HP 82985A video interface for the Portable Plus - poor image quality

[Michael Fehlhammer]

A relatively rare accessory for the HP portable plus was the video interface that enabled power users to enjoy better image quality compared to the early ( non back lit) LCD. The monitors usually attached to the interface where the 82912A and 82913A, which also were the standard monitors for the HP 86 and the calculator video interfaces (HP-IL, 82163A, mountain computer ...).
Now I have got two of these interfaces and two portable plus computers that came with the necessary connector ( built into the battery door).
But when I look at the screen I can't understand why anyone should prefer THAT picture to the standard LCD...
The problem is inverse video: The DOS shell (PAM) makes excessive use of it, to mark key assignments (menu selections). The labels are hard to read, sometimes completely illegible.
Now I swapped interfaces, computers, monitors ... the result remained the same.
Next step was that a colleague replaced the usual suspects (electrolytic capacitors, f.e.), especially in a module denoted "sync mixer" which I assumed might be responsible for the mushy picture.
No success unfortunately, not even a slightly better image quality.
My colleague guesses that the image processor named "ILA -T08834" (can be found on the schematics created by Tony Duell) could be responsible and should be replaced next. But where to find such a very special IC? Any other ideas?
Does anyone have experienced the same problems with that video interface?

By the way, we found one strange difference between the schematics and the actual installed components: One capacitor in the "sync mixer" module actually is 200pF, instead of 10 pF in the schematics. Both my video interfaces (rev. A and A-4) have the 200 pF capacitor. The schematics are for the rev. A.

[Dave Frederickson]

Hi Michael,

My Portable PLUS prototype has the necessary interface connector, but I've been unable to find an interface.



Several years ago I was helping a member research the cable connectors.
https://www.hpmuseum.org/forum/thread-41...38420.html

So, an interesting problem you have.

If you'd like to lend me one of your interfaces and cable I'll investigate the issue. I have a 82912A monitor which I find works better with the vintage video interfaces.

Dave

[Michael Fehlhammer]

Hello Dave,
interesting hint about the monitors, I will connect the smaller monitor and see if it makes a difference.
Of course I can lend you interface & cable, thank you for the offer to investigate the issue.
I found the two older threads about the video interface, there hasn't been much attention to it from the community; it seems to be a very rare device, despite the popularity of the portable plus.
By the way, since I know that you are a great PP expert:
Did the legendary third party 4 MB Ram drawer ( IIRC it was mentioned in an ad in the Portable Papers) appear anywhere? I mean, is there a single known existing sample today?
It would be so great if a skilled electronics expert nowadays could start a RAM disk extension project for the PP ... it deserves more memory. HP-IB HD drives, connected via HP-IL/IB interface, are ridiculously slow.

[Dave Frederickson]

Hi Michael. Regarding the monitors, what I meant is that the older monitors seem to have a lower input bandwidth and do not exhibit the high frequency noise noticeable with newer monitors.

The 4 Mb RAM Drawer I believe appeared in the Portable Paper however a quick check only turned up the 1 Mb drawer.

Note: Since the entire Portable Paper is present in OCR form on the HP Computer Museum website you can perform a Google search using something like "4 Mb RAM site:hpmuseum.net".

Until someone designs a RAM disk, have you tried some of the data compression utilities for the PP like Squish Plus?

Dave

[Michael Fehlhammer]

well, data compression (Squish Plus) is a good idea, I read about it and then forgot again.
I guess when using compression, one could typically about double the effective space. Still relatively small electronic disc memory, but of course much better than 1MB.
On Portable Paper, issue July/August 1990, pages 25/26, I found a discussion of planned(!) memory extensions for the Portable Plus, among them a 20 MB hard disk drive in a memory drawer, and enhanced RAM drawers with up to 8 MB.
For a 2MB version, the editor of the magazine had received quotes already. He thought that the selling price could be around $ 1500.-, which would have meant 50% more than the price for the standard 1MB HP RAM drawer at that time.

