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Old 17th May 2021, 11:45 pm   #88
ortek_service
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Default Re: Early EPROM programmer.

Quote:
Originally Posted by SiriusHardware View Post
The 'Low' input voltage which feeds the regulator (TR5 and associated) is perhaps higher than I might have guessed it would be, my guess would be around 8V-9V. The reverse / overvoltage protection diode for that supply input (DZ4) is 18V, a bit more headroom than I would have expected but maybe that just shows that the 'low' input supply is unregulated, as an unregulated supply which is nominally 9V on full load could easily knock out 13V-14V when lightly loaded.
What voltage did you see for the Unregulated voltage input to the 5V regulator?
- I couldn't quite read it, as it was just of-shot of the original hi-res photo that had captured most of this.

And full version was too Low-Res. to read
- I couldn't tell if it was +5V4 or +5?V 4A (In which case regulator wouldn't do much, more of a limiter).

I can't see the point of using a LDO discrete-transistor regulator circuit, rather than a (nearly 3V dropout) 7805, if they were going to use 9V (even though many computers of that era did this). Unless they needed > 1A current of 7805 (and 2A / 3A etc. variants hadn't seemed to have been made back then).
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