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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??

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.

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!

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.

Author	Message
chunder_jacket Joined: 17 Apr 2018 Posts: 10	Measuring reset circuit voltage -JR?! Posted: Sun May 13, 2018 8:07 am
chunder_jacket Joined: 17 Apr 2018 Posts: 10	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??

asynchronous Joined: 14 Aug 2000 Posts: 741 Location: Adelaide, Australia	Measuring reset circuit voltage -JR?! 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.

chunder_jacket Joined: 17 Apr 2018 Posts: 10	Posted: Mon May 14, 2018 10:49 am
chunder_jacket Joined: 17 Apr 2018 Posts: 10	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!

asynchronous Joined: 14 Aug 2000 Posts: 741 Location: Adelaide, Australia	Measuring reset circuit voltage -JR?! 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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