ZX81 rebuild

Discussions about Sinclair ZX80 and ZX81 Hardware
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gammaray
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Location: Texas

Re: ZX81 rebuild

Post by gammaray » Tue Dec 05, 2017 6:39 pm

How about testing with a base resistor less than that and adding a variable pot in series. Testing for middle of the road operation then get accurate ohms and then maybe a math. model given the char's of this TR2 and the ZTX313.

Then again maybe I shouldn't be so lazy and do it myself....
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

Lardo Boffin
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Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Tue Dec 05, 2017 9:52 pm

I will check tomorrow that it actually works with 4k4 of resistance as opposed to just the pin showing a pulse.
In the meantime I found some ZTX313s on ebay (new old stock) so may end up putting one of those in just to be sure! Had there been any for sale when i was buying all the stuff I would have bought some. :D

A variable resistor makes sense but I don’t have one lying around.

I believe the Ms2369 and the ZTX have similar voltage and amp requirements (based on what I can find on the web) so wouldn’t the current behaviour potentially signify a problem with the MS2369? Or is it down to the requirement to drive the MS2369 to the limits of it operating parameters to get it to work quickly enough?
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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

Re: ZX81 rebuild

Post by 1024MAK » Wed Dec 06, 2017 1:22 am

ZTX313 datasheet http://hardware.speccy.org/datasheet/ztx313.pdf
The important bit from the datasheet in this application, is:
Max. Storage time (tstg),
Max. Turn-off time (toff).
For a ZTX313 these are 13ns and 18ns respectively.

MPS2369 datasheet http://www.mouser.com/ds/2/308/mps2369-d-1193964.pdf
This, according to the datasheet, has a Max. Storage time (TVs) of 13ns.
And a Max. Turn-Off time (toff) of 18ns.

So it should be fine. But it is possible that the transistors that you have, are not as good as the transistors specified values in the datasheet. Can you post a picture of your transistors? Where did you get them from?

Note that I am not aware of any off the shelf transistor tester that actually tests the turn-off time of a transistor.

Mark

Lardo Boffin
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Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Wed Dec 06, 2017 10:21 am

I got them from eBay - new old stock:-

36E94B3A-372E-4DAB-A9A0-DB98CD1047E0.jpeg
(2.23 MiB) Downloaded 314 times
Always a gamble...
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Lardo Boffin
Posts: 714
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Wed Dec 06, 2017 10:26 am

With extra resistance I get:-
CADF4BCE-6F57-468F-90EA-BE0FE9E0DE49.jpeg
(692.25 KiB) Downloaded 314 times
So a definite improvement!

Either
1) The timing is still not quite right
or
2) It is but I broke something doing all this...

I think discretion being the better part of valor I may just wait for the ZTX313s to arrive and fit one of those and hope it was 1) above!
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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Paul
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Joined: Thu May 27, 2010 8:15 am
Location: Germanys west end

Re: ZX81 rebuild

Post by Paul » Wed Dec 06, 2017 2:19 pm

please excuse my stupid question: are the pin layouts equal?
In theory, there is no difference between theory and practice. But, in practice, there is.

Lardo Boffin
Posts: 714
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Wed Dec 06, 2017 2:53 pm

Paul wrote:
Wed Dec 06, 2017 2:19 pm
please excuse my stupid question: are the pin layouts equal?
There are no stupid questions!

I checked it about 5 times before soldering however having put the layouts next to each other it looks like I have installed it the wrong way round? I installed it with the same orientation as the ZXT313 but looking at it the MS2369 has opposite pins. :oops:

TR2.jpg
Doh?
TR2.jpg (65.36 KiB) Viewed 424 times
Hmmm.
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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Paul
Posts: 929
Joined: Thu May 27, 2010 8:15 am
Location: Germanys west end

Re: ZX81 rebuild

Post by Paul » Wed Dec 06, 2017 3:07 pm

Thats how it seems.
In theory, there is no difference between theory and practice. But, in practice, there is.

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gammaray
Posts: 433
Joined: Sun Apr 17, 2016 2:44 am
Location: Texas

Re: ZX81 rebuild

Post by gammaray » Wed Dec 06, 2017 4:19 pm

I was going to ask this but I thought it was a stupid question and wasn't my place and didn't want to risk being wrong since the drawing I had led me to believe it was the same.


I installed a trans' backwards once to make a "Why Wait" circuit and strangely still got the speed increase but the top screen lines were sheared to the left.

Corrected and worked perfectly.
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

Lardo Boffin
Posts: 714
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Wed Dec 06, 2017 5:16 pm

I am new to this so if someone points out I have got something wrong then I am glad to learn. Well, so long as they are polite! :D
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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