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  • Joined: 17 Apr 2018
  • Posts: 10
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Measuring reset circuit voltage -JR?!
Post Posted: Sun May 13, 2018 8:07 am
Hi,

I’m tying to diagnose a dead master system 1 and have been following the service manual. One of the steps is to test the reset circuit and it says “measure the voltage at JR” and for the life of me I cannot see anything labelled JR on the board.

I’ve measured the voltage at the reset pin on the z80 but I’m not convinced that’s the same thing.

Anyone know where to measure this??
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  • Joined: 14 Aug 2000
  • Posts: 468
  • Location: Adelaide, Australia
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Measuring reset circuit voltage -JR?!
Post Posted: Mon May 14, 2018 10:21 am
I don't know where JR is either. I measure the reset pin on the Z80 and IC4 and IC5 to make sure no part of the system is being held in reset.
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  • Joined: 17 Apr 2018
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Post Posted: Mon May 14, 2018 10:49 am
I did think the reset lines were sensible to check - what are you looking for on those pins? For example on my board the reset pin on the z80
Seems to be 5v - is this reset being held on? What’s the process if it is?

I’m also confused as to whether this is the actual reset circuit (as in press reset and it does just that) or something else.

The service manual says the voltage should slowly rise to about 3.7 volts - that’s not the behaviour I’ve seen? I just wish it were obvious where to check!
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  • Joined: 14 Aug 2000
  • Posts: 468
  • Location: Adelaide, Australia
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Measuring reset circuit voltage -JR?!
Post Posted: Mon May 14, 2018 11:02 am
5 volts is good. The reset line is "active low" so zero volts or a loe voltage close to that would be the reset state.
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