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Broken TI 99 4A - can you help me fix it?


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#1 RickR OFFLINE  

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Posted Wed Sep 11, 2013 4:12 PM

I just pulled my previously working TI out of the box and tried to use it, but it isn't working.  I'm using a composite cable, and I'm getting just a plain black screen and a high pitched tone on audio.  I did try a different power adapter, but got the same result.  Also tried another composite cable.  Any ideas on what I should check next?

 

Thanks.



#2 RobertLM78 OFFLINE  

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Posted Wed Sep 11, 2013 5:22 PM

U.S. or European configuration?

#3 RickR OFFLINE  

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Posted Wed Sep 11, 2013 5:29 PM

US.  I have a suspicion it's either the power switch or the power board. 



#4 RobertLM78 OFFLINE  

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Posted Wed Sep 11, 2013 10:49 PM

Check out this how to I posted a while back - hopefully that should have you up and running. I can't imagine that the machine wouldn't work after being in storage.
http://atariage.com/...omposite-cable/

Edited by RobertLM78, Wed Sep 11, 2013 10:49 PM.


#5 Willsy OFFLINE  

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Posted Thu Sep 12, 2013 2:24 AM

Check the voltages coming off the PSU board where they meet the motherboard (near the keyboard connector).

 

If the power supply checks out then it's almost certainly a blown VRAM in my experience (fixed a few over the years) which means getting a good, known to work VRAM, then, one at a time, remove (de-solder) a VRAM from the board, fit a socket, and fit the good VRAM and re-test. If it doesn't work, de-solder another, fit a socket, etc...



#6 mnbvcxz OFFLINE  

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Posted Thu Sep 12, 2013 7:30 AM

I read where someone suggested placing the new ram over the top of an installed ram so that all the legs made contact and apply the power, if it worked, you had found the faulty ram, if not then move the ram to the next chip and try again, it seems it would be quicker than desoldering and resoldering all the chips.



#7 Willsy OFFLINE  

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Posted Thu Sep 12, 2013 7:52 AM

I read where someone suggested placing the new ram over the top of an installed ram so that all the legs made contact and apply the power, if it worked, you had found the faulty ram, if not then move the ram to the next chip and try again, it seems it would be quicker than desoldering and resoldering all the chips.

Might work. I'd say it's 50/50. It just depends "how" the chip has failed. If that chip has failed such that it's driving the pin one way or the other it could possible cause contention between the same pins on the two devices. I don't think it would hurt to try it though.

 

I was also thinking, if you're just getting a blank screen, then another cause could be the 256 byte PAD ram (no RAM available for the 9900 to work with), or, very unlikely, the 9900 itself. I've never heard of a 9900 giving up the ghost though. They seem pretty bomb proof. Anyone?



#8 slinkeey OFFLINE  

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Posted Thu Sep 12, 2013 9:18 AM

Would a F18A fix bad VRAM? :P  Not suggesting it as it is an expensive solution.  I jut thought of it as an interesting thing to ponder.



#9 marc.hull OFFLINE  

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Posted Thu Sep 12, 2013 10:51 AM

 

I just pulled my previously working TI out of the box and tried to use it, but it isn't working.  I'm using a composite cable, and I'm getting just a plain black screen and a high pitched tone on audio.  I did try a different power adapter, but got the same result.  Also tried another composite cable.  Any ideas on what I should check next?
 
Thanks.

 


Unfortunately a black screamer can be caused by failure of almost any part in the machine from memory to control logic to the 9901 or 9900 or etc. The high pitch tone is your 9919's normal state at power on. It is not being reset so I doubt the power up routine is being executed nor any processing for that matter.

Some likely causes may be.....

Cart port is shorting out somewhere (Remove it and see if the machine boots.)

Power supply is bad (check for 5, -5, 12 and gnd at mobo. They are printed on the board by the brown wires.) Check this with the PS unconnected to the mobo and then when it is connected. Note any big difference. Be aware that a bad PS can show good voltages when unconnected but suddenly drop out when it is plugged in making it appear that the mobo has a short when it doesn't.. If it does drop out when connected and you are sure the PS is OK then check to see if a Cap is shorted on one of the rails (pull one end and check to see if it is good.) Feel for hot IC's indicating an internal short.


Stuck line(s) (check all control, clock, address and data lines in an attempt to find the culprit.) This one can be more or less a crap shoot tracking down the offender.

Good luck

#10 RickR OFFLINE  

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Posted Thu Sep 12, 2013 10:59 AM

Thanks for all the tips.  I'll get a multimeter out this weekend and see what I can find.  If it doesn't work out for me, does anyone have a spare TI they'd like to sell?  PM me.  Thanks.



#11 Asmusr OFFLINE  

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Posted Thu Sep 12, 2013 12:00 PM

If it doesn't work out for me, does anyone have a spare TI they'd like to sell?


This store has some very reasonable prices. I bought some cartridges from him a few months ago.
http://www.collector...w/TI-994A.html#

#12 Asmusr OFFLINE  

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Posted Thu Sep 12, 2013 12:05 PM

Would a F18A fix bad VRAM? :P  Not suggesting it as it is an expensive solution.  I jut thought of it as an interesting thing to ponder.


I had a console with a garbled video signal. I don't know if it was the VRAM or the 9918A that didn't work, but installing an F18A fixed it.

