Author Topic: HP 34401a DMM with leaking segments  (Read 77999 times)

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Offline mmx01

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Re: HP 34401a DMM with leaking segments
« Reply #200 on: February 28, 2024, 05:53:35 pm »
I have wired red led with flag byte_not_read. With oled configured it does turn on from time to time but this is not aligning with oled defects.

With led off defects still appear. However without oled, red led does not come on.

Agreed serial issues appear independent from oled issues in a sense for oled there's more a bit flip issue than half byte lost with serial.

I put some time captures in SW, for message to message the period measured from first interrupt until EOF is avg. 116800us = 8.5Hz. Since I push the buffer out to display on EOF (all bytes in the buffer), I would expect it to be okay. i2c could handle up to 40fps, so there's room there. i2c is set to 400kHz.

https://youtu.be/vYpie1gxGXQ


For ringing mitigation I put short cables and series resistors but little to no change. Will try with STM32 tomorrow and if not getting anywhere will get a cheapo logic analyzer.

18:00:57.821 -> 204F5554505554204F 64620000.
18:00:57.821 -> 7474757972737674757476757500.116407.
18:00:57.821 -> 204F5554505554204F464620000.
18:00:57.821 -> 7574767579747574747474747600.116918.
18:00:57.821 -> 204F5554505554204F464620000.
18:00:57.821 -> 7474747574787576747675737700.116913.
18:00:57.821 -> 204F5554505554204F464620000.
18:00:57.821 -> 7677737673757574737676747700.116896.
18:00:57.821 -> 204F5554505554204F464620000.
 

Offline mmx01

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Re: HP 34401a DMM with leaking segments
« Reply #201 on: February 29, 2024, 04:03:38 pm »
So with STM32F4 board everything works fine with the same i2c oled... no defects. Processing time for each byte has not changed between ESP32 and STM32 however, frame processing time is 26% faster with STM32.

Indeed ESP32 GPIOs are not running at 240MHz like the cores do, but still the APB bus runs on 80MHz. I had not expected issues with the ESP32 performance for this not very complex decoding task yet empirically it proves to be the case.

Now I can move on to mapping other codes for different display features.

15:57:13.908 -> 204F5554505554204F464620000.
15:57:13.908 -> 7474747475747474747574747400.86855.
15:57:13.908 -> 204F5554505554204F464620000.
15:57:13.908 -> 7474757474757575757474747400.86555.
15:57:13.908 -> 204F5554505554204F464620000.
15:57:13.908 -> 7474747475747474757574747400.85627.
15:57:13.908 -> 204F5554505554204F464620000.
15:57:13.908 -> 7574747475747474747474747400.85136.
15:57:13.908 -> 204F5554505554204F464620000.
15:57:13.908 -> 7475757474747475747474747500.86854.
15:57:13.908 -> 204F5554505554204F464620000.
15:57:13.908 -> 7574757474747475747475747400.86554.
15:57:13.908 -> 204F5554505554204F464620000.
15:57:13.908 -> 7574757574747474747475747400.86043.
15:57:13.908 -> 204F5554505554204F464620000.
15:57:13.908 -> 7574747474757574747475757400.86556.
15:57:13.908 -> 204F5554505554204F464620000.
15:57:13.908 -> 7574747474747474747574747500.86556.
 

Offline floobydust

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Re: HP 34401a DMM with leaking segments
« Reply #202 on: February 29, 2024, 06:41:01 pm »
How are you doing the level-translation, do you have a schematic? Just to see if that is the problem.
I would also ensure the radio is turned off to prevent TX packets from making interference and power system spikes, in active mode it can spike to 250mA.
I have the rotary encoder bits reverse-engineered somewhere and will look for that when I get a chance.
 

Offline mmx01

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Re: HP 34401a DMM with leaking segments
« Reply #203 on: February 29, 2024, 07:28:37 pm »
With ESP32? Level shifting is not needed, IO is 5V tolerant.
 

