Upgrading the HP/Agilent 8714C from green CRT to color LCD

[coromonadalix]

Nice 

[AF6LJ]

Nicely Done!
I have a Marconi service monitor I need to do that mod to.

[KrudyZ]

Nicely Done!
I have a Marconi service monitor I need to do that mod to.

Well, I haven't really done anything, yet.
The hard part is still ahead, milling the inside of the front panel flat.
It is concave to match the curvature of the CRT, but the LCD is of course flat.
Luckily, I have a milling machine available, which should help a lot.

[AF6LJ]

Nicely Done!
I have a Marconi service monitor I need to do that mod to.

Well, I haven't really done anything, yet.
The hard part is still ahead, milling the inside of the front panel flat.
It is concave to match the curvature of the CRT, but the LCD is of course flat.
Luckily, I have a milling machine available, which should help a lot.

Simple operation for you.
The set-up on this would be interesting to see.
Hopefully that bezel is some kind of metal; I would be a bit afraid to mill on thirty plus year old plastic.

[TheSteve]

The front is plastic, it mills beautifully - even with its age. This is such a huge upgrade for this NA, the color LCD really makes it a pleasure to use.

[AF6LJ]

The front is plastic, it mills beautifully - even with its age. This is such a huge upgrade for this NA, the color LCD really makes it a pleasure to use.

Very cool looks Great.

[eb4eqa]

Well done! It looks great. 

Roberto

[KrudyZ]

I ended up using a router table instead of the milling machine, since the plastic is flexing and generated chatter on the mill.
It was pretty easy to maintain a steady downward pressure on the router table to avoid the chatter.

[AF6LJ]

I was wondering how a mill would work given that peace would flex a lot.

[KrudyZ]

I put together the LCD module with some laser cut acrylic, a frame and a back board with holes to mount the electronics.
The only custom part is the 20 pin header to VGA plus power adapter board. I did not make any mods to the video converter board.
I was toying with the idea of keeping the VGA cable connection and not going through the ribbon cable. In retrospect I wish that I had done that as I soldered the red coax to pin 2 instead of 1 of the 20 pin header AND DID NOT CHECK MY WORK.
That shorted the red channel to the 12 V supply and blew up its channel on the video DAC plus a protection diode
It's an obsolete part, but available on ebay. The green and blue channel are still working, so I can still use the instrument, but damn annoying to make such a silly mistake.
As an aside, on my board the protection diodes for the VGA are individual dual diodes. The schematics show one big 14 pin device to protect all the lines. At least I got lucky on that one as it's easier to replace...

[KrudyZ]

In the last picture you can see that I am using the original CRT mounting studs and its washers and nuts as a spacer.
The acrylic has matching holes to align the LCD. The LCD assembly is simply held in by the front bezel pushing it onto the studs.
Really easy to take apart that way.

[AF6LJ]

That looks really nice.  Great work.

[KrudyZ]

Yesterday, I got a replacement for the video DAC I had blown up by connecting the red channel to 12V instead of the adjacent pin on the ribbon cable where it was meant to go.
I snipped out the broken DAC which was the easiest way to remove it due to its PLCC44 package.
With the new one in place I got the exact same problem, say what?
Turns out that my replacement protection diode I had put in earlier wasn't a BAV99 as its bag label suggested, but a common cathode dual, so the red channel was now shorted to the 5V protection rail.
Just goes to show that you have to check everything... Luckily, this did not kill the DAC since its output is a current source and the part runs off of the same 5V.
After replacing the diode with a real BAV99 I finally got my red channel.
Now all looks good. Still waiting on getting the LED strips for the backlight.

I'm a bit shocked that the little 75 Ohm source termination resistor survived having 12 V across it, i.e. almost 2W of power... There wasn't even any discoloration.
Interesting side note, the VGA to LCD converter goes through some kind of calibration to measure the incoming video stream and centering the image. It also seems to be doing some black and white level adjusts. You can actually see the image quality improve over the first few seconds after turn-on.

