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This "bring some color to my 8757E" upgrade project started early this year scraping the internet for documentation and firmware of C or D versions of the 8757 and all references to this instrument. One of the contacts found was Tony, (via tgsoapbox) and he helped with great commitment? to provide me the firmware of 8757D rev 6.3. Many thanks Tony!

Just programming some EPROMs with the "D" version and swapping them in my "E" didn't work and was the starting point to compare the E's software to the D.
I used the dissasembler Ghidra to analyze both software versions in program flow, memory adressing and routines. Adapting the code and after each change, Easy68k was used to test the code and calculate a new ROM checksum before running it in my 8757E hardware. During these investigations I also found some discrepancies in the HW addresses as specified in the service documentation of the 8757C / D.?
Alan Clements' book Microprocessor System Design for 68000 also came in handy understanding the hardware design and processor interfacing.

The GSP software of the E version is different (longer in code) from the D and also some other types such as certain 8753s that use the same GSP hardware. Suspecting that this is where the conversion to monochrome is performed I tried to integrate a 8757D GSP firmware section with the E software, that was not a success and this option was quickly abandoned.
To cut a long story short, many routines such as boot cycle, loading the graphics processor software, ROM checksum and system check procedure have been step by step analyzed and handwritten to solve this puzzle.
Tracing the system check and resulting error code messages? is where the graphical program flow display in Ghidra came in handy, I found the routines in which these hardware items are tested and stored in the processor stack values ??to test the instrument type with the hardware version. (Later in the process?I discovered a corresponding address reference instruction in the calibration software proving that this is indeed the solution to the HW and FW options).

During the first operational tests with connected 8350B, strange errors occurred resulting in HPIB code / command errors and random locking up the system. I expected upgrading my 8350B from release 3 to 7 would solve the problem, some delay arose because correct type of EPROMs had to be ordered first as I didn't want to erase the originals at the time.
The release 7 upgrade unfortunately did not solve the problem and I had to go into the 8757 firmware again, I discovered that due to my changes there was a problem with the interrupt handling of the HPIB interface. After this was solved everything works fine, but my advice is to use the software version 7 firmware in the HP8350B as it has not been tested back to FW release 3.

The many times of UV erasing and programming seemed endless and to speed up erasing and programming I switched from the original D27010 EPROMs to the W27C010-70 EEPROMs, these are pin compatible and work perfectly.
This E to C firmware based on the REV3.2 has all options of the C version, the D firmware works, but the overall implementation is still a problem due to the hardware differences of the front panel with regard to a date / time clock provision and differences in addressing and interrupts. I'm still working on that ...

Normal measurements and most special functions such as masks, plotting and saving have been successfully tested, all that remains is to connect it to HP diskdrive and HP9000.

I will upload the EtoC EPROM bin files, just program some (E)EPROM's and swap them into your "E"? without any further changes it should run like an "C" REV3.2

The inserted picture shows a simple triplexer test, misusing the R input as 3th channnel, but it is working and looks a lot better than the old green (hi)


The next project is to analyze the routine of the calibration software and extract the cal factors for the channels. I also want to try if it is possible to calibrate the channels using a 3325A and some extra's to generate the needed reference signals.

As the last remaining hardware option, it would also be nice to add channel C. So if someone has a spare 08757-60058 A7 Circuit Board available,? please notify me.

Open for questions or remarks,
Best regards,
PE1MHY, Guido

Hi Akild,

I am curious about your experience with the 27C1001.

Before I started the software I made a small hardware adjustement to the GSP board to simulate the rear panel A16 board. It is a GND jumper pin 3 to pin 5 of J2 of the GSP board, during testing I did not notice any issues without this modification.


I have also ordered A7 board, and found I think the correct chassis connector.
From all firmware information I have gathered all options should be inside and only extra's are to be found in the 8757D release(s).
But then we have a difference in hardware like the missing realtime clock IC on the frontpanel.
I don't think we are going to miss this option as it only ensures that a date & time is automatically added to a file saved on disk.


BR, Guido

I should have mentioned that in order to convert an E model to a C model (monochrome to color), you also need to use the C model EPROMs.

