VGA Monitor for a HP-86B ???


J K
 

I just recently joined this group after I finally got myself a HP-86B after 40 years of thinking about it. 

I was hoping I can connect the HP-86B to an old VGA LCD screen, based on what I read on hpmuseum.net " If you don't have a composite monitor of any kind, you can use your HP-86 with a standard VGA monitor. To do this, you will need a composite-to-VGA converter box (which cost about $20)." But it does not seem to be that straight forward, I do get a picture but the characters seem to be double lined in vertical direction and the beginning of each line seems to be outside of the screen, a few characters are missing. I wonder how others have solved this, am I using the wrong video to VGA converter, the wrong type of VGA monitor or is the HP-86B faulty. Or is that behaviour just normal ?

I would really appreciate someones perspective here. I know there was a similar thread a few years ago but I am not clear if this was ever brought to closure.

Thanks for your help, I really hope someone can give an answer. 

Joerg


Mark Bielman
 

Joerg,

I repaired these guys @ hp and have had the 85 (A/B) for years. Love it!
Recently acquired an 86B... had the exact problem. Never figured it out.
Suspect that HP had those (86x) monitors altered to work properly.
Standard NTSC monitors are not so good.

Mark


Mark Bielman
 

So to better answer your question, that is normal behavior with your approach.
It's normal for the 86.

Mark


Ash
 
Edited

I have HP-86B and it used to work on an old IBM PC mono monitor, to far back to remember if I had to adjust monitor sync, but I would have expected it to work with some minor mods??
Double or smearing of data would be bandwidth issue you may need a monitor with underscan mode option.
Some people have had success using RCA to PC VGA converters.
Specs for the HP86B output are on page 54 of the "Introduction to the HP-86B" manual, if you need a copy let me know or you can download manual online.

Update: this may help you if you can find one, although his TV underscan may be why it worked for him http://www.vcfed.org/forum/archive/index.php/t-30959.html
Something like this may work if it handles the off standard composite in https://www.amazon.co.uk/MakeTheOne-Composite-Converter-Computer-Projector-S-Video-AV-VGA/dp/B081SBNJ58/ref=pd_lpo_147_t_2/261-0241049-3105273?_encoding=UTF8&pd_rd_i=B081SBNJ58&pd_rd_r=f6e5a133-7c49-44b7-8194-66f77ce6dc47&pd_rd_w=gpHY8&pd_rd_wg=NBOAs&pf_rd_p=7b8e3b03-1439-4489-abd4-4a138cf4eca6&pf_rd_r=TT882RABBJ4JK85W1ZYC&psc=1&refRID=TT882RABBJ4JK85W1ZYC

Ash


Paul Berger
 

I use an ordinary Zenith green screen monitor with mine, but you are right the sync signals are far enough off NTSC to cause a lot of monitors to not work, the monitor has to have a extra wide range of sync before it will work.  According to the Intro to 86B Manual the horizontal sync frequency is about 100Hz slower than a standard North American B&W TV signal.  It would seem that the video timing is derived  from the system clock so tweaking it a bit might get the signal closer, however it would throw off other things like timers and clock.

I have heard of some people having success with composite to VGA adapters, but it would need to have a wide capture range.  I have tried two different ones and have not had any success.

Paul.

On 2020-08-20 10:10 p.m., Mark Bielman wrote:
Joerg,

I repaired these guys @ hp and have had the 85 (A/B) for years. Love it!
Recently acquired an 86B... had the exact problem. Never figured it out.
Suspect that HP had those (86x) monitors altered to work properly.
Standard NTSC monitors are not so good.

Mark


J K
 

Just wanted to say thank you for all your responses.

I am intrigued by the idea to slightly vary the clock frequency, that should be pretty easy to do, just replace the TTL oscillator signal with a TTL signal from a pulse generator. If that works, I think the clock would not be off by too much, it's just 0.5% of the 15.73 kHz base frequency if I understand that right. I think I will do it just for the fun of it.
I also ordered some NTSC to VGA converters to try - it seems this is a hit or miss business. Connecting an old LCD screen is really what I would like to do.

