Agilent 34410A Fanless Mod - Page 1
Forum section: electronics / projects

author: Mickle T.
author_rank: Frequent Contributor
timestamp: April 19, 2025, 07:29:39 am
content: Since I had children, I have stopped tolerating noisy measuring equipment, especially when it works at night. The only exception is a stack of 8.5-digit DMMs, but you can forgive them a lotAs everyone knows, the Agilent 34410A has a relatively noisy fan with a shrill high-frequency squeal. I have been fed up with this for a long time, so I was ready to press the button to order the SUNON HA30101V3, but I was stopped by an idea suggested by the participants of the "Ru Cal Club": "what if we just turn off this fan?".Having conjured with a thermal imager, I found out that the multimeter has a powerful local heat source in the form of two stabilizers U802 (LM337) U803 (LM317) with a huge voltage drop on them (over 10 V). These stabilizers, located next to the front-rear switch, heat up to 84°C when the fan is turned off at an external temperature of 28-30°C.Having removed the stabilizers from the PCB and moved them to the heatsink located outside the case, it was possible to reduce the average temperature inside the multimeter case to normal and reduce the temperature gradient near the input circuits.As a result, the device became completely silent. The temperature of the outer wall of the AG34410A case is only 3°C higher than the case temperature of the 6.5-digit Credix DM500 located nearby, and the heating of the stabilizers decreased by ~30°C.The multimeter readings after modification when measuring 10 V from the programmable DC-Cal Mini LTZ calibrator did not change even by 1 ppm. The input leakage current increased from 0.8 to 8 pA, which is quite acceptable.

author: guenthert
author_rank: Frequent Contributor
timestamp: April 19, 2025, 08:14:07 am
content: And I would have thought either the faster MCU (allowing much faster readings then the 34401A) or the built-in current shunt were the reasons for the fan. Wonder why Agilent chose such a high voltage drop over the regulators. Did they just happen to have a surplus of a transfomer used for a previous model? In Agilent's defense, the instrument does settle into a stable state very quickly with virtually no wam-up time and can hence be used like a hand-held DMM: turn on, when needed. Perhaps a sleep-mode when idle is needed.I quite like the mod, reminds me of the externally placed power transistor in the 3456A. Not quite ready to commit on it though. The 34410A is the instrument I spent the most on while it is woefully underutilized and I'm contemplating selling it (but I do that for a few years already -- the built-in statistics functionisnice).

author: the Chris
author_rank: Regular Contributor
timestamp: April 19, 2025, 08:52:23 am
content: Thanks for investigating. I replaced the original fan by a MF30101V21000UA99, but that was still too loud for my liking. After adding a 100Ohms resistor, as suggested by HighVoltage, noise is fine. Looks like I need to take a look at heat dissipation, did not notice any strong sources when working on it.

author: Sorama
author_rank: Frequent Contributor
timestamp: April 19, 2025, 08:58:20 am
content: Unless you have determined the emissivity of those measured materials and set the camera accordingly, your temperatures are not trustworthy and way off.

author: Mickle T.
author_rank: Frequent Contributor
timestamp: April 19, 2025, 09:16:36 am
content: I thought it was clear without a reminder that the IR camera in this case is not a measuring instrumentNevertheless, the settings of the IR camera emissivity coefficient were verified with a contact thermometer (the difference in point estimates of 1-3°C was quite acceptable for me).

author: Sorama
author_rank: Frequent Contributor
timestamp: April 19, 2025, 09:35:05 am
content: Can’t agree.You’re taking it images of objects with very different emissivity while you can only set 1 emissivity factor in the camera.Not to mention the impact of reflection.So your pictures are simply no representation of real dissipation and therefore should not be shown.

author: Mickle T.
author_rank: Frequent Contributor
timestamp: April 19, 2025, 09:42:17 am
content: Quote from: Sorama on April 19, 2025, 09:35:05 amOK. All IR images have been removed.

author: guenthert
author_rank: Frequent Contributor
timestamp: April 19, 2025, 01:46:45 pm
content: Quote from: Sorama on April 19, 2025, 09:35:05 amWhat? This is a thread about modification of a DMM, not about thermometry. Close your eyes if you're easily offended.Remarking that the images might not reflect thermal reality is fine, demanding that those be removed is most certainly not.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 19, 2025, 01:54:00 pm
content: The hot regulators are linked to the input side / COM terminal. So the isolation on these regulators can be critical.Having strong localized heat sources like the regulators inside the meter can be an issue and cause thermal instability.The fan has 2 effects: it cools the parts, especially strong local sources. The 2nd point is that with a fan stabilization of the temperature is faster. Usually something like 1/2 hour with a fan and 2 hours without a fan. So removing the fan will cause more time for stabilization after turn on.