Finding a suitable replacement for transistor from HP Agilent Keysight schematic - Page 1
Forum section: electronics / repair

author: dlucy67
author_rank: Contributor
timestamp: March 28, 2016, 05:04:56 pm
content: I'm digging into a piece of HP gear, a 3466A digital multimeter, and I need to understand how I'd find a suitable replacement for a given transistor. My question is more of a "how to do this" one versus a "which part do I need in this specific case" question.For instance, I've got a TO-92 at Q906 which has less-than-helpful silkscreen printing on it and the parts list in the schematic hasn't helped me so far. For those of you who know HP Agilent Keysight gear well, how should I decode the following line from the parts list into a real, specific transistor? Once I've got that, I know how to find a replacement (based on cross ref or just parameters):Ref HP PN Description Mfr Mfr PNA4Q906 1853-0016 TRANSISTOR PNP SI TO-92 PD=300MW 28480 1853-0016Googling 1853-0016 doesn't give me anything useful and I don't want to just drop a random transistor in there. Where can I take the above info, look it up, and yield a datasheet or at least the critical parameters to then go look for a replacement transistor?

author: w2aew
author_rank: Super Contributor
timestamp: March 28, 2016, 05:35:47 pm
content: Quote from: dlucy67 on March 28, 2016, 05:04:56 pmAccording to the cross reference information located here:http://www.sphere.bc.ca/test/hpparts.html#crossThe 1853-0016 is electrically equivalent to a 2N3638The specific page I found this on is:http://www.sphere.bc.ca/test/hpdata/hp-xref81-1.jpgThis same site has cross reference info for Tektronix part numbers too:http://www.sphere.bc.ca/test/tekequiv.html

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 28, 2016, 08:00:47 pm
content: Quote from: dlucy67 on March 28, 2016, 05:04:56 pmIf I google 1853-0016 the second result says the equivalent is NTE159:http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=1853-0016googling NTE159 shows me a lot of places where I can buy this.But anyway, it is just a generic audio PNP, so I guess almost anything will work.

author: timb
author_rank: Super Contributor
timestamp: March 28, 2016, 09:16:26 pm
content: The other way to do this, when you can't find the part online or through a cross reference is this: Look through the parts list and find another transistor with the same part number. Unless it's a big power transistor, odds are it's used elsewhere on the board (this saves on inventory costs). Locate it on the board and remove it, then use one of those $20 Chinese transistor testers on it. This will tell you if it's a PNP, NPN, what the HFE is and what the base current is.You can then either use a multimeter or scope to measure voltages between the base-collector and collector-emitter of the broken unit. (Or deduce it from the schematic.)With that information you should have enough information to pick a suitable replacement.

author: dlucy67
author_rank: Contributor
timestamp: March 28, 2016, 09:57:40 pm
content: Quote from: w2aew on March 28, 2016, 05:35:47 pmBrilliant! Exactly the answer I was hoping for. Thank you!

author: dlucy67
author_rank: Contributor
timestamp: March 28, 2016, 09:58:51 pm
content: Quote from: PA0PBZ on March 28, 2016, 08:00:47 pmI must have fat-fingered the number as I searched for it. You are exactly right. Thanks!

author: dlucy67
author_rank: Contributor
timestamp: March 28, 2016, 10:00:08 pm
content: Quote from: timb on March 28, 2016, 09:16:26 pmGreat! Thank you!

author: JFJ
author_rank: Regular Contributor
timestamp: March 28, 2016, 10:48:31 pm
content: Quote from: w2aew on March 28, 2016, 05:35:47 pmHewlett Packard specify the same electrically equivalent transistor in theirJune-August 1981 issue of "Bench Briefs"magazine.There are more cross reference tables, and lots of servicing tips, in the other issues of Bench Briefs that can be found here:http://www.hparchive.com/bench_briefs.htm

author: dlucy67
author_rank: Contributor
timestamp: March 28, 2016, 11:08:06 pm
content: Quote from: JFJ on March 28, 2016, 10:48:31 pmFantastic. Thanks!

author: vk6zgo
author_rank: Super Contributor
timestamp: March 29, 2016, 08:21:33 am
content: Quote from: timb on March 28, 2016, 09:16:26 pmAs a comment on this.Sometimes Manufacturers use the same device in a critical & a non-critical application to save on inventory.If you find another one in a non-critical spot,steal it for the original position.You can often then use a generic device in the non-critical position.

author: dlucy67
author_rank: Contributor
timestamp: June 05, 2016, 08:33:21 pm
content: This has helped considerably and I've found a replacement for 1853-016, but the second transistor I'm chasing down is HP part number 1854-071 which, using the above-referenced HP charts, crosses to a CP4071. I can't seem to find a datasheet on the CP4071 (to help me find an equivalent replacement based on the specs).The device itself has some markings, but I can't find an Internet match for simple combinations of those, either.I've used a B&K 530 semiconductor tester, verified the 1853-016 is a PNP and the 1854-071 is NPN. Both devices seem to pass the leakage tests on the B&K 530, but I'm keen to drop a temporary replacement in for the 1854-071 at Q908, just to see if the flickering behavior changes at all.Anyone know what a CP4071 crosses to? Or where I might find a datasheet?Thanks!

author: G0HZU
author_rank: Super Contributor
timestamp: June 05, 2016, 09:03:50 pm
content: Not sure if this is the same part number as it has two zeroes ahead of the 71 but I had several 1854-0071 NPN devices exhibit a 'flickery' failure mode in my old HP8405A vector voltmeter.You can read about my exploits in the link below.See the symptoms in posts #30 and #31 and then on post #32 you can see I found a cross reference to a 2N3391 in my old HP431C manual.http://www.vintage-radio.net/forum/showthread.php?t=102117&page=2QuoteThey are probably Texas Instruments parts and the ones that failed developed a flicker mode that was temperature dependant.I just used BC547B parts to get it working but I would like to find the correct parts at some point. So I'm interested if you find what these parts are!

author: JFJ
author_rank: Regular Contributor
timestamp: June 05, 2016, 10:48:43 pm
content: Quote from: dlucy67 on June 05, 2016, 08:33:21 pm1854-0071 transistors (with the same 4-071 marking as in your picture) are listed on eBay:http://www.ebay.com/itm/391373647073

author: dlucy67
author_rank: Contributor
timestamp: June 06, 2016, 12:35:07 am
content: Quote from: G0HZU on June 05, 2016, 09:03:50 pmVery good pointers, thanks!I found an on-hand transistor with good enough specs, swapped it in there (for the Q908), and the flickering remains. I'll replace the remaining transistors in the LED segment driver, just to see if that solves the problem. If not, we must have different issues.

author: edavid
author_rank: Super Contributor
timestamp: June 06, 2016, 02:16:25 am
content: I believe 1854-0071 = 2N3704

author: dlucy67
author_rank: Contributor
timestamp: June 06, 2016, 03:32:56 am
content: I've replaced all the LED driver related transistors with good equivalents, but I'm still getting getting the flickering and the entire range of units LEDs at lit, although dimly, at the same time.