Still wondering if there is anyone out there who actually has a working system using a RCA to VGA converter setup. 

Joerg


Ash
 

Maybe you could kindly let us know the details of the converters you have tried so others don’t try those in the future. I have contacted a manufacturer to find out if they have a product or solution ie modified converter that will work. Waiting on a reply.

regards,


J K
 

Oh, I certainly will. 
Joerg


J K
 

Just wanted to give a brief update as promised. Two of the converter arrived and I could not resist to try them. One is a dud - awfull picture - and has to go back, but the other one looks at least like a step in the right direction. It only displays 15 rows, I can live with that, but only 78 characters in the line, with the first and last missing. The first one missing bugs me. Any idea what is going on ?
I will summarize the results when I tested all the converters.


Paul Berger
 


On 2020-08-22 2:02 p.m., J K via groups.io wrote:
Just wanted to give a brief update as promised. Two of the converter arrived and I could not resist to try them. One is a dud - awfull picture - and has to go back, but the other one looks at least like a step in the right direction. It only displays 15 rows, I can live with that, but only 78 characters in the line, with the first and last missing. The first one missing bugs me. Any idea what is going on ?
I will summarize the results when I tested all the converters.

_._,_._,_


That is a much better result than I have been able to get , does the LCD monitor have any image adjustments?  The NEC monitor I use with my old computers allow for adjusting the position of the image as well as horizontal size.   In you picture it looks like the cursor is at the top of the screen, so maybe all 16 lines would fit.

Paul.


Mark Bielman
 

That's the best I could ever get as well.


J K
 

Yes, the monitor has some adjustments for positioning but it does not solve the issue. I found another resolution setting that gives me almost 16 lines now and 79 characters - unfortunately the first character is still missing.
I am not a video signal expert (maybe there is one out there reading this ?) but I have a suspicion the converter fails to capture the data for the first character in the line. Maybe the answer is then in the odd timing of the Hsync signal for the HP86B, it's not only the frequency is off, it's also that there are some odd timings in the blanking period, the time between the sync pulse and the first pixel in the line is off vs standard NTSC. No idea why HP could not just stick to the standard.

Any insights anyone ?

Joerg


J K
 

... and that would maybe be consistent with the fact Mark never got beyond this either.


Mark Bielman
 

As I recall, there are some one-shots in the sync generator circuits. Wonder if you added some pots in there for adjustments?

I have a prototype "desktop Integral" (project was killed) that uses an external monitor. The frequencies for that are quite odd.
Struggled for a long time with that one. Ended up finding a multi-sync monitor with all kinds of adjustments. That did the trick!

(NEC LCD 1800, Model LSA831W 17" Monitor)

Mark


Vassilis PREVELAKIS (series80.org)
 

Hi,

NOTE: I am in Europe so the scan rates of my European 86B may be different than the ones used by your US 86B.
But my converter also works with my US 9915A.

I guess I was lucky in that the first converter I tried from Amazon worked very well.
Here is the link (in case it helps) : https://www.amazon.de/gp/product/B01HHNXCTI

While this is a composite to HDMI converter, I also remember having good results with this type of adapter:
GBS8200 CGA/EGA/YUV/RGB to VGA Video Converter

https://www.amazon.de/Portabler-GBS8200-Channel-Converter-CRT-LCD-Monitor-gr%C3%BCn/dp/B00W3460UU

I am not at home at the moment but when I get back I'll send you pictures from the display.

Best Regards
**vp
www.series80.org


Paul Berger
 

I am not sure why the vertical would be off that should be straight forward as it is quoted a 59.9 Hz so only very slightly less.  Your monitor is likely expecting a vertical interval of  16.667 mS so at 59.9 Hz the vertical interval is going to be 27.824 uS longer.  The Horizontal frequency specified in the manual is  15.65 KHz.  There are two possible horizontal frequency for North American television, the original B&W specification was 15.75 KHz (63.49uS) but NTSC colour is slightly slower 15.734 KHz (63.56uS).  The specification for the 86 is 15.65KHz (63.9us).   The effect of the slightly longer horizontal and vertical intervals means that the 86's picture is going to be slightly higher and wider than a "normal" TV picture.