Offline floobydust

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Re: HP 34401a DMM with leaking segments
« Reply #204 on: March 01, 2024, 01:24:28 am »
With ESP32? Level shifting is not needed, IO is 5V tolerant.

No mention of 5V tolerance in Espressif datasheets "3.6V max" so I treat it as that. The hiccup looked periodic in the video, happens at a regular interval so something else must be at play.
Changing to the STM32, one way to solve it.
 

Offline mmx01

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Re: HP 34401a DMM with leaking segments
« Reply #205 on: March 01, 2024, 05:51:53 pm »
You are right about the datasheet, for official use I would not push it. For hobby I did many times and "the internet" is full of statements it does. While it is not in the datasheet, it does support 5V when VCC is 3.3V.

As to how I would approach level shifting, resistor dividers may not be fast enough and when I play with FPGAs and 5V->1.8V (older 5VCMOS or TTL logic) I resort to gtl2000dgg. Quite fast for such projects at 33MHz, bi-directional without direction pin, with minimal passive components to get going. Issue is the package is not breadboard friendly so it was cheaper to get STM32 dev kit than ordering level shifting PCB. Once I get the PSU running for business I may come back to ESP32 as project and implement level shifting because it is still unclear to me why ESP32 would struggle with this task, bit banging with timing logic.

Nonetheless it is impressive how much thought qu1ck put into his project. Also trimmed display library with parallel interface where he writes via registers makes it very efficient. I managed to hit the limit with the i2c oled today :)  when pressing buttons fast my oled is freezing and the red light is on.  It seems not possible to write directly to memory of SSD1306 via i2c so I am getting also parallel interface oled to move on.

M.
 
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Offline floobydust

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Re: HP 34401a DMM with leaking segments
« Reply #206 on: March 02, 2024, 01:18:13 am »
An Espressif guy mentioned it works with 5V input but was a bit leery about lifetime of the silicon as it's not tested up there.
There was no need to bit bang with the STM32 but yes with the ESP32? I also thought it could keep up but it does have a kernel and FreeRTOS in the background that might be the problem.

Do you have a running front panel board connected, while snooping the data stream? It sounded smashed up.
I ask because there is a watchdog between the front panel MCU and main CPU. No response from the FP causes the main CPU to issue a RESET (IGFPRES) and beep as well. I thought that could cause the glitch you kept seeing but no.
 

Offline mmx01

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Re: HP 34401a DMM with leaking segments
« Reply #207 on: March 02, 2024, 10:59:19 am »
I have the FP connected and sniff in parallel to the actual communication. Some buttons do work but overall its condition is as seen...

2046281-0

Since entire front is destroyed buying the shell with buttons, PCB and VFD would cost more than what I paid for the device. So my plan is to get this to a working state with oled and 3d print the front with likely new pcb with push buttons.

Encoder was also destroyed (in fact it split into two parts) but mechanically it turned out okay so I put it back together.
 
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Offline trobbins

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Re: HP 34401a DMM with leaking segments
« Reply #208 on: March 05, 2024, 05:52:46 am »
iMo, did you progress with a simple and practical way to de-energise the display filament? 

I want to operate my meter for logging, and the display is showing some intensity variation, so I have some incentive to turn the display off as well as de-energise the filament - for the purpose of lowering internal temp rise, and prolonging useful service life of the display.  The assumption would be that de-energising the display filament has some correlation with display related failure/degradation. 

A concern could be if mains power is toggled, and the meter turns back on with display enabled (which I assume happens due to volatile memory), and that may add risk if the filament is otherwise switched off.   I guess a mains power latched contact could remove that risk.
 

Online coromonadalix

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Re: HP 34401a DMM with leaking segments
« Reply #209 on: March 05, 2024, 11:16:01 am »
you could use the internal front rear switch lever / rod  to actuate a switch ? 

if you dont use the rear inputs,  a front rear movement could activate a filament switch ?  some push lock and push unlock  ??

just tie wrap something on the lever, but be careful not to damage it ?  they get slightly fragile on both end
 

Offline Cyclotron

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Re: HP 34401a DMM with leaking segments
« Reply #210 on: October 27, 2024, 03:52:34 am »
Any chance this modification can be used on a HP 34410a. I've tried finding a replacement VFD but no luck.
If it hasn't been done already, maybe I can get some time to do the work for 33410a.  I can start by modifying one of my 33401a units with what has been done I guess and learn from that.
 

