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

[TheSteve]

Today I finished installing an 8.4 inch TFT LCD panel in place of the original green CRT in my HP 8714C Network Analyzer.
This mod should work for the 8714C, 8714ET and 8714ES as they all have a VGA out connector on the back.

I bought the LCD panel and VGA driver board from ebay for $80 USD shipped - the seller shipped the entire kit inside a foam crate, it was extremely well packed.
This is the specific auction http://www.ebay.com/itm/191341791384 - I made a best offer to get the 80 dollar price.

The original green CRT runs off 12 volts and uses 1.2 amps of current. The LCD runs off 12 volts and uses 1 amp of current so power wise it was quite compatible.
The VGA out on the network analyzer is 640x480 @ 60 Hz which is the native resolution of the LCD which makes for a very sharp display.

The original green CRT is in a self contained metal cage that pulls out with the main power supply from the network analyzer easily. It is connected via a shielded 20 pin ribbon cable which provides ground, 12 volts, mono video, horizontal and vertical sync. The VGA output is only on the back of the analyzer. Luckily HP left 3 unconnected wires in the 20 pin ribbon cable which is exactly what I needed for the VGA red/green/blue signals. This meant the only mod to the main board itself was running 3 small coax cables with each of the colors from the test points near the VGA connector to the unused contacts on the ribbon cable.

Once the CRT was removed I was left with a nice metal cage to install the VGA controller and a small adapter board I threw together to translate from HP's 20 pin ribbon cable to the video and power inputs of the VGA controller.
I decided to install the board inside of a secondary metal box, it made mounting easy and adding an extra level of shielding is always a positive. The LCD panel is mounted to the same 4 frame bolts that held the original CRT using a pair of adapter brackets I made out of 1/16th inch aluminum. The brackets also allowed me to fine tune the position of the panel as well as adjust the spacing from the front cover.
Speaking of the front cover - the inside of it was molded to match the curvature of the original CRT. The only permanent change I made during this mod to the analyzer was to mill away the curves so it would sit flat against the LCD panel giving it a factory look.

The project so far has exceeded all of my expectations. One last step I plan to do in the future is switch the LCD panel from CCFL back light to LED. That will be one less switching power supply running. I can also make up a circuit using the original CRT brightness pot on the left of the analyzer to adjust the LCD brightness. I did test the radiated noise from the panel and in front of the analyzer with my spectrum analyzer before and after and am happy to report I am detecting no additional noise which will interference with test results.

I figure for the dollars invested this is a pretty nice upgrade. The original green CRT is very sharp and easy on the eyes but the LCD really gives the machine a much more modern look and some color which is nice - btw the colors are all adjustable.

[TheSteve]

Pics of the main board coax cables, LCD brackets, the front cover before milling and the front cover after milling.

[TheSteve]

LCD panel during initial testing and a shot of the what the stock analyzer looks like with the green CRT, some how I didn't end up with a picture showing the panel mounted to the analyzer before I put the front cover back on.

[nidlaX]

Simply brilliant!

[tec5c]

Nice upgrade 

I have been considering looking for a LCD kit upgrade for my 8753A analyser, bit too busy at the moment though.

I did notice that there was some overlapping text on the LCD (best view in the first picture. Marker text for the smith chart overlapping with the j100 coord.), did this occur with the CRT also?

[crispy_tofu]

Fantastic! 

[VK5RC]

Lovely work, well done.

[TheSteve]

Nice upgrade 

I have been considering looking for a LCD kit upgrade for my 8753A analyser, bit too busy at the moment though.

I did notice that there was some overlapping text on the LCD (best view in the first picture. Marker text for the smith chart overlapping with the j100 coord.), did this occur with the CRT also?

Yes, the marker text has always overlapped if you have the right combination of options selected, no change going from the CRT to the LCD.

There are commercial made LCD kits available for the 8753A - not sure how affordable they are though.

