HP 3458A temperatures - Page 1
Forum section: electronics / general

author: wolfy007
author_rank: Frequent Contributor
timestamp: December 07, 2020, 01:17:26 pm
content: Just got an old HP 3458A going with option 002, had a faulty A6 outguard power board. In any case its up and running and as I just got myself a thermal imager, I thought after it warms up and do a quick check of the meter for voltage readings and resistance, I would take a look at internal temps.It did have a blown IEC input filter at some stage that wasnt properly cleaned up when it was replaced, which I have done, and the A6 board needed a little attention. Other than that it looked good, though I havent backed up and replaced the Dallas chips yet.Most temps where below 50celcius, a couple at mid 50celcius but one reached above 60celcius (specifically the U504 (LM6321N) on A2 board). Above 60 odd degrees celcius seems a touch high, is this normal?I did use some paper to allow normal air flow as if the cover were on, but that chip still seemed a little high. Room temperature was about 24celcius.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 07, 2020, 03:53:22 pm
content: Some of the chips (fast OPs and comparators) run relatively hot. They take quite some current from some +-15 V and thus get hot.The more critical ones are the Elantec comparators, as they are obsolete and no easy direct replacement.

author: enut11
author_rank: Super Contributor
timestamp: December 09, 2020, 07:30:00 pm
content: Hi @wolfy007Great thermal pix. I usually use my un-calibrated index finger to gauge temperature!What thermal device did you use and how did you capture the pictures?enut11

author: wolfy007
author_rank: Frequent Contributor
timestamp: December 10, 2020, 02:25:22 pm
content: Quote from: enut11 on December 09, 2020, 07:30:00 pmFinally decided to graduate from finger to imager, got myself a UTi260B. Have been eyeballing a themal imager for a year and a half now, finally bit the bullet, price was right for what I got I think.It has a USB port and microSD card, I have been pulling the images off via USB.

author: wolfy007
author_rank: Frequent Contributor
timestamp: December 22, 2020, 08:58:42 am
content: I have two fans available in restoring this 3458A, which fan would you choose and why?

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: December 22, 2020, 10:20:23 am
content: Have you checked function "TEMP?" on your 3458A - my unit reads out 38.0°C with Ta = 25.5°C (Lab RT) using a clean FAN filter - The original part number is ebm-papst 612L (12V DC) (attached datasheet)Keysight Part: 03458-68501I would select 12V model with same CFM - same power dissipation and audio noise level (dBA) & Ball bearings.Then I would check function TEMP? and verify if this value is close to the expected value of 38°C with Lab RT Ta = 25.5°CThe proof of the pudding is in the eating ...

author: wolfy007
author_rank: Frequent Contributor
timestamp: December 22, 2020, 10:50:17 am
content: Quote from: ScoobyDoo on December 22, 2020, 10:20:23 amThanks for the reply. I did see the data sheet you have posted and it is one of the reasons I was looking at possibly using the Noctua with a speed limiter (resistor) that comes with it to get similar/same CFM at lower speed. The Noctua isnt ball bearing based but as someone who has used their fans in PC's for many many years, some of which where on 24/7 for 7years without fail, I figured they had a pretty good durability yet are very quiet also. I thought it might make a nice mod.Testing is a good idea, and I will definitely do this if I try these, was checking if someone may have tried these fans as substitutes and found them functional or let me know its a bad idea before I waste my time I suppose. Or has a better idea.RegardsNikPS: the old fan is noticeably noisier than my other two 3548A, so I figured I would replace it also along with any other parts deemed end of life such as electro's and IEC filters etc

author: MiDi
author_rank: Frequent Contributor
timestamp: December 23, 2020, 03:04:53 pm
content: 3458A powers fan with 15V, but if you want to use a series resistor anyway, that would not be a problem for 12V fans.Personally I would not use unspecced mtbf fans, if the unit operates unattended.Maybe3458A Workloggives valueable information - on top of xDevs articles.

author: wolfy007
author_rank: Frequent Contributor
timestamp: December 24, 2020, 08:39:47 am
content: Quote from: MiDi on December 23, 2020, 03:04:53 pmThanks for the reply and link, I have also seen the xdevs page regarding the 3458A.The Noctua claims the A6x25 FLX has a MTTF >150000hours (self-stabilising oil-pressure bearing), just looked up the NMB fan specification sheet which claims 64000hours (ball bearing).Im tempted to use the Noctua with a resistor, unless someone has a reason not to.