Online coromonadalix

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Re: HP 34401a DMM with leaking segments
« Reply #211 on: October 27, 2024, 08:15:40 am »
cut the vfd filament power is possible, or a display off command if there is


the 34410a  vfd clone(s) are available and work good, they became more expensive since covid,  but a good investment

i had a 34410a  and changed the lcd,  worked very well,      it is not the same as the 34401a

34410 34411a  share the same designs  for the lcd, just acquisition speed are different

just need to be very very careful, they come with long pins, once put in place, they may kick on the front panel  when you slide the pcb in place


an original 34401a  lcd came with the front pcb and was sold at almost 200USD  from Keysight when they had it ...
« Last Edit: October 27, 2024, 08:21:00 am by coromonadalix »
 

Offline robert.rozee

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Re: HP 34401a DMM with leaking segments
« Reply #212 on: October 27, 2024, 02:49:35 pm »
iMo, did you progress with a simple and practical way to de-energise the display filament? 

I want to operate my meter for logging, and the display is showing some intensity variation, so I have some incentive to turn the display off as well as de-energise the filament - for the purpose of lowering internal temp rise, and prolonging useful service life of the display.  The assumption would be that de-energising the display filament has some correlation with display related failure/degradation.

this is something i've been thinking about for a while too. is there concern that just removing filament power is not sufficient to prevent wear?

i see that the 34970A has software control over the filament power, see the below abridged schematic from the manual. this suggests that a simple 2-pole relay (possibly with a pair of diodes added to match the substrate diodes in the MOSFETs that the 34970A uses) may suffice. does anyone have a 34970A on which they can check if drive is (or is not) also removed from the anodes and grids?

the question then just remains as to where would be an appropriate place to fit a switch? on the front, or hidden on the rear panel perhaps?


cheers,
rob   :-)
 

Online coromonadalix

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Re: HP 34401a DMM with leaking segments
« Reply #213 on: October 27, 2024, 04:01:13 pm »
well for a 34401a    if you never use the back plugs,   make yourself a new switch rod and a filament pcb interface ?? 

that way you are original,  and use the hidden front back as a filament switch  loll
 

Offline iMo

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Re: HP 34401a DMM with leaking segments
« Reply #214 on: October 27, 2024, 04:16:37 pm »
iMo, did you progress with a simple and practical way to de-energise the display filament? 

Nope, I did not, also thinking where to put the switch. I run my 34401 always with the display off (as I get the DMM data and 2 temperatures from serial off a stm32 via a Bluetooth into my logging app in my old smartphone), but the filaments are still powered on. I've been planning to put the stm32 (or whatever MCU) inside the meter and switch on/off the filaments via a relay upon a command, but no progress so far..  ::)
« Last Edit: October 27, 2024, 04:18:59 pm by iMo »
Readers discretion is advised..
 

Offline Cyclotron

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Re: HP 34401a DMM with leaking segments
« Reply #215 on: October 29, 2024, 01:59:03 am »
the 34410a  vfd clone(s) are available and work good, they became more expensive since covid,  but a good investment



Do you have a source for the 34410a VFD clones?  I have tried several places and a couple ebay sellers that show they have them say they don't when I contact them for pictures since they almost never picture the proper 34410a VFD.
 

