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First post, by Bernkastel7734

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Hello,
I'm having hard time trying to fix Socket 3 motherboard HOT-419 made by Shuttle.

The problem I'm having is with reset signal ( I guess).
So, the board seems to be dead, no numbers running on POST analyzer card. CPU is getting
proper voltage and clock signal.
The problem is that reset pin on ISA slot ( B02 RESET DRV) is acting weird. If I am correct it should go high and then go low for proper reset, but on that board it is stuck somewhere in the middle ( 2,5V~2,7V).

If I am not mistaken such motherboard use PowerGood signal for reset. So I have check and PG signal is 4,7V and it's going to OPTI 82C895 pin labeled PowerGood.

I was trying to trace from where reset signal comes to ISA slot but I cannot find anything.

Do You have any ideas or suggestions how to diagnose reset circutry?

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Reply 1 of 9, by mkarcher

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Bernkastel7734 wrote on 2022-08-16, 10:45:

If I am not mistaken such motherboard use PowerGood signal for reset. So I have check and PG signal is 4,7V and it's going to OPTI 82C895 pin labeled PowerGood.

I was trying to trace from where reset signal comes to ISA slot but I cannot find anything.

Do You have any ideas or suggestions how to diagnose reset circutry?

Looking at the 82C895 datasheet, page 15, ISA bus reset is generated by the ISA bus buffer chip, but you are looking at the host system management controller. OPTi suggest to route PowerGood to both of these chips. Your HOT-419 uses the Opti 82C602 for ISA bus control purposes, just as recommended in the 82C895 datasheet.

The 82C602 datasheet requires PowerGood to be routed to the input pin 23, and the output pin 76 should be routed to the ISA bus. As I see that your board has a removed NiCd battery and some bodge wires, I suspect that the trace between pin 76 of the 82C602 and the ISA RESETDRV pin has been corroded from battery leakage and needs to be bodged, too.

The voltage you see at RESETDRV is plausible to result if no output is driving the line, and a chip with TTL-compatible input is connected to it.

Reply 3 of 9, by Bernkastel7734

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mkarcher wrote on 2022-08-16, 11:13:

The 82C602 datasheet requires PowerGood to be routed to the input pin 23, and the output pin 76 should be routed to the ISA bus. As I see that your board has a removed NiCd battery and some bodge wires, I suspect that the trace between pin 76 of the 82C602 and the ISA RESETDRV pin has been corroded from battery leakage and needs to be bodged, too.

Thanks a lot! So, I have checked and the PWRGOOD arrives to 82C602. After a power up pin 76 goes high for a second and then is low - so that means there is a connection problem between pin 76 and ISA slot

Reply 7 of 9, by mkarcher

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Bernkastel7734 wrote on 2022-08-16, 22:44:

It would be too great if it started working after broken trace fix. Now it is reseting but still no numbers on the POST analizer

Sounds like more bad traces. Right next to pin 76 carrying the active high ISA reset signal, the 82C602 has pin 75, carrying an active low reset signal that is meant for the CPU and the VL slots. You might need to check that one, too.

If inspection of traces next to the broken ones you already spotted won't help: You might then try to measure whether you get FSB activity (check ADS, available at th VL slots for example), should be a tidbit below pins that are always at high level, because every cycle starts drops this pin for a brief amount of time. If the 486 operates, it starts so many bus cycles that you can see the average going down. If FSB activity is there, the next thing to check is ROM selection: Both /CS and /OE on the BIOS chip need to be pulsing, too, at least for a split second after pushing the reset button. This information can help you narrow down at what place the process fails. Don't forget the most obvious things, though: The CPU and the BIOS ROM need to be firmly seated in their sockets.

Reply 8 of 9, by Ydee

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Bernkastel7734 wrote on 2022-08-16, 10:45:
Hello, I'm having hard time trying to fix Socket 3 motherboard HOT-419 made by Shuttle. […]
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Hello,
I'm having hard time trying to fix Socket 3 motherboard HOT-419 made by Shuttle.

The problem I'm having is with reset signal ( I guess).
So, the board seems to be dead, no numbers running on POST analyzer card. CPU is getting
proper voltage and clock signal.
The problem is that reset pin on ISA slot ( B02 RESET DRV) is acting weird. If I am correct it should go high and then go low for proper reset, but on that board it is stuck somewhere in the middle ( 2,5V~2,7V).

If I am not mistaken such motherboard use PowerGood signal for reset. So I have check and PG signal is 4,7V and it's going to OPTI 82C895 pin labeled PowerGood.

I was trying to trace from where reset signal comes to ISA slot but I cannot find anything.

Do You have any ideas or suggestions how to diagnose reset circutry?

If you need to measure anything, let me know, I think we have the same board. Mine is in working condition.

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Reply 9 of 9, by Bernkastel7734

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Ydee wrote on 2022-08-18, 10:11:

If you need to measure anything, let me know, I think we have the same board. Mine is in working condition.

Thanks a lot. In deed seems to be the same board, if needed will let You know!