I have never seen any kind of LCD upgrade for the 8714 series however while looking through the schematics to come up with my mod I did notice there is a provision for a factory LCD option. The parts are all marked no-load and I don't think they ever sold one with an LCD screen. I did ponder installing all of the parts but it looks like it would also need some firmware support which I doubt is present and the LCD output is 4 bit. The 640x480 panel I bought uses a 6 bit interface.

The LCD kit I bought also has a push button board to configure it, along with an on/off switch etc. The LCD happily powers on with that board not connected and works fine without it. I can remove the front cover of the analyzer and plug it in if needed - to adjust brightness, contrast etc.

[tec5c]

Thanks for the info, most appreciated.

[TheSteve]

The LED strips I ordered 1.5 months ago finally arrived. They are long thin strips of white LED's mounted on PCB. They were shipped in a strong plastic tube to prevent damage yet some how the postal system still managed to fold the tube right over. This of course snapped the LED strips into pieces, they also managed to damage the included switching power supply. The LED strips I ordered were the shortest I could find on ebay but were still too long. As luck would have it the broken pieces were the correct length to convert the LCD screen to LED backlighting and to ditch the CFL tubes and inverter. They were also broken at just the right place as the LED's are in parallel sets of three LED's in series.
The original CFL tubes just slid out with no panel disassembly at all. I added some heatshrink tubing to the LED strips which gave them a nice snug fit when slid in to the LCD panel. For brightness I used a power supply to find what I thought was the optimal drive current and then added a single 20 ohm resistor in series with the LED strips which connect to the 12 volt power supply. So for now the brightness is fixed.
A further project is to use the original 8714C knob to vary the brightness. The pot is 100K so I'll need to come up with a simple linear based circuit(no noise) that can vary the current to the LED strips between 100 and 200 mAh.
Once installed the LCD looked same of course but has instant on backlighting with no inverter noise at all. I have attached pics of the original tubes and new LED strips.

[TiN]

Badass mod, reviving gear like a boss. 

[Zero999]

The LED strips I ordered 1.5 months ago finally arrived. They are long thin strips of white LED's mounted on PCB. They were shipped in a strong plastic tube to prevent damage yet some how the postal system still managed to fold the tube right over. This of course snapped the LED strips into pieces, they also managed to damage the included switching power supply. The LED strips I ordered were the shortest I could find on ebay but were still too long. As luck would have it the broken pieces were the correct length to convert the LCD screen to LED backlighting and to ditch the CFL tubes and inverter. They were also broken at just the right place as the LED's are in parallel sets of three LED's in series.
The original CFL tubes just slid out with no panel disassembly at all. I added some heatshrink tubing to the LED strips which gave them a nice snug fit when slid in to the LCD panel. For brightness I used a power supply to find what I thought was the optimal drive current and then added a single 20 ohm resistor in series with the LED strips which connect to the 12 volt power supply. So for now the brightness is fixed.
A further project is to use the original 8714C knob to vary the brightness. The pot is 100K so I'll need to come up with a simple linear based circuit(no noise) that can vary the current to the LED strips between 100 and 200 mAh.
Once installed the LCD looked same of course but has instant on backlighting with no inverter noise at all. I have attached pics of the original tubes and new LED strips.

Good work!

Here's a constant current LED circuit which should do the job.

[nctnico]

Thanks  I never knew those LED based CCFL replacements existed!

[plesa]

  Upgrade!!

[Howardlong]

Very impressive!

I did the Newscope LCD mod to my 8753A some months ago, it's taken two decades off it. Of course there's no VGA output on the 8753A, they have an FPGA to do the CRT untangling.

[TheSteve]

Here's a constant current LED circuit which should do the job.

