HP 3468a multimeter LCD pinout - Page 1
Forum section: electronics / repair

author: Dan Moos
author_rank: Frequent Contributor
timestamp: May 07, 2023, 04:20:55 pm
content: The meter in question has a blank display. Originally, the cable seemed damaged, so I hardwired the thing. I'm uncertain if I got my wires correct, if I damaged the display, or it's a problem with meter itself. I do have the service manual, and have confirmed as many things are working as I can. The only thing I can't see is the phase 2 clock, which comes from the MCU. Hopefully that doesn't mean bad. MCU, but I will debug that too. Every other pin on the thing seems right so far.Anyway, I found a display ( hp 5061-5212) on ebay. Before I install it, I wanna do tests on the original to see if it works. The service manual explains the clock, sync, and serial data and instruction lines, but there are 16 lines going to the LCD, most of which I'm not sure what they do. I also have no idea what the instructions are, or the protocol used for instructions/data. Also, Whilst I can ID the known pins on the motherboard, I lost the original cable, so I don't for sure know how they map on the LCD end. Can't find another cable online, but would love to have one!What I'm looking for is more info on the pinout of the lcd

author: cruff
author_rank: Regular Contributor
timestamp: May 07, 2023, 05:20:08 pm
content: As for the cable from the motherboard to the LCD, it's just a 1-1 parallel ribbon cable.I've not seen the display protocol documented anywhere, but the CPU firmware is available if you want to go through the effort to disassemble it to see how it interfaces to the display.

author: Chris56000
author_rank: Frequent Contributor
timestamp: May 07, 2023, 07:26:29 pm
content: :=\Hi!It's not too difficult to determine the pinout of a multiplexed LCD – there is a circuit in one of the "Elektor 300 Circuits" series of books for an "LCD segment tester" based on a 4047, unfortunately now that the rotten copyright moguls have crawled out of the woodwork in recent years it's much more difficult to find these books!However, if the "Blackplane" or "COM" pins are indicated on the '3468a service manual, all you need to do is connect one output of the '4047 segment tester to one of the "B.P." or "COM" leads, and the other output to the remaining connections on the LCD – when you find a com/segment connection pair the element will go dark just as if you were testing a seven–segment LED unit, then you can identify the pins – the usual way is to draw a table with rows for each "B.P." or "COM" pin and columns for each other undetermined LCD pin, then as you test along in order you'll be able to fill in which pair of pins drives which element!PS!Found it :–https://www.learningelectronics.net/circuits/liquid-crystal-display-lcd-tester.htmlChris Williams

author: Stray Electron
author_rank: Super Contributor
timestamp: May 07, 2023, 07:37:14 pm
content: I THINK someone on this forum converted a HP 3478 LCD display to a 7 seven segment LED display. I expect that the 3468 and 3478 displays are very similar. You might want to search for that thread.

author: cruff
author_rank: Regular Contributor
timestamp: May 07, 2023, 08:18:53 pm
content: The 3468A LCD board has two controller chips mounted on it and it appears there is some kind of clocked data/command signalling going on from the schematic. The motherboard does not drive the seg/com signals directly.

author: Halcyon
author_rank: Unknown
timestamp: May 08, 2023, 02:45:03 am
content: Merged duplicate topics.