RickNel
Veteran Member
I've not had a working 486 mobo for a while, and just picked up a generic one that looks in near-original condition. It's branded "US Technologies" (sure sign it wasn't made in USA) and model TK 82C480 - with UMC 82C480 chipset. There's a description and photo of it in the collection hosted at www.redhill.net.au, and I found a perfect visual match for it under the "Informtech" brand in the TULARC archive of ISA/VLB motherboard jumper pinouts
BUT
I can't get any boot video signal out of it, having tried several VGA and a VLD video cards in it.
I don't have a compatible board to swap socketed components - ie Intel DX 33 CPU, 8 x 4Mb RAM, 256k cache RAM.
Here's what I've already done trying to isolate problem:
1. Found visual match for the board on TULARC and checked all jumpers are correct for identified components
2. Tried adjusting mobo VLB wait-state on/off
3. Checked keyboard flashes LEDs as expected on power-up and system power/turbo LEDs and switches function correctly.
4. Checked all three oscillators (system, bus and I guess keyboard) with oscilloscope for clean signal.
5. Verified 33MHz present on ISA bus pin 30 (OSC)
6. Found no clock signal present on ISA bus pin 20 (CLK) with no boards in bus.
7. Touch-tested CPU and chipset chips all about as warm as expected.
8. Pulled AMIBIOS ColorBIOS 27C512 from socket and read it - seems OK so far as all ASCII data in the BIOS can be seen without errors.
I'm an 8-bit kind of guy and not too familiar with ISA hardware. What tests can I make to locate faults?
The motherboard has no jumper to enable/disable VLB video. Should I expect to see a VGA video BIOS message when trying a VGA card in the ISA bus?
I'm trying a Trident VLB video card based on TGUI9420, but with no docs found yet . Jumpers as follows:
1. Select STMB (two options of ARP/BRP configurations - are these on-board memory configs or upgrade option configs - there are a couple of unpopulated 40-pin SMC locations on the PCB?)
2. Select I or NI (is this interrupt/non-interrupt mode?)
3. Select +RAS on/off (what is this?)
4. Select Fast clock on/off
It would be nice to get a VLB video card working after all these years.
As to the motherboard, I'll only write it off if there are faults in the surface-mount UM chipset. Anthing socketed or minor discrete components I will try to replace, if I have a working board chipset.
Is there a standard procedure for this sort of trouble-shooting?
Rick
BUT
I can't get any boot video signal out of it, having tried several VGA and a VLD video cards in it.
I don't have a compatible board to swap socketed components - ie Intel DX 33 CPU, 8 x 4Mb RAM, 256k cache RAM.
Here's what I've already done trying to isolate problem:
1. Found visual match for the board on TULARC and checked all jumpers are correct for identified components
2. Tried adjusting mobo VLB wait-state on/off
3. Checked keyboard flashes LEDs as expected on power-up and system power/turbo LEDs and switches function correctly.
4. Checked all three oscillators (system, bus and I guess keyboard) with oscilloscope for clean signal.
5. Verified 33MHz present on ISA bus pin 30 (OSC)
6. Found no clock signal present on ISA bus pin 20 (CLK) with no boards in bus.
7. Touch-tested CPU and chipset chips all about as warm as expected.
8. Pulled AMIBIOS ColorBIOS 27C512 from socket and read it - seems OK so far as all ASCII data in the BIOS can be seen without errors.
I'm an 8-bit kind of guy and not too familiar with ISA hardware. What tests can I make to locate faults?
The motherboard has no jumper to enable/disable VLB video. Should I expect to see a VGA video BIOS message when trying a VGA card in the ISA bus?
I'm trying a Trident VLB video card based on TGUI9420, but with no docs found yet . Jumpers as follows:
1. Select STMB (two options of ARP/BRP configurations - are these on-board memory configs or upgrade option configs - there are a couple of unpopulated 40-pin SMC locations on the PCB?)
2. Select I or NI (is this interrupt/non-interrupt mode?)
3. Select +RAS on/off (what is this?)
4. Select Fast clock on/off
It would be nice to get a VLB video card working after all these years.
As to the motherboard, I'll only write it off if there are faults in the surface-mount UM chipset. Anthing socketed or minor discrete components I will try to replace, if I have a working board chipset.
Is there a standard procedure for this sort of trouble-shooting?
Rick
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