While it was a group effort, I wrote part of the 11613 calibration program for the 8757, it is in HP BASIC (RMB).? The 11613 was designed by "KA" and he wrote all of the control software for it. You can download the cal program from here: It is about 3700 lines of code but much of it is unrelated to the actual calibration; such as plotting, testing of the 11613, manual settings, etc.

The 11613 provided individual steps of 0.5db attenuation of a 27.8KHz signal from 0 (10.6vpp) to about -154db.?? Keep in mind, this is dBv, not dBm.? The program would cycle through each step and measure the resulting power from the loggers.?

Trying to calibrate the 8757 without an 11613 would be very difficult, but since we will be dealing with Covid for many more months, maybe you will have time to try.? From what I have seen, the calibration of the loggers seems to be pretty stable, so I am not sure it would be worth the effort.

Thank you very much Ceasar!
That is valuable information and we must be able to go a lot further with it. The tip to find a curve fitting table from the existing calibration values is also a good option, at least to get the C channel functional quickly.

I am curious to read the data and to be able to confirm and fit it to your CAL-EEPROM memory location format below. I'll try loading the Cal-prog into my HP9000-300 or 332 and see what can be achieved with it.
In anticipation of the arrival of my ordered A7 board, I had already started using my 3325A + additional attenuations using a 11713A setup and testing the amplitude range and linearity of this setup using 34401A and 54100A.


I will keep you informed of the progress.

Thanks, Guido

Thank you very much Ceasar!
That is valuable information and we must be able to go a lot further with it. The tip to find a curve fitting table from the existing calibration values is also a good option, at least to get the C channel functional quickly.

I am curious to read the data and to be able to confirm and fit it to your CAL-EEPROM memory location format below. I'll try loading the Cal-prog into my HP9000-300 or 332 and see what can be achieved with it.
In anticipation of the arrival of my ordered A7 board, I had already started using my 3325A + additional attenuations using a 11713A setup and testing the amplitude range and linearity of this setup using 34401A and 54100A.


I will keep you informed of the progress.

Thanks, Guido

Hi all,

Here is an update on adding a C channel to my HP 8757'C'

The board I bought is a 08757-60058 (looks like 1986 IC's on it), the original boards in my 8757 are 08757-60087 (looks like 1994 IC's on it), so the one I bought is a bit older.

When I put the card in the empty C-slot, I do get the channel-C in the menus. But I did not see anything about default calibration being used for the C-channel.

And I only got a flat line at -35dBm, no matter if there was a detector connected or not, or if the detector has a signal or not.

So first I thought that I might have received a bad board, but I then tried the board in the A/B/R locations, and there it works fine.

Compared the calibration when trying the different locations, and none is a perfect match, but the R-channel is the closest, with only a small offset.

Then I did check the ADC-test in the service menu, and there the C-channel behaved the same way as the A-channel, the data voltage changed the same when having no probe connected, and connecting a probe.

I then suspected the calibration data for the C-channel in the eeprom was the problem. I had already desoldered the eeproms and read the content.

All data was 00, except for ID, date and checksum (last 8 bytes of the cal data range), maybe if I had zeroed those, I would have gotten default calibration values.

Then I made new eeprom files with a hex editor, by copying the R-channel to the C-channel space in the files, programmed the eeproms and tested it, and it works great? :)

So now I have a functional C-channel, but not calibrated.?

If anybody can share their eeprom data from their 8757C/D/E, It would be great!

Then I could try other calibration data, and maybe get an even better match to my board.

I have included my unmodified eeprom files in the zip file containing the 8757E firmware that I have uploaded to KO4BB.

I still need to get the connector and make the cables to complete the upgrade.

Br,

Askild

Greetings, Forum.

Reviving this thread...

I managed to acquire a fresh 8757E and noticed that EPROM Upgrade binaries from "E" to "D" was available
on KO4BB. The instrument I got has a CRT monitor.

Any benefits by upgrading the firmware from "E" to "D" even if no C-Channel is installed
and the two added buttons on the "D" are not added?

Cheers

Ulf Kylenfall
SM6GXV