Fluke 45 Q11/Q13 - Page 1
Forum section: electronics / repair

author: dorkshoei
author_rank: Frequent Contributor
timestamp: November 09, 2021, 03:19:52 am
content: I picked up a Fluke 45 non working.The fact that Q11 and Q13 are missing may be a factorManual says:Q10/Q11 TRANSISTOR,SI,PNP,T092 698290Q11/Q13 TRANSISTOR,SI,NPN,SELECTED IEBO,TO-92 685404Q10 and Q11 are present and are MPS6562 25V 1Amp 625mWCan anyone tell me what Q11/Q13 are? I'm curious on what attributes "SELECTED IEBO" translate to.Thanks!

author: bdunham7
author_rank: Super Contributor
timestamp: November 09, 2021, 03:55:41 am
content: Q11 is the complementary MPS 6560 and I believe IEBOis simply the emitter-base reverse leakage current, although there may be specific conditions attached to that spec. I don't know the selection criteria.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: November 09, 2021, 04:59:49 am
content: What's the best cross for MPS6560 in this application (since it's obsolete)?

author: bdunham7
author_rank: Super Contributor
timestamp: November 09, 2021, 05:22:17 am
content: 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!

author: floobydust
author_rank: Super Contributor
timestamp: November 09, 2021, 05:44:57 am
content: 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.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: November 09, 2021, 05:48:08 am
content: Quote from: bdunham7 on November 09, 2021, 05:22:17 amhttps://www.ebay.com/itm/254854237601Always 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

author: dorkshoei
author_rank: Frequent Contributor
timestamp: November 09, 2021, 05:53:18 am
content: Quote from: floobydust on November 09, 2021, 05:44:57 amOk, I guess Zetex is Diodes Inc now. Thanks!

author: bdunham7
author_rank: Super Contributor
timestamp: November 09, 2021, 06:11:21 am
content: Quote from: floobydust on November 09, 2021, 05:44:57 amThat 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 IEBON. I had no idea they would use a 'select' part in a power supply--I guess those were the good old days.

author: mikerj
author_rank: Super Contributor
timestamp: November 09, 2021, 11:02:06 am
content: Neat circuit, don't think I've seen a self oscillating full bridge driver like this before.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: November 09, 2021, 04:04:10 pm
content: Quote from: mikerj on November 09, 2021, 11:02:06 amThanks 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.

author: floobydust
author_rank: Super Contributor
timestamp: November 10, 2021, 06:29:37 pm
content: 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 500mAMPS6560 hFE 50-200.ZTX450is 90-270.ZTX649is 100-300, graph 200.ZTX690Bis 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?