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TI99/4A PAL Clock generator


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#1 repetto74 OFFLINE  

repetto74

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Posted Sat May 5, 2018 5:13 AM

Hi Guys,

 

I am buying some spare parts of the TI99/4A to have them available for any repair needs. I have found some e-bay resellers in China with VDP chip, Clock generator, CPU and rams. I have tested successfully the VDP chip (does not look as a new old stock but a new manufacturing) but the clock generator fails (black screen and continuous tone on power up). Now I would like to be sure the one I purchase is the correct because the marking is different. The E-bay clock generator is marked TMS9904ANL while the original one is marked TIM9904ANL. Are they different then or is the e-bay clock generator a scam?

Thanks,

Rick



#2 HOME AUTOMATION OFFLINE  

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Posted Sat May 5, 2018 6:23 AM

Ahh yes, Parts from Shenzhen province. I personally swear by them, sometimes at them!

TIM9904ANL is the part # I am familiar with. I just double checked.

I have had some luck with parts from China. Sometimes success can be found by doubling-up discrete parts or piggybacking Integrated Circuits.

Smaller sized breadboards have tested with resistances as high as 3 Ohms per hole,suitable only for L.E.D.s.

  Good Luck!


Edited by HOME AUTOMATION, Sat May 5, 2018 6:25 AM.


#3 repetto74 OFFLINE  

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Posted Sat May 5, 2018 10:42 AM

HI Home Automation,

 

Both IC's comes from the same reseller and I barely do not think tahat they mix good and bad IC's. I am somehow convinced that the TMS9904ANL is not the proper clock generator suitable for the TI99/4A.



#4 HOME AUTOMATION OFFLINE  

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Posted Sat May 5, 2018 11:00 AM

Besides backing up bad sections of internal circuitry, piggybacking can increase drive currents, sometimes knockoffs don't provide enough drive current.

Slim chance but maybe...



#5 repetto74 OFFLINE  

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Posted Sat May 5, 2018 12:05 PM

So you mean I may try to piggypack the original clock generator with the new one?



#6 HOME AUTOMATION OFFLINE  

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Posted Sat May 5, 2018 12:19 PM

I didn't know there was still an original. That could be more problematic I suppose.

I was thinking... "two knockoffs are better than one", sometimes.
 

Sort of a last resort if unsure.



#7 repetto74 OFFLINE  

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Posted Sat May 5, 2018 12:29 PM

Yes I do have the original still working. I am just buying spare parts whenever I found them just in case :-)



#8 Ksarul OFFLINE  

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Posted Sat May 5, 2018 7:27 PM

TIM9904 is definitely the correct part number. . .anything purporting to be a TMS9904 is definitely a knockoff of questionable value (some knockoffs work, some don't). I have past experience with TMS9909s being totally useless knockoffs (disk controller chips used in the Powertran Cortex). The originals are TMX9909s, and generally very hard to find (and ALL of the knockoffs of this chip I've seen are junk, as they didn't have an original to try and copy). I haven't bought any TIM9904's lately, as I got a small supply of them from a known good source a few years ago when they were selling off their excess TMS99XXX stock. If you need good TMS9900 chips, look on eBay for S9900 chips. There is a US seller that usually sells them in groups of four for $10, and they are original chips. He doesn't always have them in his store, but they pop up pretty regularly there (milpartsonline).



#9 repetto74 OFFLINE  

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Posted Sun May 6, 2018 5:00 AM

Hi Ksarul,

 

Thanks for your answer which is confirming what I was thinking :-). I definitely assume that TMS9904 will not work as should the original TIM9904. TIM9904 are hard to find, I hear that there is apparently an alternative 74LS362 which can do the same job. Is that true?



#10 Ksarul OFFLINE  

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Posted Sat May 12, 2018 7:58 PM

Every reference I've ever seen indicates that it is also known as a 74LS362, although I've never personnaly tried one as I still have a few TIM9904s that I bought a few years ago. You might want to test your TMS9904 chips in a logic tester set to test the LS362--that will at least tell you if any of the chips you got actually work. . .I do know that the TOPWIN3000 EPROM Programmer will test most of the chips in the 74LS chip family.



#11 Ksarul OFFLINE  

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Posted Mon May 14, 2018 9:18 AM

I just bought a large number of TIM9904/74LS362 chips on eBay from a seller I've bought a lot of HTF parts from before (jaxele). The chips have both numbers on them. I'll try and test them once they come in to verify function. Here's one from Italy with a reasonable price as well.



#12 Stuart OFFLINE  

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Posted Mon May 14, 2018 4:36 PM

The TIM9904/74LS362 are early versions and need a 48 MHz crystal. The later TIM9904A needs a 12 MHz crystal. So check the markings on the crystal and that will show which version of clock chip you need.

 

The TMS9904ANL is definitely a Chinese knock-off. But some of them do actually work fine (in the short term at least).



#13 matthew180 OFFLINE  

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Posted Mon May 14, 2018 5:12 PM

So you mean I may try to piggypack the original clock generator with the new one?

 

No, I would not do that.  Electronics don't work that way.  There are some situations where that might work, but in general it won't work and is a bad idea.



#14 Ksarul OFFLINE  

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Posted Mon May 14, 2018 5:26 PM

Here's a seller with the TIM9904ANL. I've bought from this seller before. Some stuff is really good--some not, but almost everything I've bought from them worked (with the exception of their 27C160 chips, which worked fine as 16-bit chips but failed to operate in 8-bit mode).



#15 repetto74 OFFLINE  

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Posted Wed May 16, 2018 8:52 AM

Hi Ksarul,

 

Thanks for the info. I bought a couple of TIM9904ANL a week ago from the same seller of your link :-). So waiting for them to test. I have a programmer which is the TL866 and do not know if it can test also. I will keep in mind the 74LS362 as a probable replacement also :-)

The TIM9904/74LS362 are early versions and need a 48 MHz crystal. The later TIM9904A needs a 12 MHz crystal. So check the markings on the crystal and that will show which version of clock chip you need.

The original TIM is marked TIM9904ANL so I assume it is the one for a 12 Mhz crystal. Next time I will crack open the TI99/4A I will give this a look ;-)

 






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