ZX81 rebuild

[gammaray]

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....

[Lardo Boffin]

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.

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?

[1024MAK]

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]

I got them from eBay - new old stock:-

36E94B3A-372E-4DAB-A9A0-DB98CD1047E0.jpeg

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Always a gamble...

[Lardo Boffin]

With extra resistance I get:-

CADF4BCE-6F57-468F-90EA-BE0FE9E0DE49.jpeg

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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!

[Paul]

please excuse my stupid question: are the pin layouts equal?

[Lardo Boffin]

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.

Doh?

TR2.jpg (65.36 KiB) Viewed 4690 times

Hmmm.

[Paul]

Thats how it seems.

[gammaray]

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.

[Lardo Boffin]

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!