H5 possible reset issue (WIP)
Posted: 30 Mar 2026 20:03
Long story short I was monitoring the reset line on a spare 68K IO socket on my scope when I saw this...
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
Circuit (it will vary a bit depending on H5 revision)
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 ..
- IMG_4947.JPG (97.76 KiB) Viewed 979 times
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- (177.45 KiB) Downloaded 27 times
Circuit (it will vary a bit depending on H5 revision)
- reset.PNG (44.81 KiB) Viewed 979 times
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 ..