Tony Duell wrote:
>
> >
> > I need to double check a diagnostic I'm making. I have a board that fried
> > the a 1/2W ceramic resitor (in the -12V section of the PS). It also took
> > out a tant cap and the fuses for the +/- 12v (between the MB and the PS).
>
> Are you sure it wasn't just that the tants shorted and took out the
> resistor and fuses? I've had plenty of tantalum bead capacitors do that
> over the years.
Good news/bad news. Good news is that the 12v part of the system is work. Bad
news is that one of the 28F020's smoked.
> > I suspect the RS232 driver chips but I need to know if the ethernet nic
> > (aui & bnc) use -12v. Anyone?
>
> You're going to love this : Probably not, but it might do!
>
> The thing is that the AUI port, and the internal 10base2 transceiver need
> a 12V supply. But that supply can float with respect to the data lines
> (which are transformer-isolated anyway) and with respect to local ground.
Here is what I've been able to determine so far:
1) 5V section is fine.
2) -12V section has a major short (measured 0 ohms across it, not the
power supply).
3) The flash programming circuit has a problem.
4) The NIC seems to work as the hub now recognizes it but I haven't seen
what traffic is on it. Sniffer doesn't show a MAC address or anything.
But that may be the sniffer.
Conclusion/assumptions:
1) 5V is working, there for the main part of the mother board is unaffected.
2) Fails diags at LAN (7 error lights), may be SQE setting.
3) 28F020 fried but it's for D/L of image from tftp server.
4) -12v is only for RS232, there for short exists in that section.
Of course this is kind of weak right now.
BTW, the reason I asked the question here is that folks like us (real hackers)
tend to want to fix things and have the right kind of software/hardware
knowledge for this kind of stuff.
BTW(2), this is my $2 ebay find, a Nupon LTS-4 terminal server. When I fix it
I'll upgrade it to an 8 by adding the components. I should probably let it go
since I also have another terminal server on the way. But old electronics
shouldn't just be tossed in the trash, kind of feels wrong (yes I'm out of my
mind).
--
Linux Home Automation Neil Cherry ncherry_at_home.net
http://members.home.net/ncherry (Text only)
http://meltingpot.fortunecity.com/lightsey/52 (Graphics)
http://linuxha.sourceforge.net/ (SourceForge)
Received on Sun Aug 13 2000 - 12:26:11 BST