Thanks for the schematic. I was pondering using a single supply opamp driving a pass transistor last night which would have been easy to make vary the voltage from 8 to 12 volts going into the existing 20 ohm resistor. I thought I would bread board your schematic though and it worked fine so I went with it. The BC237 was swapped for a 2N3906 and the two BC337's were replaced with a single TIP31C and a small heatsink I ripped off an old eprom programmer. I used the 4.7K resistor during testing but after installing it I wanted a little more drive current so I paralleled a 5.1K with it. This gives me adjustable drive current from 40 to 220 mAh. The new board is mounted in the original metal box I added, everything is working great. There was a small delay during final assembly when some hardware went missing. It was in a small plastic film container. It seems "Hunky Bill" thought it made a great toy as it rattled quite nicely when batted around. Attached are pics of the driver board, one showing it installed in the metal box, a shot of the LCD with the front panel removed and a picture of Hunky Bill in his "rest state" after taking a round out of any and all equipment in the shop.

I think it is finally time to stop taking the 8714C apart and put it to work!

[AF6LJ]

That's really great, looks good.

[andy2000]

I just picked up an 8711C which I've turned it into an 8712C with all the software options.  I found that writing 00 for the four option bytes turned it into an 8730A tuner analyzer.  I had to use 8B as found on this page:

https://translate.google.com/translate?hl=en&sl=cs&u=http://minolta1.cninet.cz/HP8712C/&prev=search

Next I'm going to try to use the digital LCD interface.  It looks like a standard 4 bit parallel output which should work with many LCDs.  The LCD gets its data from the same source as the DAC for the VGA output, so assuming there's no issue with timing, I think it should work. 

Keysight was nice enough to post schematics for the 871XC:

http://na.support.keysight.com/871x/schematics/

[andy2000]

I finally go around to adding the digital LCD interface.  It all went smoothly and worked the first time.  I just need to remove the CRT and mount the LCD.  I used a Mitsubishi AA084VC03 LCD panel.  I'll post some more detailed pictures soon. 

[R005T3r]

Nice upgrade! 

I'm very interested in these mods, maybe I can try to upgrade my old HP5402A with an LCD panel. The thing is, if something goes wrong I don't have any other scope...

[AF6LJ]

This is very Cool, looking forward to more pictures and info.
 

[TheSteve]

Yes, more info would be great. A cheaper and easier mod is anyways welcomed. It would be nice to ditch the VGA interface.

[andy2000]

Here are some more pictures of the project.  I'll post a list of part numbers for the ICs soon.  They were standard parts from Mouser.  I already had miscellaneous parts like caps and resistors on hand. 

U1025 is used for brightness control, but I didn't install it since I assume the firmware lacks support for that feature. 

I simply grounded the unused LSBs of the LCD. 

I mounted the LCD to a piece of Plexiglas which I attached to the CRT brackets on standoffs.  I used a router table to shave off the CRT bezel.

[andy2000]

Here's a list of the part number I ordered. 

U1008 -- LX8385B-33CDD -- 3.3v regulator
Q1001 -- FDS6679 -- P channel MOSFET
R1025 -- SOMC160333R0GEA  -- resistor array, 33 ohms
R1026 -- SOMC160333R0GEA  -- resistor array, 33 ohms
U1012 -- SN74LVT125D
U1009 -- SN74LS123DR
U1010 -- 74LVT574WMX
U1011 -- 74LVT574WMX
J1020 --  A3E-50PA-2DSA(71)

[KrudyZ]

I recently bought a nice copy of the HP 8714ET and have just received my LCD from Shenzhen.
https://www.ebay.com/itm/VGA-LCD-Controller-Board-RT2270C-With-8-4-AA084VC03-640x480-LCD-Screen/181965840286?hash=item2a5e025f9e:g:1oUAAOSwbtVZV2uh
I paid $90 shipped. It arrived within 10 days and was well packaged, so I had a good experience with this seller.
I chose to go the analog VGA route as it seems to require fewer modifications to the analyzer.
Here is a picture of the LCD kit plugged into the external VGA port and powered from a 12 V lab supply (it draws about 1 A).
This is using two fluorescent backlights. I'm still waiting on the LED strips to come in to update the backlight and complete the mod.
Rudy

[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.