Apple ][+ clone PAL to NTSC modification?

5 posts / 0 new
Last post
Offline
Last seen: 2 months 2 weeks ago
Joined: Dec 6 2016 - 05:55
Posts: 10
Apple ][+ clone PAL to NTSC modification?
AttachmentSize
Image icon Unitron_triangular_pads.JPG897.31 KB

Hi all,
I recently came into possession of a Unitron U2000 Apple II+ clone, partially modified for PAL video output. Of the various screens I've tried only my Samsung TV can successfully lock onto its monochrome signal, and then only after careful tweaking of the video pots on the motherboard.

IMAGE(https://s17.postimg.org/snj6g0om7/Samsung_Unitron_video.jpg)

IMAGE(https://s17.postimg.org/ue27hi65b/Unitron_slot_assignment.jpg)

(White balance of the Samsung was set to all-green in the second photo)

Picture is reasonably stable but you do sometimes get these abrupt horizontal shifts to the left, lasting a few seconds before it rights itself.

Anyway, I would like to revert this unit to NTSC for colour and greater picture stability.

IMAGE(https://s17.postimg.org/5ncj3oqsf/Unitron_triangular_pads.jpg)

As you can see the triangles at A and B have been cut on the motherboard.
I suppose they need to be rejoined. (Sorry for the bad photos but A and B are the only places where cuts were made)

But what about the solder blobs at C, D, and E? Should they all be removed?

Helpful page showing the correct modifications to a Europlus for NTSC - http://www.8bit-homecomputermuseum.at/repair/apple%20ii%20europlus%20color%20mod/apple_ii_europlus_color_mod.html

So I'm assuming the Unitron follows a similar pattern.

The motherboard has a 14.318MHz crystal, already correct for NTSC, so no change necessary -

IMAGE(https://s17.postimg.org/aan6j73j3/Unitron_crystal.jpg)

Before I touch anything, any insight or tips from forum members will be greatly appreciated!
Thanks...

speedyG's picture
Offline
Last seen: 4 years 9 months ago
Joined: Nov 16 2011 - 07:45
Posts: 2493
Re: Apple ][+ clone PAL to NTSC modification?

At least at original board either X-pads or O-pads are open.
If you close X-pads then you must remove solder from O-pads and
take care that halfcircles are disconnected.

Offline
Last seen: 2 months 2 weeks ago
Joined: Dec 6 2016 - 05:55
Posts: 10
Re: Apple ][+ clone PAL to NTSC modification?

Thanks for the advice! Solder pads were successfully reverted and getting great colour now:-

IMAGE(http://www.applefritter.com/files/Unitron_pads_reverted_to_NTSC.JPG)

IMAGE(https://s28.postimg.org/uktwmzbf1/Taxman_NTSC_colour_Unitron_Samsung_TV.jpg)

IMAGE(https://s28.postimg.org/aeqeo3frh/Taxman_NTSC_colour_Unitron_Samsung_TV_2.jpg)

IMAGE(https://s28.postimg.org/5imrwefm5/Taxman_NTSC_colour_Unitron_Samsung_TV_3.jpg)

speedyG's picture
Offline
Last seen: 4 years 9 months ago
Joined: Nov 16 2011 - 07:45
Posts: 2493
Re: Apple ][+ clone PAL to NTSC modification?

Hello ben 23239,

at this point there are probably 2 more options to optimize the colors...
1: at modern TV's the setup often offers advanced options in the setup screen.
In such case then there are options availiable about selecting between NTSC, SECAM and different kinds of PAL
( by country or by normativ name ) .... in such case it's recommended to select either Germany or PAL (BG)
2: by very careful adjustment of the color trim at the mainboard.

happy holidays
speedyG

Offline
Last seen: 2 months 2 weeks ago
Joined: Dec 6 2016 - 05:55
Posts: 10
Re: Apple ][+ clone PAL to NTSC modification?

Hi speedyG, wishing you a merry Xmas!
I had some trouble getting a stable, centred picture in colour and was forced to play around with the pots. There are three in total on this board - two in the upper right, one on the lower left. All have an effect on the picture (monochrome/colour, colour correctness, and image stability). After several hours, trying different software, I think I have it tweaked as good as can be now. At least the picture is horizontally centred for both text and graphics - the colour trim adjustment definitely helped here. Vertically there is occasional judder but mostly okay. Also with this Samsung the S-Video gives better image (using a short RCA to S-Video cable). But even then, the contrast varies according to how much appears on screen... the background only goes fully black when screen is filled up.
I'm sure it depends a lot on the make and model of TV - composite inputs may have been added more as an afterthought with this one.

Log in or register to post comments