H5 possible reset issue (WIP)

[exxos]

Long story short I was monitoring the reset line on a spare 68K IO socket on my scope when I saw this...

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Two seconds later I heard my radio wireless clock beep.. Bit of a coincidence I thought..... Then the H5 reset.

I noticed similar earlier that if I strike my soldering iron while monitoring the falling edge of reset, I can clearly see some distortion there. Sometimes I can even get the H5 to reset.

The problem seems to be worse more towards the power supply. Have swapped out my own brand for a SR98 and same issues. The reset IC is under the PSU .

The import to the reset chip has a internal IC pull-up of 68K. Possible its not enough. But if the IC saw a post you would assume a proper reset pulse would trigger.. So there lies my ponder.. I don't have time at the moment to get sidetracked onto another project.....

The H5 has a 10K pull up on the reset output which feeds the LS07 buffers which drives system reset. The output of the LS07 has a 1K pull up on it. So a RF spike could only be most susceptible on the MR pin of the reset chips which has internal 68K pullup. I would think its unlikely a RF spike could counteract a 10K resistor even..

This is the reset IC

stm6315.pdf

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Circuit (it will vary a bit depending on H5 revision)

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So it would help if other people could actually replicate this experiment and see if it is repeatable on other people's machines.. Even a original Atari ST in comparison would help ..

[exxos]

This happens when I turned the bathroom light on !

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[Icky]

You sure you dont have dodgy electrics in your house @exxos

[exxos]

You sure you dont have dodgy electrics in your house @exxos

Yeah but im "isolated" via my UPSU on everything in my room.. and my gas soldering iron and radio controlled time clock also causes the issue.

[stephen_usher]

Are you sure it's not the UPS misbehaving then? Half switching to battery with a slightly different phase when it sees a spike on the mains?

[exxos]

Are you sure it's not the UPS misbehaving then? Half switching to battery with a slightly different phase when it sees a spike on the mains?

How does a gas soldering iron cause mains issues? And only on the reset signal?

[stephen_usher]

Ah, OK. I guess that it will have a piezo igniter.

So, it sounds like it’s an RF issue. Probably a cold joint somewhere acting as a crystal radio receiver.