[TheRealAnubis]

Hi,

I just got my first TI-99 and it doesn't work. Tested the power supply - good, tested the internal power board - good. No video (black screen), and the sound IC gets incredibly hot in about 10 seconds.

The sound IC is SN94624N and the video IC is TMS9918ANL.

I'm not finding a source for the audio chip at all, and all of the video IC's seem to be in Hong Kong.

I wrote TI and asked if the SN76489 is considered a drop in replacement for this IC, but I haven't heard from them yet...

Anyone have any working spares?

[ksarul]

The SN76489 is not a direct drop-in replacement for the SN94624, as the SN94624 has a max clock speed of 500 KHz, while the SN76489 has a divide by 8 added to the clock input to allow the system clock to be working at up to 4 MHz. There are three chip designators you can use: TMS9919, SN94624, and SN76494--all of these have the 500KHz clock speed. I see one seller with the 76494s on eBay right now (there is also a US seller that occasionally has one for sale, but I haven't seen the one he had left up for sale lately, so he may have sold it).

The TMS9918A chips show up a lot--and even the Chinese ones are often fully functional chips. I don't have any spares at the moment of either chip, unfortunately.

[TheRealAnubis]

Thank you for the information! I've went ahead and ordered the IC's - I'll post back with the results.

[TheRealAnubis]

I have more 'repair' type questions, so I'm going to post in the hardware section. Thanks!

UPDATE - The VDP arrived and had a broken pin, so another one is on the way. Grrrrr....

[TheRealAnubis]

Well, I finally heard back from TI - kind of depressing, really -

I have been unable to locate any information regarding the SN94624N or the SN76489. I apologize for any inconvenience that this causes you.

This may be because the parts have been obsolete for quite some time, or they may be custom devices. We do not keep any data regarding obsolete devices since we do not support any obsolete devices. If these are custom ICs, we would not have this data since that data would belong to the person or company for whom the custom ICs were made.

I hope this information is helpful to you. Thank you for contacting TI Support.

Ahhh well.. So much for history!

[ksarul]

Here's a link to the datasheet for the SN76494/SN76496. That will get you what you need:

http://www.datasheet4u.com/datasheet/S/N...s.pdf.html

I'm sort of good at digging though the Internet to find obscure data--but in this case, I also have the book from which the reference is derived.

[TheRealAnubis]

Here's a link to the datasheet for the SN76494/SN76496. That will get you what you need:

http://www.datasheet4u.com/datasheet/S/N...s.pdf.html

I'm sort of good at digging though the Internet to find obscure data--but in this case, I also have the book from which the reference is derived.

Nice! Thanks for that! I was just thinking that TI would have some cool info on their own stuff... Silly me...

[ksarul]

Has there been any progress on your repair action? I just got an original SN94624 sound chip (someone pulled it from a working console they were dissecting) so that I would have a spare (for the first time ever, as that isn't a chip I've seen very often).