TS1000's (ZX81's) black screen

Discussions about Sinclair ZX80 and ZX81 Hardware
dessony
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TS1000's (ZX81's) black screen

Post by dessony » Thu Jan 04, 2018 5:44 am

Hello everybody,

I have 3 set of TS1000 motherboards and a set of ZX81 motherboard. One of these motherboards is "dead". :cry: I also have a schematic for the certain computer. It is a Sams Computerfacts CC14. I also tested the computer's 4 ICs by putting them on the another known working board. These ICs were fine. I also read the ICs' sockets voltages off the known working board, which had its power applied, without its ICs in its place. I jotted each of the IC's voltage readings down on a piece of a paper for each IC. I also compared it against the "dead board". I discovered that a Z80 socket pin number 17 was dead. I traced it, on the schematic, to the TR1 section of the board. In my own opinion, the board had no clock pulse or "the computer has a heart attack". I plan to remove the components within the TR1 section area. I also would try to test these components and a few "tracks" or "traces" on the dead board to see what led to the board's not working.

Thanks,
DesSony

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Paul
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Re: TS1000's (ZX81's) black screen

Post by Paul » Thu Jan 04, 2018 8:08 am

Hi dessony,
pin 17 is the NMI. if this is open circuit or 5V then your zeddy should run in fast mode always.If it's alway low your zeddy wont show anything as its constantly executing Adress 66h in your ROM. In doubt just don't insert pin17 into the socket (bend it a little) for tests.
If Pin 6 (CLK) isn't pulsing (Voltage around 2.5 V on a slow Voltmeter) then maybe your ceramic filter of 6.5mhz is dead.
As it only a few pence i'd replace it if I were you.
HTH
Paul
In theory, there is no difference between theory and practice. But, in practice, there is.

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Paul
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Re: TS1000's (ZX81's) black screen

Post by Paul » Thu Jan 04, 2018 8:11 am

In case you want to sell the broken TS1000, Zxkim81 is searching for one. You could send it to me, I repair it and add a working rampack and send it to Zxkim81.
Maybe this way we can get a reasonable price for Zxkim81 .

Kind regards
Paul
In theory, there is no difference between theory and practice. But, in practice, there is.

McKlaud
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Re: TS1000's (ZX81's) black screen

Post by McKlaud » Thu Jan 04, 2018 10:22 am

:mrgreen: well, well, well ... :mrgreen: I think a few other guys on here would be interested in a broken TS1000 :twisted:

Before you start cannibalising the board check if the TR1 is fine.

What version of the ULA is there?
Claudius
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dessony
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Location: Indiana, USA

Re: TS1000's (ZX81's) black screen

Post by dessony » Fri Jan 05, 2018 8:57 am

Thank you for your responses to my recent TS1000's issue. This board is Issue 3. The board is set for the 2K RAM and NTSC and is marketed for the American side. But, the board can be set for PAL by removing only a resistor from the board and can be marketed for the European side. The board now has its modern switching mode device( no more LM7805 and its heat sink )! :D I removed a channel selection switch and a RF modulator's gut from the board. I installed a 1024MAK/DesSony video Buffer Transistor Amplifier board within the RF modulator. I tested a 1024MAK/DesSony board on another board with an excellent result! :lol: I also changed the keyboard contacts because old one had some corrosive issue. The ULA can be 184E or 210E depending upon the new owner's desire. Also, I put two new ele. cap., a new 6.5mhz ceramic filter, and 4 precision machine sockets on the board.

I have some issue with transistors. The board now has two NTE123A at this time. I like ZTX313 or MPS2369 better than NTE123A or NTE123AP because I have enough information on these 4 transistors. But, I have no idea where can I get these special transistors which does not have "NTE" label. I need your help on this one. :oops:

I might post a few pictures here.

Thank you very much in advance.

DesSony

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1024MAK
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Re: TS1000's (ZX81's) black screen

Post by 1024MAK » Sat Jan 06, 2018 12:38 am

The only source of ZTX313 or MPS2369 transistors appears to be eBay...

Mark

dessony
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Location: Indiana, USA

Re: TS1000's (ZX81's) black screen

Post by dessony » Sat Jan 06, 2018 9:33 am

Thanks Mark(1024MAK).

I just checked out a Futurlec website. I placed an order of the (10) MPS2369 and a (1 set of 10) MMBT2222A (for a future project of the 1024MAK/DesSony video buffer transistor amplifier board / SMD version).

Cheers,
DesSony

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1024MAK
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Re: TS1000's (ZX81's) black screen

Post by 1024MAK » Sat Jan 06, 2018 3:22 pm

Good that you have found a supplier of MPS2369 transistors. When I looked a couple of months ago, I could not find any that were in stock apart from on eBay.

Mark

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PokeMon
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Re: TS1000's (ZX81's) black screen

Post by PokeMon » Sat Jan 06, 2018 7:00 pm

You can order them quite cheap from Aliexpress:

https://de.aliexpress.com/item/100-teil ... 82982.html

100 pieces with 12 cent each - no shipment fee.

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1024MAK
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Re: TS1000's (ZX81's) black screen

Post by 1024MAK » Sat Jan 06, 2018 7:08 pm

PokeMon wrote:
Sat Jan 06, 2018 7:00 pm
You can order them quite cheap from Aliexpress:

https://de.aliexpress.com/item/100-teil ... 82982.html

100 pieces with 12 cent each - no shipment fee.
Thanks :D

Mark

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