Keysight 34465A reliability

[mairo]

My 34465A just failed as well - after a quick check it seems the issue is the mains transformer (internal thermal fuse?) as I measure 0VAC on the two connectors coming out of the transformer (as per the service manual). Mains fuse and power cable are OK.

[coromonadalix]

sometimes you can have access to the thermal fuse and short it out  if there is one, if so  you should see some wires on the xformer going innard ?

[voltsandjolts]

My 34465A just failed as well - after a quick check it seems the issue is the mains transformer (internal thermal fuse?) as I measure 0VAC on the two connectors coming out of the transformer (as per the service manual). Mains fuse and power cable are OK.

Beware it might have failed due to excessive current draw by an earlier failure in the electronics.

[mairo]

It will be interesting to know why it failed. It is the transformer, the input is open circuit. The rest of the circuit looks like brand new (have not tested yet with new transformer tho to confirm). It was very rarely used and only as a voltmeter in 1.8-5V applications. It was working as normal when I last used it several months ago, and when I went to switch it ON few days ago, it wasnt.. Always kept in clean lab environment.

I pilled off the isolation film and there were only wires visible, no fuse. It might be on one of the top/bottom sides, will crack open to see some other time.

Judging by the amount of transformers for these models available for sale on eBay, I am guessing is something that fails often.

The OEM part number is  HL00-11044LF, from Bi Technologies, now part of TT Electronics, but seems custom made probably for Keysight, as no info available.

[Kleinstein]

If there is a thermal fuse, this is often relatively deep inside and hardly accessible. It is only a few lucky cases where the link is actually similar to other terminals.

The transformer should be a custom one with extra shield(s) and good isolation between the 2 secondary windings.

[jundar]

I bought a used 34465A on eBay, so I don’t know its full history. When I opened it up for inspection, I was surprised not to see an LM3S chip — instead, it has a TM4C chip installed.
The front panel is gray, the estimated manufacturing year is 2017 (serial MY575090xx), and the PCB revision is 001.
Can I conclude that my unit really does have a TM4C, despite the gray front panel, the 2017 manufacturing year, and REV 001 PCB?
I had assumed—likely incorrectly—that Keysight’s move from the LM3S to the TM4C happened at the same time as the introduction of the dark-front-panel units, roughly around 2020
I can’t shake the feeling that I may have missed something.

[coromonadalix]

does it works fine ?


but  is this the main pcb ?   what do you have for the display pcb

[KungFuJosh]

I bought a used 34465A on eBay, so I don’t know its full history. When I opened it up for inspection, I was surprised not to see an LM3S chip — instead, it has a TM4C chip installed.

I've seen people mentioning newer versions of the grey 34465A units that had a TM4C instead of the LM3S, and allegedly are immune to the self destruct feature of the older units.

If units after 2017 really are immune, that would be good to know.

[jundar]

does it works fine ?
but  is this the main pcb ?   what do you have for the display pcb

It was working fine before I started disassembling it. Hopefully I’ll manage to put it back together properly.

Do you mean this part of the board (photos attached)? Does the chip’s name suggest anything bad?

Also, I noticed a CR2032 battery. What does it power — just the real-time clock? And is it safe to replace if needed?

[KungFuJosh]

Read this thread starting here: https://www.eevblog.com/forum/buysellwanted/fs-many-keysight-34465a-multimeters/msg5809989/#msg5809989

[voltsandjolts]

I bought a used 34465A on eBay, so I don’t know its full history. When I opened it up for inspection, I was surprised not to see an LM3S chip — instead, it has a TM4C chip installed.

I've seen people mentioning newer versions of the grey 34465A units that had a TM4C instead of the LM3S, and allegedly are immune to the self destruct feature of the older units.

If units after 2017 really are immune, that would be good to know.

The LM3S self destruct was the less common self destruct mechanism of these dmm's. More common is front panel SPEAR mcu (as jundar's unit has) or corruption of the nand that holds the program code for it.

[KungFuJosh]

The LM3S self destruct was the less common self destruct mechanism of these dmm's. More common is front panel SPEAR mcu (as jundar's unit has) or corruption of the nand that holds the program code for it.

Weren't they connected? I thought I read somewhere (maybe in that thread) that the presence of the LM3S made the SPEAR failure more likely?

[voltsandjolts]

I'm not aware of that. Keysight made sure there were at least 3 _independent_ ways the dmm would self destruct

[KungFuJosh]

 Keysight for the "win."

[jonpaul]

Change in HV max rating of 2017 units SN MY57 or below.

See https://hpwiki.org/_media/service_notes:34465a-01.pdf

No recall.

No serv wty extend AFIK.

The unit I have was new in 2020, SN MY60xxxxxx

Still in perfect  CAL. Passes all tests.

Jon

Jon

[Hydron]

That service note was withdrawn IIRC, there's a whole thread about it and Dave made at least one video on the topic.