UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Computers

Notices

Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

Closed Thread
 
Thread Tools
Old 11th Jan 2017, 3:31 am   #1
Argus25
Hexode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 322
Default Running 15.75kHz VDU's at 21.85Khz

This article might be of some interest to vintage computer enthusiast members.

It explains how the common vintage IBM 5153 colour computer monitor from the 1980's can be modified to auto detect EGA and increase its horizontal scan rate and display 16 colour EGA images:

http://worldphaco.com/uploads/INCREA...OR_TO_AUTO.pdf
Argus25 is offline  
Old 11th Jan 2017, 12:12 pm   #2
dragonser
Hexode
 
dragonser's Avatar
 
Join Date: Aug 2009
Location: Carshalton, Surrey, UK.
Posts: 281
Default Re: Running 15.75kHz VDU's at 21.85Khz

Hi,
yes this is useful. I did manage to damage a cub microvitec monitor trying to get it to work at a higher line frequency. Some arcade game boards have a non standard video output ( was medium resolution 24 khz ? )
regards Peter B
dragonser is offline  
Old 11th Jan 2017, 2:28 pm   #3
Argus25
Hexode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 322
Default Re: Running 15.75kHz VDU's at 21.85Khz

Quote:
Originally Posted by dragonser View Post
I did manage to damage a cub microvitec monitor trying to get it to work at a higher line frequency.
This is why in the modification to the IBM 5153 monitor the zener array is added to prevent failure of the horizontal output transistor. It is an interesting balance of factors. If the tuning capacitance on the line output transformer is dropped in value to allow the shorter flyback time for EGA, the peak voltage on the H output transistor collector increases.This is offset to some extent with reduced width which occurs when the H rate is increased anyway, but it still needs the additional zener array as outlined in the article. Also as noted there, IBM got away with it well in the 5154 monitor, because they separated the EHT generation from the H scanning system.
Argus25 is offline  
Closed Thread

Thread Tools



All times are GMT. The time now is 12:07 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright ©2002 - 2017, Paul Stenning.