Advantest R6581 Service Manual

[TheDefpom]

I was thinking that there must be an ASCII data stream somewhere to grab the measurement data from, rather than trying to decode the screen data, probably the same for the mode data too I expect, I mean the data is viewable over GPIB so it must be in a raw format somewhere other than the screen.

[Mickle T.]

The front panel interface is not a serial or parallel interface in the usual sense. In fact, it is a shared memory area that can be accessed asynchronously by both the main assembly processor and the front panel processor.

As far as I know, the first 47 bytes of external memory on the H8 MCU side are a serial buffer of character codes for the 1st and 2nd lines of the display. The next 18 bytes are the annunciators flags (0x00 - off, 0x01 - on).
But besides this, the same memory contains a keyboard buffer, a matrix of pressed key flags, an interrupt messaging mailbox, and a large number of flags, the purpose of which I do not know (most likely they are related to scrolling, blinking, etc.).
The H8 MCU firmware contains a character generator with the standard ASCII character set, however, I found that characters with codes 0xE0...0xE8 and 0x7F are used in debug mode to smoothly fill the display with vertical and horizontal lines.

[Mickle T.]

I decided to take a chance with my working multimeter and test the translator with the first monochrome OLED display that came to hand (Winstar WEH002004 in graphic mode).
Apparently I’ll still have to look for another R6581D/T, or wait until the display on my multimeter completely goes out

[picburner]

I have an R6581T also with a practically invisible display. I was thinking of doing a similar job to what Mikle is doing using a Futaba GP1294AI 256x48 VFD, basically it is a COG that incorporates SPI input logic and HV drivers and is currently sold at a very affordable price.
The dimensions of the display are similar to the pre-existing VFD but, to do a job well done (and to fit in the limited space), I would have to redo the entire original PCB.
I've already done similar work for a Wavetek 1271, but in that case I really had no other choice.
In this case, however, I'm a little hesitant: is it really worth doing all this work?

[Mickle T.]

I think the GP1294AI is the perfect solution. If the indicator is suitable in thickness, it can be connected with a thin flexible cable to an external mezzanine board on which the microcontroller and high-voltage DC-DC can be placed. A complete redesign of the entire PCB carries the risk of damaging the H8/322 microcontroller, the firmware of which is not yet available.

[branadic]

Thanks to MickleT., who deserves all credits, we have a wonderful service manual. I was wondering, why noone has reported INL improvement just yet? Maybe the math is too much of a hurdle?
Hence why I've put together this simple spreadsheet, hoping that more people will benefit from MickleT.'s wonderful work and report their success here.

I've tested the spreadsheet myself against our 3458A and an ADR1399 upgraded AN3200, taken readings with H0 ... H15 reset, calculated the new constants, copied them into the device using Python and rerun the INL test. Attached are my results.
Obviously summer time is not the best time to do this, even if the lab is AC stabilized. But the windows are facing south and temperatures outside were quite high, so there is quite some temperature change during the measurements. However, even with that drawback INL turned out <±0.1 ppm.

I hope that motivates people to get their R6581(D,T) INL down too.

-branadic-

[leighcorrigall]

I'm relocating at the moment. No lab to perform measurements/adjustments. I have 2x 3458As that I can use for a linearity adjustment

I will reply again when I have time to review the manual and the scripts. I agree, the first time I read the manual, it was difficult to understand the heaviside functions.

[Mickle T.]

Announcement of the next update.

[branadic]

Wow, great progress, I'm in for one

-branadic-

[TheDefpom]

Indeed that looks very good, I picked up a couple of different displays, I haven’t got around to trying to do anything with them yet though. I may not need to if I can buy these from MickleT, or just hook up a pro mini and dump some code into it.

Good to see the larger display can simply be plugged into the other units connector and it just works.

[gamalot]

I've also thought about DIY replacement display, but it seems difficult to find one with the right aspect ratio.

[bsw_m]

I found this display. It fits in place of the original pretty well.

[chekhov]

One more alternative could be this display:
https://www.buydisplay.com/bar-type
-4-58-inch-320x960-ips-tft-lcd-display-spi-rgb-interface

It has the same dimensions as the one above, but less colors and maybe a bit lower contrast.
I have both of them but haven't compared yet, wanted to revive my failed Keithley 200X display replacement project.

[bastl_r]

Hi

The link does not work for me with the line break.
Here without now.

https://www.buydisplay.com/bar-type-4-58-inch-320x960-ips-tft-lcd-display-spi-rgb-interface

[gamalot]

Thanks guys, I just ordered two 4.58" LCDs to see if they will fit. 

[dietert1]

Thanks for the hints. I found those bar displays at digikey, 1528-5805-ND. They don't have display memory, so i ordered STM32H730 MCUs that can drive the display with their LTDC peripheral. They have enough RAM to hold a 1-byte per pixel memory, so 256 colors with a programmable color lookup table (palette).

Regards, Dieter

[Mickle T.]

The first post has been updated.
A new topic about replacing the display has been created: https://www.eevblog.com/forum/repair/advantest-r6581-vfd-replacement/msg5634443/