UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Computers

Notices

Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

Reply
 
Thread Tools
Old 25th Oct 2018, 2:24 pm   #21
Trigon.
Triode
 
Trigon.'s Avatar
 
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 48
Default Re: Retired Texas TI99/4A engineer needs help please.

Quote:
Originally Posted by Boater Sam View Post
I know nothing of the UA723C or the TL331 chips other than they are hard to source in dil package and that they seem so expensive that I may well be wasting my time trying to go any further with the repair,
The 723 is available from Farnell for less than a pound! - UA723C

As for the TL331C, it does seem surprisingly difficult to find (one on eBay for 5) , but is it actually deceased ? Have you checked to see if the output sawtooth is present ?

Cheers
Trigon. is offline   Reply With Quote
Old 25th Oct 2018, 2:44 pm   #22
Boater Sam
Dekatron
 
Boater Sam's Avatar
 
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,655
Default Re: Retired Texas TI99/4A engineer needs help please.

I don't have a Farnell account, is the UA724CNG4 the same chip or the UA724CN?
I have no knowledge of how TL331 works, I thought it was a comparator.
You say it should be generating an oscillating output? Presumably this is in the 20kc/s range to run the switch mode regulator chip?
Prices for these are crazy, is there a good reason?
__________________
Boater Sam.
BVWS Member

Last edited by Boater Sam; 25th Oct 2018 at 2:49 pm. Reason: added
Boater Sam is offline   Reply With Quote
Old 25th Oct 2018, 3:53 pm   #23
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,457
Default Re: Retired Texas TI99/4A engineer needs help please.

You don't need an account to buy from Farnell these days, Sam, those days are long gone. However you may be hit with carriage charges considerably higher than the price of the IC itself. You probably have to order goods to a minimum value (20) before carriage is not charged for.

As well as the uA723 there was also the LM723, so worth looking for those too.
SiriusHardware is offline   Reply With Quote
Old 25th Oct 2018, 6:56 pm   #24
Trigon.
Triode
 
Trigon.'s Avatar
 
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 48
Default Re: Retired Texas TI99/4A engineer needs help please.

Quote:
Originally Posted by Boater Sam View Post
is the UA724CNG4 the same chip or the UA724CN?
G4 is just one of the 'eco' suffices - basically means lead-free.
Quote:
Originally Posted by Boater Sam View Post
I have no knowledge of how TL331 works, I thought it was a comparator. You say it should be generating an oscillating output? Presumably this is in the 20kc/s range to run the switch mode regulator chip?
It is. It alternately charges/discharges C16, comparing the voltage with the reference set by R11, R15-20 and the positive feedback via R13 which creates the hysteresis defining the amplitude. The waveform is asymmetrical because the output is open collector, so it discharges via R14 but charges via R14+R12.
Quote:
Originally Posted by Boater Sam View Post
Prices for these are crazy, is there a good reason?
It's probably been obsolete for a very, very long time.

Cheers
Trigon. is offline   Reply With Quote
Old 25th Oct 2018, 7:40 pm   #25
Boater Sam
Dekatron
 
Boater Sam's Avatar
 
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,655
Default Re: Retired Texas TI99/4A engineer needs help please.

Looking at data sheet for TL331 I can't work out the pin out connections with the 99/4A diagram.
The one on the board is 8 pin dil, can't find a datasheet for this old device only smc.
__________________
Boater Sam.
BVWS Member
Boater Sam is offline   Reply With Quote
Old 25th Oct 2018, 7:55 pm   #26
Trigon.
Triode
 
Trigon.'s Avatar
 
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 48
Default Re: Retired Texas TI99/4A engineer needs help please.

Here you go:-

https://www.alldatasheet.com/datashe...TI/TL331C.html

Cheers
Trigon. is offline   Reply With Quote
Old 25th Oct 2018, 8:21 pm   #27
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,457
Default Re: Retired Texas TI99/4A engineer needs help please.

And a datasheet for the uA723:

http://www.ti.com/lit/ds/symlink/ua723.pdf

If you want to check the functionality of the uA723 you could always breadboard the basic linear regulator application circuit from page 5 of the datasheet. It just needs the IC and a handful of passive components. (Suggested component values are on page 4).

I'm not suggesting this could be used as a substitute for the original switching regulator design (It can only output 150mA maximum), just to use it as a way of functionally testing the IC before you go buying another one.

If the uA723 IC doesn't even work in that basic linear mode then you can probably say that it is dud.
SiriusHardware is offline   Reply With Quote
Old 25th Oct 2018, 9:16 pm   #28
Boater Sam
Dekatron
 
Boater Sam's Avatar
 
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,655
Default Re: Retired Texas TI99/4A engineer needs help please.

Thanks guys for your valued assistance. Where would we be without the forum.
If I can get all the monkeys waiting for brass welding out of the workshop this weekend I'll have a go at testing the chips. Even the spiders have died off.

If all fails I will have to see which way the guy wants to go with this,
Sam.
__________________
Boater Sam.
BVWS Member
Boater Sam is offline   Reply With Quote
Old 8th Nov 2018, 3:30 pm   #29
Boater Sam
Dekatron
 
Boater Sam's Avatar
 
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,655
Default Re: Retired Texas TI99/4A engineer needs help please.

Thanks to Ron (ronbryan) I now have 2 fresh 723 regulator chips. Very generously donated.
So I thought I would 'scope the oscillator chip first.
Cleared some space on a very cluttered bench for the scope and set everything up.
Bah! The Telequipment 'scope has gone up in smoke! The other one is buried under lots of radios that I have put away.

So I'm discouraged and getting pressed for time now, pretty sure that the oscillator chip, TL331 is not working either. Briefly fitting a 723 did nothing.

Got to pack up and mothball the workshop in preparation for going away for winter. Its going to have to wait till late March when I get back.
Thanks to all for the assistance. Watch this space next year!
__________________
Boater Sam.
BVWS Member

Last edited by Boater Sam; 8th Nov 2018 at 3:32 pm. Reason: Added
Boater Sam is offline   Reply With Quote
Old 16th Nov 2018, 4:36 pm   #30
dominicbeesley
Octode
 
dominicbeesley's Avatar
 
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,683
Default Re: Retired Texas TI99/4A engineer needs help please.

Sorry for the delay in getting back to you. I had a dig through the cellar today and I couldn't locate the modulator or PSU for the TI which means I've either lost them along the way or they've ended up in long-term storage. I did locate the TI itself if you want it?

I also located a water leak which has been doing damage to a few things so not a completely wasted task...
dominicbeesley is offline   Reply With Quote
Old 16th Nov 2018, 5:17 pm   #31
Boater Sam
Dekatron
 
Boater Sam's Avatar
 
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,655
Default Re: Retired Texas TI99/4A engineer needs help please.

Hello Dominic.
Wonderful, My pal would definitely like it, please PM me with what you want and can you send it?
I have a Hermes account.

No progress yet with the board, Its like "There's a hole in my bucket", first I need to fix the 'scope. I've ordered a LM339 to sub for the TL331.
Sam.
__________________
Boater Sam.
BVWS Member
Boater Sam is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 3:26 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.