Fluke 45 Q11/Q13

[dorkshoei]

I picked up a Fluke 45 non working.   

The fact that Q11 and Q13 are missing may be a factor

Manual says:

Q10/Q11 TRANSISTOR,SI,PNP,T092 698290
Q11/Q13 TRANSISTOR,SI,NPN,SELECTED IEBO,TO-92  685404

Q10 and Q11 are present and are  MPS6562 25V 1Amp 625mW

Can anyone tell me what Q11/Q13 are?  I'm curious on what attributes "SELECTED IEBO" translate to.

Thanks!

[bdunham7]

Q11 is the complementary MPS 6560 and I believe I_EBO is simply the emitter-base reverse leakage current, although there may be specific conditions attached to that spec.  I don't know the selection criteria.

[dorkshoei]

What's the best cross for MPS6560 in this application (since it's obsolete)? 

[bdunham7]

There's probably lots of crosses if it wasn't a critical application, but since it likely is I would recommend hunting down the original.  Otherwise you need to have a close look at the circuit.  Rochester Electronics has them for a nickel each, but they want to sell you 6000 or so.  Maybe you can get them to sell you 100 and you will then have plenty from which to select a low-leakage one!

[floobydust]

It looks like Q11/Q13 are part of a full-bridge DC-DC converter fed from a pre-regulator. So the selected parts were more likely high hFE ranking I believe, verses E-B leakage.
I would use Zetex E-line parts, but stock is a bit wonky right now. Just look at 1A or higher collector current TO-92 package and over 25V, from your fav disti.

[dorkshoei]

There's probably lots of crosses if it wasn't a critical application, but since it likely is I would recommend hunting down the original.  Otherwise you need to have a close look at the circuit.  Rochester Electronics has them for a nickel each, but they want to sell you 6000 or so.  Maybe you can get them to sell you 100 and you will then have plenty from which to select a low-leakage one!

https://www.ebay.com/itm/254854237601

Always worried about fakes on eBay.      Also hard to know what a "low leakage" one is when I don't know the spec.    Testing 100 and picking the best sounds like a fun way to spend an evening

[dorkshoei]

I would use Zetex E-line parts, but stock is a bit wonky right now. Just look at 1A or higher collector current TO-92 package and over 25V, from your fav disti.

Ok, I guess Zetex is Diodes Inc now.   Thanks!

[bdunham7]

It looks like Q11/Q13 are part of a full-bridge DC-DC converter fed from a pre-regulator. So the selected parts were more likely high hFE ranking I believe, verses E-B leakage.
I would use Zetex E-line parts, but stock is a bit wonky right now. Just look at 1A or higher collector current TO-92 package and over 25V, from your fav disti.

That PSU circuit makes my eyes hurt, but I think you are right.  I see no reason that reverse leakage would be an issue, so perhaps IEBO is I_EB ON.  I had no idea they would use a 'select' part in a power supply--I guess those were the good old days.

[mikerj]

Neat circuit, don't think I've seen a self oscillating full bridge driver like this before.

[dorkshoei]

Neat circuit, don't think I've seen a self oscillating full bridge driver like this before.

Thanks very much for all the advice.

I'm coming from the software side and so I'm very much an electronics beginner compared to you guys. 

So advice in terms of specific part numbers etc is very much appreciated.   

Based on @floobydust comment these seem to be the e-line parts.

[floobydust]

I would replace all four transistors Q10-Q13, to keep symmettry and I think the design criteria is high beta at high current, which the E-line does pretty good.
At 500mA MPS6560 hFE 50-200.
ZTX450 is 90-270.
ZTX649 is 100-300, graph 200.
ZTX690B is about 500-900 which might be too high.

These small TO-92 parts, will heat up fast if there is a fault or overload downstream, on the secondary of transformer T2. So if there is another problem, I would keep an eye for that.
R46 seems to be kind of a fuse 0R50 1/4W and 45 service manual mentions 210mA or 1.05V across R46 typically and maybe about 10VDC output from U11 at R46?