[AF6LJ]

Very nice  Love it.

[BFX]

Excellent! 
I'm still curious what is difference between my 8713B and 8714C regarding to this color output.
I Haven't time to investigate that yet, but if anybody knows please let's me know.

[rfdes]

I see that this original post is from several years ago but wanted to reach out and see if anyone would be interested in a software patch for a timing issue that I discovered while modifying my HP87xC unit to accommodate an LCD display.

I took the approach of populating the CPU assembly with the LCD display components and using a raw LCD panel (NEC NL6448BC26-03). All went without a hitch and I was very happy with the outcome(almost).  However, I discovered that the default horizontal/vertical timing for 640x480 60Hz was not as accurate as needed  for an LCD panel.  The default timing would leave a white line on the left and top of the screen.  Using the 'CRT adj' controls would not allow precise enough adjustment for an LCD screen.  For an analog CRT it works fine.   The first two pics show the issue that I am describing, i.e. I had no way of accurately centering the image.  I tried using the analyzer's CRT manual entry timing parameters with no luck.  Now most people would say: 'Why bother?' but I could not leave good enough alone and decided to reset the default H & V timing to the proper values.  I reverse engineered the UNIX firmware and created an new version of the C.04.52 firmware that fixes the issue. See Pic 3.  If anyone is interested in my version of the main firmware, send me a PM and I will email you a copy.  I also have patched the Boot Rom to also fix the timing problem during boot.  You're welcome to a copy of my Boot patch also.
Thanks
Jim

[TheSteve]

I don't have my 8714 anymore but you did some great work, I really appreciate you sharing it with others.

[rfdes]

I've owned my analyzer for about 10 years but only recently did I decide to upgrade the LCD screen after reading your original post.  When I first got my unit I had spent some time designing a key-gen for enabling the different options (enjoyed the challenge).  Unfortunately, the Key-Gen option algorithm will not work for enabling the full Vector capability.  You still needed to patch the boot ROM.  I had planned at the time to reverse engr and patch the main firmware so that the user would only need to perform a firmware install in order to enable ALL options plus vector capability. 

Well, while I was working on the timing issue patch, I went ahead and created a modified firmware to force all options+vector.  I guess I should go back and patch the 'A' and 'B' versions as well and then submit them to the HP-Agilent-Keysight-equipment@groups.io.  Not sure anyone would care to use this method, but the hope was that this would eliminate the need to yank out the CPU assembly and reprogram the boot ROM.  Many people don't have access to a device programmer.

Take care -
Jim

[VSS]

Hello

I have purchased an HP8712 and want to replace the CRT screen.
I have read your description and I have a few questions:
1. Can you describe exactly to which pins you connected the RGB signals from the VGA port? I don't see it in the picture.
2. Where is the synch H and synch V signal and power +12V on the tape?
3. How do I remove the picture tube? Do you need to disassemble the coils on the tube?

Thank you for your response
Artur SP3VSS

[VSS]

Hi all

My HP8712 has a new display: D
LCD panel bought on Aliexpress: https://www.aliexpress.com/item/4000328921850.html
Display and driver holder designed in Fusion360 and printed on the Ender3.
Files at https://www.thingiverse.com/vss/designs
Controlling the display by a remote control and an infrared receiver.

Thank you for your inspiration!

[W3AXL]

Hi all

My HP8712 has a new display: D
LCD panel bought on Aliexpress: https://www.aliexpress.com/item/4000328921850.html
Display and driver holder designed in Fusion360 and printed on the Ender3.
Files at https://www.thingiverse.com/vss/designs
Controlling the display by a remote control and an infrared receiver.

Thank you for your inspiration!

Sorry to bump an old thread, but it appears the files for you build are no longer on Thingiverse. I've got an 8712 I'd love to do this mod to, it looks very clean.

Also, which screen size did you end up going with? The Aliexpress link has several available.