| Electronics > Repair |
| HP 34401a DMM with leaking segments |
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| coromonadalix:
Qu1ck told me the pinouts used are in parallel of the falt ribbon cable here's the answers he gave me : I took power from floating 5v, output of U553. Your other option is to take it from input of that regulator, in that case you are less likely to feed any switching noise from oled screen (it has a built in boost converter) into multimeter, but I highly doubt that matters in any way. My measurements did not show any noticeable impact. But if you take it from input you will be on the limits of lm1117 power dissipation with the polygon I have for it on the board. You can stick small piece of metal as heatsink on it or better yet rip out the boost converter from the screen and feed higher voltage into the panel directly. That will limit current consumption of the front panel converter (my board) and eliminate any switching noise. But I didn't bother, total current consumption of my board + oled screen is 60-70 mA. If you feed 5v into lm1117 it will be just fine. Just don't take it from +18v becase a) it's used in sensitive analog stuff and b) voltage drop for the regulator will be too high. FPINT is not currently used Send him an email if you need some help, in a month i'll order the lcd to try this project for myself too, i have a nice 34401 to play with. But he told me his project is not tested with the newest pcb version having the 75518 vfd driver ... i have 2x 34401a with this pcb |
| justanothername:
--- Quote from: coromonadalix on December 30, 2018, 04:58:30 pm ---Qu1ck told me the pinouts used are in parallel of the falt ribbon cable --- End quote --- For testing purposes i was powering the PCB with a laboratory power supply. Powering was ok, I could even see the resonator working at 8MHz. I checked all the solder joints end even probed with the scope on the MCU pins, the signals were present. I managed to use the jlink with SWD in platformio and flashed the program without bootloader. Aside from the bargraph beeing drawn, no data was displayed, just as before. The last thing before I reassembled the unit was that I tried every possible permutation of the cable connection. I used these contacts at the flat ribbon connector: GND (1) IGFPDI (4) - tried at MISO and MOSI and INT IGFPSCK (6) - connected always to SCK IGFPDO (2) - tried at MISO and MOSI and INT IGFPINT(10) - tried at MISO and MOSI and INT As I can see in the service manual, there is also a version of the display board with an 80C51 microcontroller. Idk if I can determine the used components without desoldering the VFD, but maybe there are different protocols used in later versions. For now I will leave the VFD soldered in, as it is fully functional, but a little dim. For the powering situation, another way is to use -13V as VCC and -18V as VDD (gnd). Then use the outputs of the comparator U607 as inputs to the OLED-board. Both (-18V and -13V) should then be fed through some ferrites. Since the OLED panel got boost converters on it, it may be necessary to add some additional shielding. Maybe i will try to improve the EMI radiations of the converter. The usual methods would be to increase output capacitances, to add shunt capacitors from in to out, or to change in/out capacitors to lower-ESR types. But first things first, the next goal for me is to actually see something on the display. |
| coromonadalix:
For the front panel, if you look on the back pcb and see two dip rows of soldered pins + the ribbons and vfd pins ... youll know that you have the nec unobtanium display ..... The newest version has only the vfd rows pins and the ribbon pins and pn: 66512 sticker on it, my other pcb vfd doesn't have the sticker ?? sn : us3610xxxx sn: 3146-A75xxxx Both have the firmware : 10-05-02 ?? Version: 06-04-01 and lower = old pcb Version: 06-04-02 and higher = new pcb Once again, qu1ck wrote not tested with the newest pcb version VCC (2) floating 5 volts output of U553, i would not dare to poke on the +/- 18v lines they are for the measurements sections ... it could affect the meter ? GND (1) IGFPDI (4) - should be MOSI IGFPSCK (6) - should be SCK IGFPDO (2) - should be MISO IGFPINT(10) - should be INT but not used ??? We see clairly (picture attached) he used 5 pins on his pcb, not the 6th (int) |
| coromonadalix:
Oh i think we need the adafruit gfx librairies to compile it ?? The only thing i have on hand is the stm32 blue pills boards, they are arduino IDE compatibles ... I have received from Qu1ck one of his pcb, but don't have time to assemble it right now, too many projects on hand, and i go on vacation january 10 There is an firmware.bin (attached) who is already compiled .. try this one The other firmware_debug.bin (attached) spit out on serial some data ?? He wrote : the eeprom is not needed for now ?? |
| justanothername:
--- Quote from: coromonadalix on December 30, 2018, 06:46:32 pm ---The newest version has only the vfd rows pins and the ribbon pins and pn: 66512 sticker on it --- End quote --- This seems like my version (attached pic). I can confirm that I tried the configuration you described and it does not work. Do you know if the panels are interchangeable across versions? If not, then it is obvious that there are protocol differences. For the firmware: I use the STM32F103CB with double flash size, so I recompiled the project for this controller. However, it should be no problem to flash a firmware compiled for C8 straight onto the CB. As for the adafruit gfx libraries, you can load them with Platformio within VSIDE, but you need to manually delete SPITFT as stated in his howto.md. here is the modification to platformio.ini for my board: --- Code: ---[env:release] platform = ststm32 framework = arduino board = genericSTM32F103CB board_build.variant = custom debug_tool = jlink upload_protocol = jlink --- End code --- firmware attached. |
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