The pads are very small, but it can be done.

Use a foreceps to remove it and your finger tip to hold the transistor on the board again. Then solder it on the board. It works much better than a foreceps, but you usually loose a bit of you nail which smells terrible.

Don´t foget to file your nail later to avoid annoying comments of our wife.