Online coromonadalix

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Re: HP 34401a DMM with leaking segments
« Reply #216 on: October 31, 2024, 08:01:12 am »
 hi  for the 34410 vfd   they camed from aliexpress, i bought them when they came out on the market at a 35$ usd each   ... now .... ???

for a 34401a, it was from Ebay .. china ...
« Last Edit: October 31, 2024, 08:02:48 am by coromonadalix »
 

Offline gamerpaddy

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Re: HP 34401a DMM with leaking segments
« Reply #217 on: October 31, 2024, 08:16:23 pm »
i replaced the vfd on 3x 34401's now with these: 34$ aliexpress ones, https://de.aliexpress.com/item/1005006244217620.html
two HP, one Agilent. both front panel versions. also swapped the flex cable with a proper jst plug.

they all worked flawlessly
(one also got a new front panel sla printed https://www.thingiverse.com/thing:6716036
Before:
2420481-0

after:
2420489-1
2420493-2
2420497-3
« Last Edit: October 31, 2024, 08:21:12 pm by gamerpaddy »
 
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Online mawyatt

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Re: HP 34401a DMM with leaking segments
« Reply #218 on: October 31, 2024, 09:29:28 pm »
i replaced the vfd on 3x 34401's now with these: 34$ aliexpress ones, https://de.aliexpress.com/item/1005006244217620.html
two HP, one Agilent. both front panel versions. also swapped the flex cable with a proper jst plug.

they all worked flawlessly
(one also got a new front panel sla printed https://www.thingiverse.com/thing:6716036
Before:
(Attachment Link)

after:
(Attachment Link)
(Attachment Link)
(Attachment Link)

Nice work :-+

These displays work with the older HP34401A with the All Red Terminals?

Best
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 

Offline gamerpaddy

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Re: HP 34401a DMM with leaking segments
« Reply #219 on: October 31, 2024, 10:12:43 pm »
For me it did, yes.
the front panel pcb were different
one contained a big dip NEC job
the other one two four sided ic's
« Last Edit: October 31, 2024, 10:14:54 pm by gamerpaddy »
 
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Online coromonadalix

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Re: HP 34401a DMM with leaking segments
« Reply #220 on: October 31, 2024, 11:55:30 pm »
normally they are compatible for both

its the same glass ...  but different drivers ...   :-+

lucky for us the design leaked and was copied ....
 

Offline amp

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Re: HP 34401a DMM with leaking segments
« Reply #221 on: November 12, 2024, 08:02:18 pm »
I just finished this modification to my HP34401A as my DMM also had an issue with leaking segments.

For the connections to the OLED DISPLAY MOD PCB by QU1CK:
- GND (W601-P1 = GND)
- VCC (W601-P3 = +18V) I read in this thread that sourcing the voltage from VCC (generated by U553) could be better so this could be checked. If you do this, you need to make a connection to the main PCB.
- SI    (W601-P2 = FPDO)
- SO (W601-P6 = IGFPDI)
- SCK (W601-P4 = IGFPSCK)
- INT (W601-P10 = IGFPINT)
All connections soldered in parallel to the 12pin ribbon cable on the front panel PCB. (Reference names added above are from the HP34401A service manual
 
I used the firmware_nobootloader.bin (v1.1). This was directly flashed to the STM32 by temporarily connecting my programmer to the SWD interface and programming the binary at address 0x08000000.

I thought of just sharing the information regarding the pin connections as it could help someone else who wants to implement the mod.

Thanks QU1CK for this mod.
 
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Online mawyatt

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Re: HP 34401a DMM with leaking segments
« Reply #222 on: November 15, 2024, 05:30:44 pm »
For me it did, yes.
the front panel pcb were different
one contained a big dip NEC job
the other one two four sided ic's

Just replaced the display in our old HP34401A with Red Terminals (has NEC DIP). Not having the proper desoldering tool (just wick and the cheap hand plunger) we opted for a Yihua 929D-V.

The replacement display was from AliX and slightly different than the OEM, but we had little trouble replacing the fading OEM one.

https://www.aliexpress.us/item/3256806057902868.html?spm=a2g0o.order_list.order_list_main.23.7380194dxSFr2T&gatewayAdapt=glo2usa

The Yihua made quick and easy work of removing the old display and left the PCB is good shape!!

Anyway, thanks for the info and as you can see these replacement displays work with the older Red Terminal HP34401A.

Best
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 
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