It seems that these projects never went beyond the prototype state.

[Dave Frederickson]

I'm curious as to how bad is the display. Could you post some pics of the screen.

Dave

[Tialuna]

(02-16-2020 05:24 PM)Dave Frederickson Wrote:  I'm curious as to how bad is the display. Could you post some pics of the screen.

Dave

Hi there, I am Mr. Fehlhammers compagnion and here are the pictures of the poor image quality. I hope it helps a little bit:        

[Klaus Overhage]

   
This picture shows my old 19 inch Belina VGA monitor connected to an Extron DVS 304. I read about it in the thread HP-75C Demo and can confirm it produces a very clear, steady image.

[Martin Hepperle]

(08-16-2022 07:21 AM)Klaus Overhage Wrote:  This picture shows my old 19 inch Belina VGA monitor connected to an Extron DVS 304. I read about it in the thread HP-75C Demo and can confirm it produces a very clear, steady image.

I also have this interface and am very happy with it. I am using it with a small TFT panel and the picture is much, much better than the built-in LCD screen. Especially if you compare with the early gray LCD. But also compared with the green LCD variant it is much better.
There are some glitches (uneven character stem widths) due to scaling/aliasing to the TFT resolution, but this is expected.
The inverse video parts indeed "bleed" a bit, but if you really work with the Portable, you will not do much in PAM.
I have written a few Turbo Pascal programs using this video interface and find it very useable.
If you use the NEC/HP green monitor, you might want to reduce brightness, this might also help to obtain a better image with less bleeding.

It might be an interesting project to build a new interface for this purpose but one has to sample the digital LCD output at a relatively high rate so that one would probably have to revert to a FPGA or similar device. Such a new interface could be designed to better match the resolution of modern TFT screens and avoid generating analog output.

Martin

[Roland57]

(02-26-2020 12:25 AM)Tialuna Wrote:  Hi there, I am Mr. Fehlhammers compagnion and here are the pictures of the poor image quality. I hope it helps a little bit:

In my opinion the settings for brightness and contrast are set wrong: for a CRT monitor...

1) set both controls to their minimum.
2) Then increase both simultaneously unless you see a picture.
3) Then adjust brightness to an accepable level of white, but as low as possible.
4) With the contrast control set dark regions to real black.
5) repeat the last two steps if neccessary, important is to keep in mind that brightness is for white parts of the picture and contrast for the black ones.

Roland

[Michael Fehlhammer]

Hi Roland,

thank you for your hints!
Our contribution to this thread is old and outdated, meanwhile we are happy with the picture quality of our PP - 82985a - 82913a combo.

Best regards!

[Roland57]

(08-26-2022 01:37 PM)Michael Fehlhammer Wrote:  Hi Roland,

thank you for your hints!
Our contribution to this thread is old and outdated, meanwhile we are happy with the picture quality of our PP - 82985a - 82913a combo.

Best regards!

Hi Michael,

how have you solved your problem ? It could be helpful for others having the same problem,

best regards
Roland

[Dave Frederickson]

(08-26-2022 04:47 PM)Roland57 Wrote:  how have you solved your problem ? It could be helpful for others having the same problem,

Michael's issue was solved by setting the impedance switch on the back of the monitor to 75 OHMS.

[Roland57]

(08-28-2022 01:22 AM)Dave Frederickson Wrote:  

(08-26-2022 04:47 PM)Roland57 Wrote:  how have you solved your problem ? It could be helpful for others having the same problem,

Michael's issue was solved by setting the impedance switch on the back of the monitor to 75 OHMS.

thankyou !

regards
Roland

[Michael Fehlhammer]

Hi Roland,
Dave is right. Apart from changing the impedance setting of the monitor, on the video interface board we replaced two ceramic capacitors (10 nF and 10 pF, according to Tony Duell's schematics).