How to see if a chip is for PAL or NTSC? VDP TMS9929AN / TMS9918AN NTSC/PAL 50Hz/60Hz ?

[globeron]

The issue:

I used my TMS9928A (?) Chip of my European TI-99/4A in my European TI-99/4 computer to fix the VDP

so these chips run on 50Hz and have the PAL Output  (and the RGB / YPbPr).

 

I ordered Chips from eBay (China ?)

* TMS9918AN - https://www.ebay.com/itm/1PCS-TMS9918ANL-Video-Display-Processor-DIP40/320857330410

* TMS9929AN - https://www.ebay.com/itm/320853018123?ViewItem=&item=320853018123

 

Result on my European TI-99/4A - white stripes on the screen (looks like sync. issue).

but I just tested in my USA TI-99/4A version (NTSC / 60 Hz) and got the TMS9918AN working okay (colours, etc.)

but the 9929AN only outputs in Black and White (for the rest it is okay).

 

Questions:

1. What is the reason for the Black & White output?   Bad Chip?  (cannot be the crystal as it works with 9918AN -

     or something else Frequency 50Hz/60Hz? 

 

2.  How can I identify a TMS99xx chip that supports PAL 50 Hz output for my European console ?

     (I asked already someone in Europe I send a lot of broken consoles to, to see if he has a spare TMS99xx chip for me)

 

This table is a bit confusing, then the 9929A should not output Composite signal ?

(https://en.wikipedia.org/wiki/Texas_Instruments_TMS9918)

 

Also I look around to figure out what the 9929 chip is:

* 

 

 

 

 

 

First I thought it are fake chips I have to deal with.

 

Detecting Fake chips:

 

 

 

[globeron]

TI-99/4A USA console with composite cable output.

 

TMS9929AN  outputs in Black and White

 

TMS9918AN outputs in Colour

 

 

[Stuart]

The 9918 outputs colour composite on a single pin. The 9928/29 outputs video on three pins - luminance (the 'black and white') on one, and colour difference on the other two - and these are combined into a single colour video signal in the (external) PAL UHF modulator. There are some links on the board that you set according to the VDP in use. So with a 9929 plugged into a board set up for a 9918, you're only getting the luminance signal, with no colour information.

Edited January 7 by Stuart

[globeron]

11 hours ago, Stuart said:

The 9918 outputs colour composite on a single pin. The 9928/29 outputs video on three pins - luminance (the 'black and white') on one, and colour difference on the other two - and these are combined into a single colour video signal in the (external) PAL UHF modulator. There are some links on the board that you set according to the VDP in use. So with a 9929 plugged into a board set up for a 9918, you're only getting the luminance signal, with no colour information.

Thank you!  So the reason 9929 does not work in a PAL European version of the TI is the frequency 60Hz ?  

[Asmusr]

2 hours ago, globeron said:

Thank you!  So the reason 9929 does not work in a PAL European version of the TI is the frequency 60Hz ?  

No, it *should* work. A PAL EU TI-99/4A needs a 9929A (50 Hz) and a NTSC US TI-99/4A needs a 9918A (60 Hz). The 9928A is not used.

[globeron]

4 hours ago, Asmusr said:

No, it *should* work. A PAL EU TI-99/4A needs a 9929A (50 Hz) and a NTSC US TI-99/4A needs a 9918A (60 Hz). The 9928A is not used.

Thank you, maybe something wrong with the chip maybe not a 9929, because in the PAL system it does not give any result. 

[ChildOfCv]

As Asmusr noted, you have to change some jumpers on the PCB if you change between 9918 and 9929.  The PAL version was made to output to SCART, if I recall correctly, and will not give you color on the tuner output.  That requires extra hardware to modulate the colors at a certain frequency (which is different between PAL and NTSC) and then combine it with the B/W signal.  That composite signal then goes through the tuner box which also adds in the sound (at another frequency which is different between NTSC and PAL).

So if you have an NTSC unit, you can convert it to PAL, but you will not be able to just drop in the 9929 chip.  You'll have to change jumpers, and even then you'll have to use SCART.

[JB]

Given it apparently works at 60 Hz but not at 50 Hz... it seems likely your 9929 is actually a 9928.

[zxMarce]

Please take the following with a grain of salt; I did not check the TI's schematic; I'm talking video in general, as a TV repairman in the '80s would.

 

Actually, there's more to video than just 50/60 and RGB - Composite - YPbPr...

In the race for Colour TV, several standards were developed (we're talking post WWII here). We'll focus on NTSC (USA, Japan, etc) and PAL (most of Europe, France being an exception with SECAM).

 

To encode chrominance (chroma, or just colour) on the luminance (luma, luma+sync, brightness, or just Y) signal, a subcarrier is added and the chroma signal is sent as a phase-modulation of this subcarrier "on top". The luma (Y) signal alone comprises "ye olde" brightness and horizontal/vertical sync signals originally sent to B/W only TVs. Incidentally, this is why most of the time something is not right, you just get B/W: Luma+Sync (Y) is the foundation of TV broadcast. Colour comes... "afterwards".

 

NTSC (strictly speaking NTSC-N) uses a subcarrier of 3.579545 MHz (3.58 for short) while European PAL (PAL-B) uses 4.43361875 MHz (4.43 for short). This is a most important bit to know.

 

The various TMS99x8 chips encode the video differently, and the composite (NTSC, TMS9918) should be sent modulating a 3.59MHz, while the luma and chroma-difference signals (PAL, TMS9929) should modulate 4.43MHz. Any mixup will result in B/W display because the TV cannot lock its internal chroma oscillator to the input signal. And some noise may be seen in the B/W picture as the chroma subcarrier would not be filtered (dot-crawl is an example).

Also, PAL will phase-invert the RED component every scan line to fix -and make redundant- NTSC's hue shift (and its knob).

Again, this is for the dated CRT TVs available back in the day - With modern equipment, it is actually up to the TV model to say if the signal is "acceptable" or not. That is also why "some" modern TVs work and "some others" do not.

 

To add problems to trouble, the NTSC chip TMS9918 uses a single pin to spit out just composite, while the PAL devices TMS9928/9 use three pins, one for luma (Y) and two for chroma-difference (Pb, Pr) signals.

Regarding TI-99/4A modulators, the NTSC ones would just mix audio and composite, and amplitude-modulate the TV channel RF signal. An easy task.

While PAL modulators had to work harder by creating composite out of Y-Pb-Pr, and mounting it on the TV channel RF signal. That's where the LM1889N entered the stage to do the heavy-lifting.

 

All in all, I guess that if you just swap chips you will not have a proper picture. At a minimum, I'd say the chroma crystal may need to be changed. Also if you're going NTSC->PAL you need to route the difference signals Pb and Pr to the output.

 

Hope that sheds some light,

zxMarce.

Edited February 6 by zxMarce

[ChildOfCv]

On 2/6/2021 at 2:39 PM, zxMarce said:

All in all, I guess that if you just swap chips you will not have a proper picture. At a minimum, I'd say the chroma crystal may need to be changed. Also if you're going NTSC->PAL you need to route the difference signals Pb and Pr to the output.

It's not quite as hard as you think though, because the modulator is actually an external attachment.  For NTSC, the 9918 will send a composite signal to the video output plug.  For PAL, the 9929 sends YPbPr to the video output plug.  So if you have SCART, you just need an adaptor for the video plug.  A 9928 could also be substituted for YPbPr with NTSC timing.

[globeron]

Thank you all, very useful information!