TS 1000 bad ULA?

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gary2000
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TS 1000 bad ULA?

Post by gary2000 » Sun Jun 19, 2016 4:45 pm

Hi, I bought a TS 1000 and used it for the first time since around '83.

I performed a composite mod on it like the common diagram available... it works great for about 20 minutes and it seems as though the ULA heats up, then character starts flickering and wavy lines go through the screen, then it loses picture completely.

Could the ULA be damaged?

Gary

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sirmorris
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Location: oxon, uk

Re: TS 1000 bad ULA?

Post by sirmorris » Sun Jun 19, 2016 4:51 pm

Hi Gary, welcome aboard!

It could be the ULA, especially if the computer still works while the display is wonky.

Power can also be an issue, regulators have been known to start misbehaving when they heat up.
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

Moggy
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Re: TS 1000 bad ULA?

Post by Moggy » Sun Jun 19, 2016 4:59 pm

Hi Gary welcome also. :D


A similar thing happened to me when the power pack got warm,I recall it was the smoothing capacitor in the power pack that gave up the ghost.

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sirmorris
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Location: oxon, uk

Re: TS 1000 bad ULA?

Post by sirmorris » Sun Jun 19, 2016 10:26 pm

^^ What Moggy said!
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

Moggy
Posts: 1507
Joined: Wed Jun 18, 2008 1:00 pm

Re: TS 1000 bad ULA?

Post by Moggy » Sun Jun 19, 2016 10:38 pm

Hells bells !! Charlie actually agrees with something I said.

Consider yourself promoted to Viscount Morris. :lol:

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sirmorris
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Location: oxon, uk

Re: TS 1000 bad ULA?

Post by sirmorris » Mon Jun 20, 2016 10:45 am

Mint or orange? :D
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

gary2000
Posts: 10
Joined: Sun Jun 19, 2016 3:46 pm
Location: USA

Re: TS 1000 bad ULA?

Post by gary2000 » Mon Jun 20, 2016 2:10 pm

Thanks, I'll have to check into that.

It would be nice if ULA is not bad... other units are cheap, but not that cheap. May be time for an inexpensive ULA replacement (like PLA has available for C64).

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: TS 1000 bad ULA?

Post by 1024MAK » Mon Jun 20, 2016 11:23 pm

Andy Rea has a design (he was selling them at one stage), RetroTechie has a design (I'm sure he will pop up and provide a link to his web site soon). And some other people have come up with their own versions.

A limited number of NOS ULA chips are available (but they are not cheap).

A basic digital multimeter does not cost much these days. No good for use on 240V AC supplies (for safety reasons), but okay for DC voltage and resistance measurements.

Measure the output of the power supply unit with it connected to the ZX81 (on the socket contacts on the ZX81 board). Post here the results as follows:-

These voltages are taken on the socket contacts on the ZX81 board:
DC voltage (20V range) just after power on,
AC voltage (20V or 2V range) just after power on,

After it starts giving problems...
These voltages are taken on the socket contacts on the ZX81 board:
DC voltage (20V range),
AC voltage (20V or 2V range),

DC voltage (20V range) between the right hand lead / leg (pin 3 in the diagram below) of the 7805 voltage regulator. Use the metal tab that connects to the square metal heatsink for the negative meter lead.

Code: Select all

 _____
|     |
|  O  |
|_____|
|     |
|7805 |
|_____|
 | | |
 | | |
 | | |
 1 2 3
 viewed from top/front
 
 1 is the DC input
 2 is the 0V terminal (heatsink tab also connected internal to this pin)
 3 is the +5V output
Then post your results here ;)

Mark

gary2000
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Location: USA

Re: TS 1000 bad ULA?

Post by gary2000 » Fri Jul 08, 2016 4:04 am

Ok. I'm back with some results...

VR: (1/ 3)
Cold. 10.27v/ 4.98

Hot. 10.63/ 4.93

At socket (DC):

10.48 cold/10.65 hot

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: TS 1000 bad ULA?

Post by 1024MAK » Sat Jul 09, 2016 7:26 am

Those DC voltages are in the acceptable range.
Did you record the AC ripple values (using the AC voltage or mV range)?

Mark

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