Recent content by terryfi

I agree. Apparently the screen on LCD models is kind of useless. Don't get me wrong I am really happy with the laptop the way it is. I am just surprised me that there is no info about the expansion cards on internet. Not a single mention of one of the cards or the technical specs.

Hi I got hold of a Data General One Model 2. Most Model 2s have LCD but mine has a electroluminescent screen which makes it very special. I would love add to its functionality by adding expansion cards e.g. EGA adapter or even sound cards. Unfortunately expansion slots use a proprietary...

Yes I didn't read all the message. You are right I need a 66 MHz oscillator for 386; the 33 MHz one came with mobo is only good for 486. The weird part is that chipset only regenerates the clock to get rid of skews and noise but does not provide frequency doubling in 386 mode. The chipset...

The clock I see on CPU CLK2 pin is 33 Mhz, there is no clock divider directly from chipset to CPU through some buffer/divider. I have to see what is happening internally in 386 cpu; external clock is 33Mhz. Maybe some initialization or fault in CPU. Last resort would be find another similar CPU...

Hi A while ago I acquired this 386/486 motherboard not posting described in this post https://forum.vcfed.org/index.php?threads/weird-short-on-386-486-motherboard.1244159/#post-1330446. I replaced the system chipset of the board and now it boots with a 486 DX 33 with no issue. However with a...

my multimeter sometimes is off up to 5 ohms so real value was probably <5ohms, regardless, when turned-off all AT motherboards I looked at have at least 100s of ohms resistance between 5V and GND. Motherboard alone (without any expansions) consumes less than 10 Watts when fully powered on. A...

Thanks everyone for your comments. modem7 by crystal I meant the system CLK oscillator next to slot 6. I looked at chipset datasheet below https://datasheet.datasheetarchive.com/originals/scans/Scans-067/DSA2IH00218654.pdf In system diagram it shows that clock is fed into a 74F224 octal buffer...

The short issue fixed after setting CPU in right orientaiton. CPU is still working fine in my other motherboard, the mobo chipset does not provide CLK to cpu I checked with scope. The crystal is ok, so it is issue with chipset or something required for chipset to generate clock.

As Twospruces suggested I checked orientation and it was wrong. But even right orientation didn't make the board post. When I checked CPU had no clock pulse. I looked at UM82C482AF system chipset and it receives right CLK_IN but there is no CLK_OUT does anyone have experience with UMC chipsets...

Thanks Twospruces, the silkscreen was for 387 the outer silkscreen for 486 was not easy to see, the manuals online all show another orientation!. checked ground pins with multimeter, confirmed then changed orientation and short is gone, although still not posting, more investigations ahead

Hi everyone, I recently pick up a non working 386/486 motherboard model Elitegroup US3486 FX3000. First attempt to turn it on, pico PSU did not power on due to a short on 5v rail. Multimeter confirmed short with <10 ohm resistance. When I remove the CPU however the short is gone and PSU turns...

PSU can output 5v up to 1.2A load; at 1.8A it will drop to 4.9V. I never heard 9VAC ever fails but will check that with multimeter later. My guess is that some chip has shorted overnight and VIC20 is now drawing so much current the PSU voltage drops significantly; other PSUs that works probably...

ofcourse it is the cost reduced I loadtest the PSU see if it goes overvoltage under high load

Hi everyone, I recently bought a VIC-20 and left it running overnight of course with the power supply of death! In morning, it was showing the garble screen and when I turned it off and on; the power led didn't turn on! I switched to another supply and it showed the garble screen below. I...

I found this reverse engineering of Comspec switcher board here: http://www.6502.org/users/sjgray/computer/pet40-80/index.html And its recreation here: http://www.6502.org/users/sjgray/projects/cbm4080/index.html I tried to find the jumper block in the schematic but it is not even mentioned in...