486-VIO-GT Motherboard with hot resistor pack(s)? \ VOGONS

486-VIO-GT Motherboard with hot resistor pack(s)?

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First post, by donny

Posted on 2022-12-28, 16:38

donny Offline

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Hi there !

I wanted to shared an observation on my 486-VIO-GT motherboard, when running.
I observed the board with some thermal imaging cam and noticed that two resistor networks (or resistor packs ? RP20 + RP21) get quite hot (>50 Celsius) after few minutes.
This does not feel normal, or is it? All other resistor networks on the board keep absolutely cool. Nothing exceeds those two components, temperature-wise, on the whole board.
Do you have any suggestions or experience with such an behaviour?
I might add: The board works fine. I checked all the jumpers against the manual I found in Ultimateretroweb, and everything seems to be correct (CPU type, Clock etc.).

PS: 4 pictures attached.

Many thanks in advance and Greets,
Sebastian

Reply 1 of 6, by majestyk

Posted on 2022-12-28, 16:49

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Do they still get hot when the cache / TAG chips are absent?

Reply 2 of 6, by donny

Posted on 2022-12-28, 17:48

donny Offline

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Hi !

Thanks for your quick suggestion, nice idea. I just tried that, and measured as well as touched them again.
For short: Behaviour unchanged. Quickly rising in temperature after power-on.
I dared to wait a little bit more (30 Mins): It seems as that it peaks at ~56 Celsius and is holding it there.
Don't know what to think of that...

Regards,
Sebastian

Reply 3 of 6, by majestyk

Posted on 2022-12-28, 18:37

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Have you tried with a different set of memory sticks?
What´s the resistor value printed on the arrays?

Reply 4 of 6, by donny

Posted on 2022-12-28, 19:01

donny Offline

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The description reads: 10Z221/331G (Yageo), on both of them.
Switching the RAM e.g. to the 72-pin bank didn't change behaviour.

Reply 5 of 6, by majestyk

Posted on 2022-12-28, 19:52

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221 means 220 Ohm, if the resistors would be between 5V and ground (worst case) each resistor would dissipate 0.11 W power. These arrays are rated for 0,125 W so this would still be within specs. The whole array would dissipate 0.99 W hence the temperature.

Are you sure the mainboard is a 486-"VIO-GT" and not GIO-VP, GIO-VT or GIO-VT2?

Reply 6 of 6, by donny

Posted on 2022-12-29, 07:38

donny Offline

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Good Morning! Thanks for the resistor info, wasn't to interpret it that way.
Yes, I'm sure regarding the board type:

Edit: Ohh, now I see. I mixed it up in the first post 😀 My bad.

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