I got the datasheet of 486DX100 from AMD site. It is a 208 pin SQFP surface mounted to the PCB. So not easy to swap. I tried to probe around, Reset (pin48) is high (OK), SRESET(pin 58) is high (OK), didn't get to test all VCC but measured quite well at 3.3V for those I probed. It is tough to probe correctly as pins are very close to each other. Clock has waveform coming in. A0 and D0 have NO activities, no activities to all the few other high order data-bits and address-bits (didn't tried all). I think the first beep must be generated differently otherwise I should have a beep if there is power coming in. Also confirm it is not Bios fault as I have a good one to swap. DRAM also is good. No have much LEDs to see as I removed all peripherals, KB LEDs did flash on power on, but pressing num-lock or cap-lock did not change LED status. So far under my cheapo magnifying glass, no burnt part is found yet. I hate to think it is CPU, because it is a lot of jobs to verify-- how to take out, and where to find a replacement 486DX100 and how to solder back. Any other easier faults to look for? Cheers, Ling SM >Sometimes there's a second "Startup" battery, but more often a CMOS on-switch circuit uses the RT Clock battery to switch the laptop's power on (or toggle power), from a SPST switch. This way just the one CMOS IC is "always on", and you can still . Horrid ASCII circuit of one version of a toggler, tap the button and power toggles on or off: +--------R-------+ | | | --- |\ | |\ +---+--o o--+--| >O--+--| >O---+-- OUT | Button | |/ |/ | | (N.O.) | | --- +-------R----------+ --- C | GND (There was a Dave Johnson thread about this sort of toggle circuit in early 1999 ) If the CPU is warm and the HDD is spinning, then this isn't it, as you'd just get No Power-up if this was the culprit. If the HDD is spinning, you do have power No idea if the BIOS is good / bad as no display, of course. No external VGA and no screen is a bad sign. No beep, though, means (as Bruce and Richard say) probably ~PwrGood isn't going low - so a power supply problem. A corrupt BIOS or a bad CPU, are possible causes as well. (Hoping someone didn't yank and re-install the CPU turned 90 or 180 degrees - That's not pretty!) These debugging situations are always easier in person, of course. Are any LED's flashing / changing color, or Floppy or HDD LEDs flashing at all? Probably not as no single beep. Cannot plug a POST code reader card in as this is a laptop. I think I'd suggest disassembly followed by physical examination for blown chips / transistors, then go for a CPU swap if it's a socketed CPU (see if it'll work on a desktop motherboard) and then verify that the Flash or EPRom is good (Is the BIOS socketed, and is it a ROM, EEProm, or Flash device?) Hoping this isn't a virus-reflashed BIOS chip, well, there are enough of us on list that can re-program ROM variants that if it's the ROM you should be able to get that fixed. Mark V sml wrote: > Thanks Andrew & Mark. Sorry to take so long to response, as usual > distracted by work. Back to the fun stuff. > > Cable is OK, power is OK I think as the CPU is warm and hard disk is > hissing, no burn trace. Mark, I thought the battery is for clock & > cmos and got nothing to do with startup. Please enlighten more. > > CPU is hot, no beep, no external VGA, never get to the beep state also > I think. I How likely is it be the CPU (AMD chip) fault? > > Cheers, Ling SM > > Mark: > >No Display - does this mean it seems to boot, beep normally, access > the > HDD and FDD normally, but nothing output onto the display? Sometimes > that means the backlight's dead, sometimes the display cable as Andy > mentions, also check the cable for integrity (If it's cracked it isn't > going to work!) > > >If it doesn't boot normally; Check the power MOSFET's in the > laptop's > PSU - I find bad solder joints in those quite often cause a "No Boot" > problem. Temperature cycling (I guess) causes these to eventually go > bad. And, if you haven't already, see if the Lithium Coin Cell type > battery in the startup circuit is being a 'problem child' due to being > dead of old age (Compaq LTE 386/25's are GOOD at not starting, due to > this - I've been given quite a few that only had THIS as a problem, > replace the batt. and it starts.) The other thing to look for is > loose > screws inside the laptop (I've seen a few, trace repair is always "SO > Much FUN", as we all know!) > > Worst case older laptops aren't that expensive to replace, local > places > have them for cheap rather often. > > From: Andrew Kunz > > I've usually found the cable from the chip on the motherboard to the > display in > the lid to be the problem. Bad connectors, cable pulled from > connector, etc. > > It's a lot easier to repair than a chip! > > Also, make sure the external VGA works first. > > Ling > >Need to repair my brother's laptop (I know it does not worth, but he > can't part with it). No display, I have check for the simple faults > but no luck. Guess, i would have to trace the VGA graphics chips, > etc. Are there sites with more detail information and maybe with some > circuit diagrams? > > Anyone knows of a good PC repair site? I have comb through several > search engines, but sites found have not been good. -- Detest spam? 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