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5160 wont start, mobo problem?

channelmaniac said:
It takes copper traces to go from one cap to the next and those traces have very tiny, but measurable resistance values. When you get to the shorted cap you'll find a lower resistance value. Remove that cap and you should have the short circuit gone.

RJ
Click to expand...

Yes, it was a shorted cap on my 5170's disk controller that prevented any sign of life. With that replaced, volia! It rose Lazarus-like from the dead. See
http://www.classic-computers.org.nz...ng an-IBM-AT--diagnosing a PSU non-start.html

Tez
 
tezza said:
Yes, it was a shorted cap on my 5170's disk controller that prevented any sign of life. With that replaced, volia! It rose Lazarus-like from the dead. See
http://www.classic-computers.org.nz...ng an-IBM-AT--diagnosing a PSU non-start.html

Tez
Click to expand...

Exactly!

But if you have dozens of the caps it's tough to find the bad one without desoldering an end off each until you find the bad one. If you use the ESR meter, you'll find an area of caps that have lower resistance than others (.05 ohms vs .01 ohms).. when you find the lowest with that ESR meter then desolder it and you'll have the bad one quickly isolated. ;)
 
If you're handy, you can build one of the many do-it-yourself milliohmmeters on the web. Most are 4-wire (Kelvin bridge) setups using op amps and simple to build. Rich Cappels has a rather clever circuit using 1KHz bursts of low-level AC.
 
IMO it's not hard to find the broken one - give it an ampere or two with a regulated power supply, and the capacitor will budge. Safety glasses recommended though.
 
channelmaniac said:
Everyone that troubleshoots shorted capacitors should have one of these:

http://www.anatekcorp.com/blueesr.htm

The ESR meter is nothing more than a high frequency milliohm meter that will go down to a hundredth of an ohm: .01 ohm. By doing this you can measure the caps to find the one with the lowest resistance to find the one that is shorted.

It takes copper traces to go from one cap to the next and those traces have very tiny, but measurable resistance values. When you get to the shorted cap you'll find a lower resistance value. Remove that cap and you should have the short circuit gone.

RJ
Click to expand...

I have a Capacitor Wizard which is a similar device. The problem with using it for this is that tantalum capacitors have very low ESR, that's one of their advantages, so a good one will often appear shorted to an ESR meter.

Most multimeters are not precise enough to measure very low resistances. A milliohm meter with good quality probes can do it but even then it's not 100%. Even a shorted component will still have *some* resistance, and if the adjacent parts are nearby and on big fat traces or power/ground planes it can still be tough to locate. Worth a shot though.
 
If you've got a well-stocked hellbox, a simple milliohmmeter can be constructed with an LM317 voltage regulator and a few odds and ends.

But if it were my board, I'd just start with the capacitors closest to the power connector and work out from there.
 
Ok, have been busy for a while, but have started testing the mobo, could not find the problem so I switched the mobo with a working one from a 5155.
Computer starts up, single beep, floppy seek, harddisc spins up and starts reading, but nothing on screen, screens stays black. Switched the 5154 for a 5151 screen, adjusted the brightnes to full, and all I can see are horizontal lines. plugged in the CGA adapter from my 5155 (is working), the same, only horizontal lines, tried the graphics adapter from my 5170 with the monitor from my 5170, again horizontal lines, but this time with a blinking cursor. Tried all possible switch settings (5 and 6) but no luck. Switched Bios roms with latest version, same problem. Mobo is working, so are the adapters from my 5155 and 5170, the computers boots up, with single beep, so no errors, floppy seek, HD seek. What else can there be wrong, or what else can I try?
 
Did you adjust the dip switches on the motherboard to correspond with the new graphics card?

Be careful, you might damage the card or monitor by plugging the incorrect one into it..

xtdips.gif
 
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