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Are the schematics of TI99/4A accurate? Schematics for beige console

Schematics

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#1 hhos OFFLINE  

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Posted Wed Jan 9, 2019 9:48 AM

"My detailed study of them will show me that they were not reliable: Several errors slipped inside. The first step was a precise study of the logic of the microcomputer in order to detect all the errors. It was a very interesting step."

 

Fabrice Montupet made this statement in his TI(ny)-99/4A thread in June '17.  So far I have not found any errors in the schematic that I have.  I can imagine he has had many requests for details on his findings.  I do not wish to waste his time if he has already provided this information somewhere.  I did search for a while, and I found schematics for what I presumed was the PAL version of TI99/4A, because it had a TMS9928A.  But then I saw that it still had a 10.7 MHz crystal, so it couldn't be PAL.  A little research revealed that the TMS9929A is the PAL version of the 9928A.  Since Fabrice lives in France I further presume the PAL version would be the one he uses (I think I recall him saying somewhere that the 9929A was his favorite VDP ), and this schematic would be the one that has the errors?  Or perhaps he is referring to differences between the NTSC schematic and the PAL version?

 

I really just want to know if I need to be wary of errors in the NTSC schematic for now.  However, in my search for schematics, I have not come across any for the beige version of the TI99/4A.  I understand there were some significant changes made in how things are decoded in these units.  Is this info out there?  If so, where is it?

 

Thanks,

HH



#2 Willsy OFFLINE  

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Posted Wed Jan 9, 2019 12:01 PM

The Bunyard manual will probably be the best resource. It was written by one of the TI engineers that worked on the project, if I remember correctly. I think it's available in the resources thread.

 

Regards



#3 Willsy OFFLINE  

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Posted Wed Jan 9, 2019 12:04 PM

Found it in the TI PDF Repository.

 

Cheers

 

Mark



#4 fabrice montupet OFFLINE  

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Posted Wed Jan 9, 2019 2:58 PM

The official TI schematics are the same for the US and EU computers, they offers the information for both TMS9918A and TMS9929A VDP.

They contain several errors. One among them: you can see "-5V" for U607 (74LS74) pin #1, the right value is "+5". A second error still on the TI schematics, -INTREQ on TMS9900 pin#32 goes to U500 (GROM0)  pin #11, the right way is to U300 (TMS9901) pin #11.   There are still others.



#5 Ksarul OFFLINE  

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Posted Wed Jan 9, 2019 6:09 PM

One of the later technician's guides includes schematics for both the standard 99/4A board and the LCP board (also known as the QI board). I may have a copy of that around here somewhere. . .



#6 hhos OFFLINE  

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Posted Wed Jan 9, 2019 10:15 PM

Found it in the TI PDF Repository.

"It" would be the Bunyard book I take it?  That is the one that I have been using.

 

Thanks,

HH



#7 hhos OFFLINE  

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Posted Fri Jan 11, 2019 2:34 PM

I found this:

 

http://www.mainbyte....n/ti99_tech.pdf

 

It appears to be what I was looking for.  It has what appears to be a board layout for a 99/4, then schematics for a 99/4A, and then schematics for the 99/4QI.

 

Thanks,

HH



#8 Ksarul OFFLINE  

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Posted Sat Jan 12, 2019 1:34 PM

That's the one. . .



#9 fabrice montupet OFFLINE  

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Posted Sat Jan 12, 2019 4:23 PM

I found this:

 

http://www.mainbyte....n/ti99_tech.pdf

 

It appears to be what I was looking for.  It has what appears to be a board layout for a 99/4, then schematics for a 99/4A, and then schematics for the 99/4QI.

 

Thanks,

HH

This TI document contains errors, whose the ones I have found and mentioned here.



#10 hhos OFFLINE  

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Posted Sat Jan 12, 2019 6:55 PM

That's the one. . .

Thanks, Ksarul.

 

 

This TI document contains errors, whose the ones I have found and mentioned here.

Thanks, Fabrice.  I'll be wary.  Were any of the errors in the last six pages?  Those schematics of the TI99/4QI are the only part of this manual that I am using.  Can you direct me to a list of the errors that you have found?

 

HH


Edited by hhos, Sun Jan 13, 2019 9:45 AM.


#11 fabrice montupet OFFLINE  

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Posted Sat Jan 12, 2019 7:33 PM

The two errors that I have listed are the ones that jumped out at me, looking those schematics again when I saw your message.  
To return about two years ago. At the beginning, I had a project consisting to clean and validate the TI Schematics (the 4A ones, not the QI). Severals errors were found and while I haven't finished the project, a second project came to mind: make the 99/4A that I dreamed to have in the years 80, including all the features that I needed... And the Tiny-99/4A was born. The TI schematics were not still corrected but while continuing the job, I began to add  directly on them features like the 32 KB RAM expansion, Speech Synthesizer, expansion slots, RVB video out, then a Real Time Clock, and SuperAMS. So, the TI schematics have been drastically modified. Finally,  they became the ones of another computer. And for now, I have not planned to unveil the TIny-99/4A v2 schematics.







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