It may be that with the difference in signal timing the convertor may not be able to fit the the picture into a VGA frame.  Another possible source of a problem is how long the convertor waits after seeing the sync pulse before it starts looking for picture information.  In a TV signal the picture information does not immediately follow the horizontal sync signal.  The more I think about this it is more likely that you would need controls on the convertor to tweak how it fits the composite frame into a VGA frame rather than adjustments on the monitor.  The two old computers I use on my LCD monitor are HP 9000 300 series machines and I am using display adapter that have separate red, blue and green signals, specifically chosen to have signal timing very close to super VGA, the only issue I had was I needed a LCD monitor that could support SYNC on green.     

I had tried a couple composite to VGA adapters with my 86B with no success, but I cannot find them right now.

Paul.

On 2020-08-22 3:43 p.m., J K via groups.io wrote:
Yes, the monitor has some adjustments for positioning but it does not solve the issue. I found another resolution setting that gives me almost 16 lines now and 79 characters - unfortunately the first character is still missing.
I am not a video signal expert (maybe there is one out there reading this ?) but I have a suspicion the converter fails to capture the data for the first character in the line. Maybe the answer is then in the odd timing of the Hsync signal for the HP86B, it's not only the frequency is off, it's also that there are some odd timings in the blanking period, the time between the sync pulse and the first pixel in the line is off vs standard NTSC. No idea why HP could not just stick to the standard.

Any insights anyone ?

Joerg


J K
 

Mark, 
Thank you for that suggestion. Does that monitor have a vga or a rca/composite video input ? Like Paul, I actually think the issue is in the front end of the vga converter. Any character that does not make it through is lost. But I may be wrong.
Joerg


J K
 

Paul, I think I am with you. I could imagine the issue is the positioning of the Hsync pulse with respect to the first character in the line. Maybe the converter just puts it's window where it takes data in the wrong spot - and it may also be too short. The first issue may be solvable by playing with the positioning of the Hsync signal vs the image signal. The Hp86b schematic is pretty straight forward, Hsync, Hsync and image are all nicely separate before they are combined into the composite signal. Putting a triggered pulse generator with a delay and variable pulse width in the Hsync path should shine some light on this, would you agree?

I think ash has long gone down that path of thinking. Curious how his inquiry will turn out.

Joerg


Mark Bielman
 

It is VGA/RGB with sync-on-green option. I actually use a video distribution amp to drive all 3 (RGB) inputs to make it monochrome.
(hopefully the attachment worked!)

Mark


jeff.birt
 

FWIW, I have found that Extron video scalers do the best job for the money on a variety of vintage video sources. The IN1502 does a good job on the composite and SVideo sources I have tried. The DVS-304 (with VGA output, not DVI output) does a good job with composite, SVideo and RGB inputs.

 

Most of the testing I have done have been with NTSC sources. I know the DVS-304 does not do a good job with some PAL inputs, I have not tried the In1502 with PAL inputs though.

 

You can find these inexpensively on eBay if you’re in the USA.

 

Jeff Birt

 

From: hpseries80@groups.io <hpseries80@groups.io> On Behalf Of J K via groups.io
Sent: Saturday, August 22, 2020 6:58 PM
To: hpseries80@groups.io
Subject: Re: [hpseries80] VGA Monitor for a HP-86B ???

 

Paul, I think I am with you. I could imagine the issue is the positioning of the Hsync pulse with respect to the first character in the line. Maybe the converter just puts it's window where it takes data in the wrong spot - and it may also be too short. The first issue may be solvable by playing with the positioning of the Hsync signal vs the image signal. The Hp86b schematic is pretty straight forward, Hsync, Hsync and image are all nicely separate before they are combined into the composite signal. Putting a triggered pulse generator with a delay and variable pulse width in the Hsync path should shine some light on this, would you agree?

I think ash has long gone down that path of thinking. Curious how his inquiry will turn out.

Joerg