I'm sorry, but I need to come with som critism. It really hurts seeing you brute force it open. You should have done what you said, and read the manual (or search online). It was just that red platic piece that mad it difficult to open. It is very easy to take out, but its a bit counter intuitive, so anybody that are planning to open a 34401, please read how to remove this plastic piece. The same piece is also in the back of the instrument,k if you plan to take the PCB out.
Lol that pretty much most engineer and techs if it isn't test gear, it unfinish projects waiting for parts and etc. I rarely see a completely clean bench.
Since there's a Part II I'm guessing you end up repairing it. Ian Johnson has repaired several of these on his channel. I was grimacing when you were removing the front panel as I knew from his videos that red latch had to be manipulated to get it off, ouch! Hope you are successful!
It's definitely something related to the f segment output drive of the vfd controller chip as the tube is multiplexed and every f segment flickers all together.
Seeing this thing taken apart makes one realize just how much HP has gone down. Thanks Carly! Flickering acts like intermittent open circuit. Since its so hard to fix, and you have little to lose, bake it in the oven at 350 F for an hour.
To me the symptoms suggest that the VFD is ok and that the Driver IC has failed internally. Visually, on a scope the drive signals will appear similar because the failure relates to the multiplexing, in that one segment is not being "Gated" correctly. From memory this is all done within the micro controller on the front panel board, which has internal PROM...may be difficult to source. I seem to remember that there is a dump of the PROM code on XDevs if you can find a uC.
Dude, with all those little elements inside the VFD… I kept waiting for the percussion test ! Isolate mechanically, tap the boards, chassis… give stuff a thump here and there. Maybe a weld in the VFD ?
I'm sorry, but I need to come with som critism. It really hurts seeing you brute force it open. You should have done what you said, and read the manual (or search online). It was just that red platic piece that mad it difficult to open. It is very easy to take out, but its a bit counter intuitive, so anybody that are planning to open a 34401, please read how to remove this plastic piece. The same piece is also in the back of the instrument,k if you plan to take the PCB out.
24 ft² of bench, only 1ft² usable on demand. I guess I'm not the only one :D
we need a support group
Hah! Me too. I'm a stacker from way back when.
Lol that pretty much most engineer and techs if it isn't test gear, it unfinish projects waiting for parts and etc. I rarely see a completely clean bench.
Since there's a Part II I'm guessing you end up repairing it. Ian Johnson has repaired several of these on his channel. I was grimacing when you were removing the front panel as I knew from his videos that red latch had to be manipulated to get it off, ouch! Hope you are successful!
This is not the way to take it apart! read the manual! I did & it came apart fairly easily
what's a manual? Yes I should have done that. once apart I figured it out
It's definitely something related to the f segment output drive of the vfd controller chip as the tube is multiplexed and every f segment flickers all together.
If the vacuum went bad it would just go blank alltogether. Since it's so sharp and bright, vacuum is good.
Seeing this thing taken apart makes one realize just how much HP has gone down. Thanks Carly! Flickering acts like intermittent open circuit. Since its so hard to fix, and you have little to lose, bake it in the oven at 350 F for an hour.
TH-cam runs Maybelline makeup commercials for IMSAI Guy videos. There is still hope that AI won't take over the world.
maybe I need my nails done, I smell a sponsorship 😎
@@IMSAIGuy IMS Associates Inc - Optics, Microqaves & Nails.................
To me the symptoms suggest that the VFD is ok and that the Driver IC has failed internally. Visually, on a scope the drive signals will appear similar because the failure relates to the multiplexing, in that one segment is not being "Gated" correctly. From memory this is all done within the micro controller on the front panel board, which has internal PROM...may be difficult to source. I seem to remember that there is a dump of the PROM code on XDevs if you can find a uC.
I hate it when my stuff breaks,... my condolence.
It will come back, just like ---
its the IDC cable
I have the LCD version of that meter... I do like the VFD display a lot more though.
what is the part number? HP had a 5.5digit meter that was lcd but I don't know of a 6.5digit one
@@IMSAIGuy 3478A (5.5 digit). All those 4-wire/Kelvin meters look the same.. ;)
That's very lucky! It will probably die soon just hope it is years before it fails.
why not probing that specific pin responsible for that segment and comparing with others? Ofc. with the knowledge of multiplexing.
I did look at all the drive levels. they seemed fine
@@IMSAIGuy ok, thx for the feedback.
I don't think it is the VFD.
that was my guess also, but if the problem is the driver chip then will be too hard to replace and I'm better off getting a new meter
@@IMSAIGuy Bake it at 350 F for an hour or two.....nothing to lose
you needed to press down on the red clips watch ianscott johnsons repair video it may help you th-cam.com/video/zfRiGyrfaoY/w-d-xo.html
Dude, with all those little elements inside the VFD… I kept waiting for the percussion test ! Isolate mechanically, tap the boards, chassis… give stuff a thump here and there. Maybe a weld in the VFD ?
I thumped it a lot, no change