Author Topic: HP 8594E Replacing the green CRT with LCD  (Read 4024 times)

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Offline Miti

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #25 on: July 14, 2018, 07:43:04 pm »
One may be the caps failing a it takes a while to actually display anything on the CRT plus the whole image starts very large & unfocussed before settling down to a nice sharp & bright image.

The other is a dead CRT unfortunately. Thanks for the suggestion.

Phil

Yes, that is typical  dry caps symptom. You replace them with some good quality caps and you  give it another 10+ years.
That big spark at power up was by design!
 

Offline Miti

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #26 on: July 14, 2018, 07:44:58 pm »
I'm having a similar issue with an LCD monitor on the composite video output of my Anritsu MS-420K. The image on the LCD is shifted up and to the right, clipping off the top line of the display. The Super Circuits LCD measures 5.6" diagonal. Sadly, its menu has no adjustments for size or position.

I've emailed several sellers of LCD panel+controller combos on eBay, asking if their unit offered those adjustments. They all said no.

What about the instrument itself. Does it have horizontal and vertical adjustments like HP8590E series have?
That big spark at power up was by design!
 

Offline precaud

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #27 on: July 14, 2018, 08:53:49 pm »
It has them, but unfortunately they don't affect the external composite output, only the internal.
 

Offline Miti

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #28 on: December 04, 2019, 02:04:17 am »
I want to revive this topic. I think I found a reasonable solution from the cost and complexity perspective.
After I saw the Simmconn Lab's board (manual attached), I wanted colour. I wanted to find a simple solution to have a green graticule and yellow trace.
I know that my 5" AV LCD can synchronise when HP8591E is set to PAL video. I tried to separate the low and high brightness of HP8591 and feed them to green and red of an AD722 encoder, then feed the output CVBS to the LCD. The image is fuzzy and has relatively low resolution while there's colour crawling across the screen that is unacceptable. Screen shot attached.
Then I came back to directly driving the LCD from the SA video, I reduced the half brightness of the A16 video output by adding a 390 Ohm resistor in parallel with R301, as described in the same attached manual.
I then raised the output black level by about 250mV to make room for the sync pulses and added two transistors for HS and VS.
The result is shown in the attached simulation file, just rename the txt to asc.
Everything on the left of R13 is on the A16 board. R13 and everything on the right is my circuit.
The result is a B&W, very sharp image, with two levels.
Pictures and pros and cons in the next post.
That big spark at power up was by design!
 

Offline Quarlo Klobrigney

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #29 on: December 04, 2019, 02:15:40 am »
What kind of lead length do you have running from one area to another? Do you have a photo of the overview of the connections? The text file is wire here and there. Is that supposed to be a schematic layout? One more thing is there any coaxial running in there or are you doing plain wire. Plain wire is leaky. Coaxial is lossy and needs a DA.
Voltage does not flow, nor does it go.
 

Offline Miti

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #30 on: December 04, 2019, 02:20:46 am »
Here are some pictures with the result.

Pros:
* Cheap, the LCD can be bought on ebay for less than $50 and the rest is peanuts
* Not very invasive, you only add a resistor to the A16 board, everything else is external
* We have a solution to recover a SA with a dead display. A solution that costs 350 USD, is hard to justify for me.

Cons:
* No colour or at least green colour (even though it may be a solution. Modify the LCD driver to drive the green colour only, AKA shorting R and B lines to GND)
* Does not align perfectly to the plastic frame. The image fills the screen horizontally but it's a bit compressed vertically.
* No dimensional control. 5" is a bit small, 5.6"would fit better vertically but would go out of the frame horizontally, by my calculation.
« Last Edit: December 04, 2019, 02:32:36 am by Miti »
That big spark at power up was by design!
 

Offline Miti

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #31 on: December 04, 2019, 02:24:08 am »
And a picture with the frame and smoky screen.
That big spark at power up was by design!
 

Offline Miti

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #32 on: December 04, 2019, 02:27:14 am »
The text file is wire here and there. Is that supposed to be a schematic layout?

It is an LTSpice .asc file. Change the extension to .asc and open it in LTSpice.
That big spark at power up was by design!
 

Offline Quarlo Klobrigney

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #33 on: December 04, 2019, 03:25:14 am »
I thought this was with something that you were cobbling together that resulted in lack of high frequencies. I am confused.

Don't have LT Spice.
Voltage does not flow, nor does it go.
 

Offline Miti

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #34 on: December 04, 2019, 05:11:06 pm »
Don't have LT Spice.

It’s free software, very useful. You can download it.
Or I can take a screenshot and post it later.

Edit: Added schematic screenshot.
« Last Edit: December 04, 2019, 11:36:52 pm by Miti »
That big spark at power up was by design!
 

Offline Quarlo Klobrigney

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #35 on: December 04, 2019, 07:17:06 pm »
As long as they don't need a lot of info and my first born!
Voltage does not flow, nor does it go.
 

Offline madao

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Offline Miti

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Re: HP 8594E Replacing the green CRT with LCD
« Reply #37 on: December 05, 2019, 11:27:12 am »
What is typ of display ?

Here ?
https://www.ebay.de/itm/New-5-6-5-6inch-640-480-TFT-LCD-VGA-RGB-AV-Module-Display/121194129870?hash=item1c37bba9ce:g:sFgAAOxyWt5SW1Sm

There’s a link to the one that I bought in ones of my previous posts. As I said, 5.6” may go out of the frame horizontally.
That big spark at power up was by design!
 


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