#13 matthew180 OFFLINE  

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Posted Thu Sep 12, 2013 1:55 PM

Yes, an F18A can be used to "fix" a console with bad VRAM, bad VDP, or failed component in the video output section. My F18A test console does not even have any VRAM installed (I completely removed the DRAMs).

As for the problem with your current system, Marc pretty much covered the main possibilities. Bad CPU, GROM, ROM, constant reset, short in the cart port, bad voltage, etc. The symptom is too vague without some testing. Start with the easy stuff (voltage testing, swapping socketed components, etc.) and hope for the best.

I had a bad GROM that caused this same problem and reseating the GROMs fixed it (the console GROMs are in sockets so they are easily swapped/changed).

#14 RickR OFFLINE  

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Posted Thu Sep 12, 2013 6:59 PM

Update:  It's still broken, but here's what I've found:

 

- The power adapter checks out fine

- The power board checks out fine

- The voltages at the motherboard are fine.  5, 12, and -5 as expected where the brown wires connect to the motherboard.

- I unseated and reseated the 5 socketed chips. 

- The cartridge connector has been removed.

- I most definitely do not have the skill to unsolder chips and solder in a socket.

 

I'm not sure where to go from here beyond starting to look for a new computer. 

 

Thanks.



#15 RobertLM78 OFFLINE  

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Posted Sat Sep 14, 2013 12:16 AM

I still can't help but wonder if the cable is the problem - you said composite, is that a "new" composite cable with the 5-pin din connection and two RCA jacks, did you make one, or, are you using some sort of 1/4" to RCA adapter with an old composite monitor cable? What you describe sounds a lot like what I experienced when I was making a "modern" composite cable (with two RCA jacks) from an spare RF modulator cable a few months back. Unfortunately I didn't crack open the RF modulator box to begin with to see how the wiring went, so I had a bit of a hard time getting it to work.

#16 RickR OFFLINE  

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Posted Sat Sep 14, 2013 8:24 AM

I still can't help but wonder if the cable is the problem - you said composite, is that a "new" composite cable with the 5-pin din connection and two RCA jacks, did you make one, or, are you using some sort of 1/4" to RCA adapter with an old composite monitor cable? What you describe sounds a lot like what I experienced when I was making a "modern" composite cable (with two RCA jacks) from an spare RF modulator cable a few months back. Unfortunately I didn't crack open the RF modulator box to begin with to see how the wiring went, so I had a bit of a hard time getting it to work.

I have two composite cables.  A home made one, and one from a C64.  Both worked fine before this, so I'm pretty sure that isn't the problem.  I don't have an RF cable anymore, so I can't test that for sure. 



#17 RobertLM78 OFFLINE  

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Posted Sat Sep 14, 2013 11:45 AM

I have two composite cables.  A home made one, and one from a C64.  Both worked fine before this, so I'm pretty sure that isn't the problem.  I don't have an RF cable anymore, so I can't test that for sure.

I see. Sorry that wasn't much of a help for you. I wouldn't worry about the RF modulator - it would be kind of redundant at this point. I would suggest going back over the things Marc suggested before looking for a new unit - hopefully you can get back TIing ASAP :).

#18 RickR OFFLINE  

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Posted Sat Sep 14, 2013 12:31 PM

I see. Sorry that wasn't much of a help for you. I wouldn't worry about the RF modulator - it would be kind of redundant at this point. I would suggest going back over the things Marc suggested before looking for a new unit - hopefully you can get back TIing ASAP :).

Appreciate you trying to help.  Thanks.



#19 ti99iuc OFFLINE  

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Posted Sat Sep 14, 2013 2:26 PM

Hi !

i had five TI99 with Black screen and pitched tone sound... now i have 4 ti99 repaired.

 

the great men repaired my ti99 is Xad Nightfall:  http://www.nightfall...erboard-faults/

 

meybe this web page could help ;)


Edited by ti99userclub, Sat Sep 14, 2013 2:28 PM.


#20 RickR OFFLINE  

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Posted Sat Sep 14, 2013 2:58 PM

Hi !

i had five TI99 with Black screen and pitched tone sound... now i have 4 ti99 repaired.

 

the great men repaired my ti99 is Xad Nightfall:  http://www.nightfall...erboard-faults/

 

meybe this web page could help ;)

Graci



#21 repetto74 OFFLINE  

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Posted Mon Oct 2, 2017 7:56 AM

Hi,

 

I have the exact same problem with a TI99/4A machine. Black screen on boot up and continuous beeping sound. I have swapped all socketed chips to a TI99/4A working board and those chips are good (GROM, VDP and Sound chip). 

I would like to test the PSU board now. I wanted to swap the PSU board with the one coming from the working TI99/4A but the two PSU board looks different, the one of the faulty machine looks like being the old model of the TI99/4 despite de fact it is mounted on a machine with the TI99/4A logo on it but I do assume that voltage outputs are the same. I cannot directly hook up the PSU of the good TI99/4A to the faulty one because the connector are not the same.

On the suspect PSU board the connection is done via a molex connector to hook up the motherboard while on the other PSU the connector is soldered on the PSU board (on the other PSU I have wires soldered and connected to the Molex)

Where do I need to measure voltages on the MB? I should check then for +5,-5 and 12 V right? So one lead of the multimeter on the GND pin and one on each pin to test the voltage?  :?  Sorry to ask I do have some basics in electronics but need a refresh.

 

Thanks

Rick






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