VOGONS


First post, by Kidrash

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Greetings to everyone.
I'm having troubles resurrecting an Olivetti M290s with motherboard M203.
It simply not boot up, nothing on screen, no beeps.
The powersupply was in bad shape, capacitors leaked so the whole power board has been cleaned, neutralized and the capacitors replaced.
Now the voltages are stable but the board still not boot up.
The bios's chips seems to work as they have been read on multiprogrammer and compared with the bios in the collection found here.
The isa diagnostic card show "----", the processor warms up, power is on all the chips on the board.
There is some activity on the board. With a logic proble i tested some lines and there is "traffic" plus with a logic analizer i sniffed some data.
I made an adapter to read the eprom addresses and output (not at the same time, the analizer it's only 16 channel) and the first address i see it's fff0.
It's a bios parted in two chips, high and low, so i don't know exactly how to handle it yet.
Address line seems to be shared with both chips, but not the output. No continuity on the O lines between the 2 chips.
Still with the analizer i tried to sniff some data on the processor and what concern me it's the reset line wich is high almost all the time.
There are some "sparks" of low value in the first 1-2 seconds from powering on but if i read the line after a while it's stable to high.
The reset pin it's connected to chipset TACS82301pb , i can't find any datasheet.
http://www.dosdays.co.uk/topics/Manufacturers/ti.php it's the only information i get googling.
As tools i have a multimeter, the logic probe, the 16ch logic analizer and solder.
What else i can try?

Thanks anyone for any help.

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Reply 1 of 3, by SSTV2

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If the RESET signal is constantly HIGH, you won't get any signs of life from that motherboard, CPU is simply not fetching and executing any instructions from BIOS. You should check +5V Power Good (PG) signal coming from the PSU and all traces/circuitry related to it, as too low or absent PG will force chipset to halt CPU. System's clock generator could be at fault also.

Reply 2 of 3, by Kidrash

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For sure i will check again the PG again and all the voltages. I will do a custom connector and test with a different psu.
So if i get data on the Rom address lines means that the board does something and the reset goes down. I will check again with the logic probe and the logic analyzer.
Yesterday evening i "sniffed" again the rom, the LOW one, and on the address lines i captured some coerent data. The first address was FFF8. I'm a bit puzzled about that. Everywhere i read about reset vector talks about FFF0
If i open the bin file for the lower rom at that location (FFF8)i find the jump instruction., but in standard reset vector it's at FFF0.
I still have to understand well how a bios works when it's on 2 chips, one for low and one for high bits.
I'm having troubles to get the data on output lines, but the chips seems to be good cause the programmer can read them. I will work on the O lines to get some realiable data.
The system clock is the 14.something crystal i presume. If yes, it's connected directly to a tact chip of wich i can't find any datasheet. On the motherboard, where i can test the system clock? ISA bus? i simply hookup the logic analizer to the pins of the crystal?

Reply 3 of 3, by Kidrash

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After a good suggestion, i connected the logic analizer to the parallel port as this machine has a prescreen post and i grabbed some data.
0.205887750,(129)(0x81)
0.205937300,(131)(0x83)
0.205965600,(133)(0x85)
0.359668550,(135)(0x87)
0.523224100,(137)(0x89)
0.574552100,(139)(0x8B)
0.616640950,(141)(0x8D)
Time 0 is the reset line going down. I have no idea of what the codes refers to. Someone has a list that can share? Otherwise i have to learn how to disassembly a bios.