Hello all,

I have a beige TI99/4A and the TI RF modulator (MDP-VA3410) finally
failed[1]. My TV takes composite video so I decided to cut off the
modulator and convert to RCA plugs for composite video.

I used the modulator's circuit board labels to identify the audio, video,
and ground wires (and to avoid the 12V line). After soldering everything together I note that continuity testing produces a different pinout
compared with what I've read on various sites. According to <https://www.99er.net/TIvideoadapter.htm> I should have:

DIN pin Connection
------- ----------
1 Unused
2 Ground
3 Audio
4 Video
5 Unused


Instead, I find:

DIN pin Connection
------- ----------
1 Audio
2 Ground
3 Unused
4 Ground
5 Video

The cable seems to work fine, however. I get crisp video and audio. One
thing I wasn't sure about was the ground shield around the coaxial video
wire (bare and clear) in the RF modulator cable assembly. I tied this to
the black ground wire and the ground shields from the RCA plugs.

My understanding is that the beige TI99/4A was the last model produced.
Was the video pinout changed in these later models? This machine is second
(or third) -hand to me and I'm not aware of the repair/modification history.

Thank you,

Tom


1: Well, mostly...it produced an unusably unstable picture after a few
months of staticy video and audio; seems to be a problem with the antenna/modulation switch.

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No the Pinout is identical in all 4a models

https://www.arcadeshopper.com/wp/category/tifaq/ has the ntsc Pinout as pins 3 audio and 4 video and 2 ground. There's sometimes confusion on which side of the connector you are on so be careful.

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On 2020-08-12, Gregory McGill <arcadeshopper@gmail.com> wrote:

No the Pinout is identical in all 4a models

https://www.arcadeshopper.com/wp/category/tifaq/ has the ntsc Pinout as
pins 3 audio and 4 video and 2 ground. There's sometimes confusion on which side of the connector you are on so be careful.

Hi Gregory,

Thanks for confirming. I numbered the pins in my chart looking at the face
of the connector (the side which attaches to the TI). Even if reversed I
still shouldn't have the connections I have...I'll have to double check everything. Maybe the RF modulator labels are wrong. Here's a picture of
the board inside the RF modulator (just for fun): <https://www.canich.net/images/TI_MDP-VA3410.jpg>


Tom

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I have nice cables ready made in my store if you decide not to worry about that old cable I also always double-check the pin configuration with a continuity test in my multimeter before plugging it in.

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Tom,

I'm not sure about the pinouts. If you haven't already, you may want to step over to Atariage.com for the TI-99/4A group. There are a lot of hardware experts online over there that I am sure will step up right away and get you some answers if you do not get one from this group.

Beery

--Beery Miller -- 9640 News BBS -- 9640news.ddns.net:9640 --

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On Wednesday, August 12, 2020 at 5:00:14 PM UTC+2, Gregory McGill wrote:

No the Pinout is identical in all 4a models

https://www.arcadeshopper.com/wp/category/tifaq/ has the ntsc Pinout as pins 3 audio and 4 video and 2 ground. There's sometimes confusion on which side of the connector you are on so be careful.

Don't forget the 50Hz model with its 6-pin DIN, though. I thought OP may have been in Europe when he said he wasn't getting the right pinout.

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Weird that you got a different pinout. The only TI-99/4As that had different video pinouts were the 50Hz ones, so I thought you might have been in the UK or something.

Do you have a photo of your soldering at the 5-pin DIN?

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On 2020-08-16, Brian Tristam Williams <briantwcries@gmail.com> wrote:

On Wednesday, August 12, 2020 at 5:00:14 PM UTC+2, Gregory McGill wrote:

No the Pinout is identical in all 4a models

https://www.arcadeshopper.com/wp/category/tifaq/ has the ntsc Pinout as
pins 3 audio and 4 video and 2 ground. There's sometimes confusion on which >> side of the connector you are on so be careful. > > Don't forget the 50Hz >> model with its 6-pin DIN, though. I thought OP may have been in Europe when >> he said he wasn't getting the right pinout.

Thanks all for the responses. Hope you don't mind a summary reply.

Gregory: this cable seems to be working correctly, despite the odd pinout,
but I'll keep your store in mind.

Beery: Thanks, I've been trolling around atariage but haven't joined or
posted. I may do that.

