HP 4957A Protocol Analyzer - No power, what to check?  - Page 1
Forum section: electronics / testgear

author: EricJRW
author_rank: Newbie
timestamp: May 09, 2019, 08:27:14 pm
content: Hi all. New here.A Internet search on the subject led me here.Does this unit have a fuse? It's not obvious to me. Plug in and switch to ON, and still nothing. Not even a hum.I'm sure it was working last time I used it, probably over 5 years ago. :-)Was cleaning a closet and came across it. Wanted to remember the good old days of debugging RS-232. Anyone remember TNPP (Telocator Network Paging Protocol)?Any help appreciated.Thank you in advance,Eric

author: gslick
author_rank: Frequent Contributor
timestamp: May 09, 2019, 10:52:17 pm
content: I just tried this on my 4957A. It took a little more force than I expected to flip out the top of the fuse cover. The cover pivots out from the top while the bottom end stays attached.

author: EricJRW
author_rank: Newbie
timestamp: May 12, 2019, 03:02:41 am
content: Thank you!Well the fuse is OK.Is there something else I can check?Eric

author: TheSteve
author_rank: Unknown
timestamp: May 12, 2019, 05:27:23 am
content: TNPP is before my time in paging - did you work in the industry?

author: EricJRW
author_rank: Newbie
timestamp: May 12, 2019, 02:23:41 pm
content: Quote from: TheSteve on May 12, 2019, 05:27:23 amYes, I did. Motorola, back when the pager was the communication device everyone had, or wanted, as cell phones where way to expensive. :-)Prior r to the FLEX paging protocol, most links were RS-232 (even the consoles), or lease line. Internet was still in its infancy.When Mot shuttered paging, I moved onto cellular base stations. Now, even that has ended.It's a shame.You said "before my time inpaging." Are you (were you) in it?

author: TheSteve
author_rank: Unknown
timestamp: May 12, 2019, 06:28:56 pm
content: Quote from: EricJRW on May 12, 2019, 02:23:41 pmThe golden age of paging. I worked for the competition - Glenayre.Any luck with your 4957A?

author: EricJRW
author_rank: Newbie
timestamp: May 14, 2019, 02:57:14 pm
content: Quote from: TheSteve on May 12, 2019, 06:28:56 pmWow, that's a name I have not thought of in a long time. I also worked on the C-Net product, a company Mot bought for its direct sync (i.e. no return required) technology. Bet most people don't know that all paging transmitters (in a coverage area) transmitted the same data at the same time.No luck with the protocol analyzer. The fuse was OK. Guess I'll need to look under the hood.All the best, Eric

author: gslick
author_rank: Frequent Contributor
timestamp: May 14, 2019, 07:36:13 pm
content: On my HP 4957A power supply PCB there is an F1 250V 1.6A fuse, and also an R2 250V 5A 130C. Maybe that is a thermal fuse?The power supply is labeled as Yokogawa PS033-0101, with an HP part number of 950-2274

author: TheSteve
author_rank: Unknown
timestamp: May 14, 2019, 07:56:09 pm
content: Quote from: EricJRW on May 14, 2019, 02:57:14 pmYes, simulcast to the rescue. For a while I worked on the transmitter controllers which handled the synchronization of the transmitted signal and provided a 10 MHz reference to the exciter. They were normally GPS locked, although they could also be programmed with a fixed delay.If you do crack open the 4957A do some basic voltage checks. Make sure something simple like the power switch didn't fail.

author: EricJRW
author_rank: Newbie
timestamp: June 07, 2019, 07:46:09 pm
content: Thank you both!Have not had the time to open the case (chassis).Didn't want to be rude and not update.My '91 Mazda B2600i (260,000 miles) has my attention at the moment.Eric

author: CuriousMarc
author_rank: Newbie
timestamp: October 15, 2021, 10:20:06 am
content: Very late answer to this post, but try to change the small electrolytic C7 near the end of the big green 100k power resistor. That’s the cap for the control circuitry startup power. In my unit it was bad and prevented the power supply from starting.Marc

author: apolon34
author_rank: Newbie
timestamp: October 07, 2022, 12:10:52 pm
content: I want to send you a huge thank for this tip.I have the same protocol analyser which I use at work for years and it had the exact same problem, power supply not starting at all and after replacing C7 it is working again !Many thanks!

author: Halcyon
author_rank: Unknown
timestamp: October 08, 2025, 07:01:57 am
content: Quote from: CuriousMarc on October 15, 2021, 10:20:06 amAre we blessed by *the* CuriousMarc?