Post Reply 
HP 82985A video interface for the Portable Plus - poor image quality
02-14-2020, 11:03 PM
Post: #1
HP 82985A video interface for the Portable Plus - poor image quality
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.
Find all posts by this user
Quote this message in a reply
02-15-2020, 12:57 AM
Post: #2
RE: HP 82985A video interface for the Portable Plus - poor image quality
Hi Michael,

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

[Image: Back.JPG]

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
Find all posts by this user
Quote this message in a reply
02-15-2020, 02:18 AM
Post: #3
RE: HP 82985A video interface for the Portable Plus - poor image quality
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.
Find all posts by this user
Quote this message in a reply
02-15-2020, 03:39 PM
Post: #4
RE: HP 82985A video interface for the Portable Plus - poor image quality
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
Find all posts by this user
Quote this message in a reply
02-15-2020, 08:33 PM
Post: #5
RE: HP 82985A video interface for the Portable Plus - poor image quality
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.
Find all posts by this user
Quote this message in a reply
02-16-2020, 05:24 PM
Post: #6
RE: HP 82985A video interface for the Portable Plus - poor image quality
I'm curious as to how bad is the display. Could you post some pics of the screen.

Dave
Find all posts by this user
Quote this message in a reply
Yesterday, 12:25 AM
Post: #7
RE: HP 82985A video interface for the Portable Plus - poor image quality
(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:        
Find all posts by this user
Quote this message in a reply
Post Reply 




User(s) browsing this thread: 1 Guest(s)