Brian: I'm in the US with a 60 Hz model, 5 pins. I don't have pictures of
the DIN plug soldering as I reused the plug and wire from the RF modulator (just cut it off).

I think my next step is to crack the case and look for any modifications on
the motherboard. I can't imagine there are any, which just leaves me more confused as to why it works at all. I'll report back if I find anything unusual. The good news: no pins show 12V... :)

Thanks again,
Tom

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Thanks, Tom

Hope you don't mind, but I'm curious now. I thought you may have cut the cable, but then I wondered how you knew how it was wired up differently? How were you able to see which wire went to which pin? Or did you use a multimeter to check continuity?

Excuse my curiosity but I still have 8 lives left, so I should be good :-D I rate it as highly unlikely that any NTSC console would have a different pinout than the others - there wouldn't be any need for any such modification. (makes no difference
whether beige or black/silver)

Fact of interest, being in 50Hz land here: I have several 50Hz consoles and one NTSC console, and it turns out that the PCB tracks are no different for the video output stage for the 50Hz model. You can pull the TMS9929A and replace with a TMS9918A and
get your composite NTSC output (got some of them VDP chips from China). You can even pull the 6-pin DIN connector and replace it with a 5-pin - the board is made to accommodate them both. I'd like to do a YouTube video on that sometime.

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Hi Brian,

On 2020-08-17, Brian Tristam Williams <briantwcries@gmail.com> wrote:

Hope you don't mind, but I'm curious now. I thought you may have cut the cable, but then I wondered how you knew how it was wired up differently?
How were you able to see which wire went to which pin? Or did you use a multimeter to check continuity?

Not at all! I'm also quite curious. Here's what I did:

1. Open cover on RF modulator to document wire connections to circuit board there (see the image URL posted earlier in this thread). The board was
nicely labeled so I knew which color wire for audio (yellow), video (clear inner), and ground (black, plus bare shield from video).

2. Cut the cable about 8 inches back from the modulator case.

3. Cut about 12 inches from an old video/mono audio RCA cable set.

4. Stripped yellow, clear, and black wires from TI cable. Stripped inner cables from RCA cables.

5. Twisted the bare RCA shields together. Tinned everything.

6. Soldered bare RCA shields, TI bare video shield, and TI black ground together.

7. Soldered TI yellow to RCA audio wire (white connector).

8. Soldered TI clear to RCA video wire (yellow connector).

9. Trimmed and tied back the unused 12V TI wire (red).

10. Used ohmeter to check continuity between 5-pin DIN plug pins and the pins/grounds on the RCA cables. This is the source of the table earlier in this thread.

11. Heat shrinked and insulated connections in the final cable. Connected
the DIN plug to the console and powered it on. Checked for voltage on the
RCA cables to make sure I didn't have that 12V line shorted in.

12. Powered it all off, connected it to a display, and powered it up. All seems to be working despite the weird pinout. I don't have a speaker that takes RCA plug input and haven't had a chance to wire an adapter; I assume audio actually works...

Excuse my curiosity but I still have 8 lives left, so I should be good
:-D I rate it as highly unlikely that any NTSC console would have a
different pinout than the others - there wouldn't be any need for any such modification. (makes no difference whether beige or black/silver)

Please be curious. It's a mystery I'd like to solve. I've not yet had a chance to open the case, however I am inclined to agree with you and the
others that there's likely nothing unusual inside. Possibly this
evening...I expect I will find a problem internal to the cable, either with
my soldering work or at some other point. Unfortunately, I didn't probe
the DIN-RF board connections prior to cutting the cable.

Fact of interest, being in 50Hz land here: I have several 50Hz consoles
and one NTSC console, and it turns out that the PCB tracks are no different for the video output stage for the 50Hz model. You can pull the TMS9929A
and replace with a TMS9918A and get your composite NTSC output (got some of them VDP chips from China). You can even pull the 6-pin DIN connector and replace it with a 5-pin - the board is made to accommodate them both. I'd like to do a YouTube video on that sometime.

That is interesting, thanks for sharing it. I'm contemplating the move to
VGA output.

Tom

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Great, thanks for going to the trouble. So you used a multimeter. I'm still weirded out by that different pinout - if you learn anything more there, please let us know.

As a side note, I took a picture one doesn't see very often - the U.S. console's 5-pin DIN versus the European console's 6-pin DIN:
https://brian.tw/TI-99/4A/ntsc-vs-50Hz.jpg

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