mab@druhi.ATT.COM (A.Bland) (02/23/88)
A little bit of user port hacking over the weekend has left my C128 dead. I know, never give a soldering iron to a software jock, but... I seem to have accidently shorted user port pins 10 and 11 (both are labeled 9VAC). Pins C-L (data) and N (GND) were also connected at the time, but I don't suspect that they caused any problems. The C128 booted OK at first, but when I tried to type on the keyboard, nothing happened. The 80-column cursor was still flashing, however, so I thought the machine was still somewhat healthy. After powering down and removing my junk from the user port, I can no longer get the C128 to power up. The power LED lights up, but nothing else happens (40 and 80 column screens stay blank, disk drive doesn't boot). I tried swapping the two CIA chips, suspecting that I had fried one of them, but that didn't change anything. I can't find a fuse anywhere, so I guess it's not a blown fuse. My next guess is that I may have done something nasty to the power supply, but I don't know how to verify that. Any suggestions before I make a trip to a repair center would be greatly appreciated. I'm anxious to get the machine working again so I can get back to my user port hacking :-) Thanks! -- Alan Bland AT&T Denver ihnp4!druhi!mab
mclek@dcatla.UUCP (Larry E. Kollar) (02/23/88)
In article <2706@druhi.ATT.COM> mab@druhi.ATT.COM (A.Bland) writes: >A little bit of user port hacking over the weekend has left my C128 dead. > >I seem to have accidently shorted user port pins 10 and 11 (both are >labeled 9VAC). Pins C-L (data) and N (GND) were also connected at the >time, but I don't suspect that they caused any problems. > >I tried swapping the two CIA chips, suspecting that I had fried one of >them, but that didn't change anything. A friend of mine did something similar when he pulled his modem out of a live C128. We had a busted 64 sitting around, so we pulled the CIA out of that board & put it on the 128. No luck, so off to the repair shop. Turned out that not only the CIA was fried, but several other chips as well. The repair bill came to about $80. And this is from a person who tries to save his customers money (he told us that a couple of other chips were in a position to be "weakened" from the voltage spike, and that he would replace them for parts cost only if they failed within a month). I'm sorry that I couldn't give a more optimistic reply. Perhaps the market exists for a user port buffer which would allow you to abuse it w/o destroying chips. Larry Kollar ...!gatech!dcatla!mclek "Little guy, little hands, little eyes and lots of time, What you gonna be, what you gonna see, when your eyes are level with mine?"
prindle@NADC.ARPA (Frank Prindle) (02/24/88)
Shorting the two 9V pins on the user port directly shorts the 9 Volt AC output from the external power supply. The only components in the path are two small RF chokes near the power connector and the power switch itself - it is possible that one of those is fried, or that you melted a trace on the PC board; Or the power supply might have blown a fuse. To check the power supply, measure between DIN connector pins 3 and 5 (on the square-ish plug that comes from the supply) for 9 to 15 volts AC, and between pins 1 and 4 on the same plug for 5 volts DC (pin 1 positive). If either voltage is missing, the 128 cannot function properly. One fuse on the C128 supply is externally accessible from the bottom of the supply (you'd be amazed how many people never turned the sucker over!). I'm not sure if the same fuse protects both outputs, or if there is another fuse inside for the AC output. The C64 had a fuse for the 9 VAC lines *inside* the C64, but the C128 schematic doesn't show any (that doesn't mean there isn't one)! Sincerely, Frank Prindle Prindle@NADC.arpa
Brendan@cup.portal.com (02/24/88)
That sounds a little like something that happened to me..my little brother,
in his endless helpful way, plugged the modem into the user port, UPSIDE DOWN,
and the computer seemed deader than a doornail..I panicked & sent it off
to a repair shop, and found out for my $80 repair job all they had to do
is replace a fuse in the power supply...it seems that one of them blows
if you short out the user port...I forget the specific value right now,
but it says it right on one of the metal ends of the fuse..assuming your
warrantee's expired, open up your power supply and make sure neither
of the fuses have blown..if one has, then voila, end of problem..
Hope I've helped,
Brendan Kehoe
UUCP: ...sun!portal!cup.portal.com!Brendan_Patrick_Kehoe
Portal: Brendanelg@killer.UUCP (Eric Green) (02/25/88)
in article <2706@druhi.ATT.COM>, mab@druhi.ATT.COM (A.Bland) says: > I seem to have accidently shorted user port pins 10 and 11 (both are > labeled 9VAC). Pins C-L (data) and N (GND) were also connected at the > time, but I don't suspect that they caused any problems. If you shorted the 9VAC, you almost certainly blew the 9vAC fuse. I don't know where that fuse is in a C128... maybe it's the one that's in the bottom of your power supply. Take a look, it's right there on the bottom of your power supply. > OK at first, but when I tried to type on the keyboard, nothing happened. > The 80-column cursor was still flashing, however, so I thought the machine > was still somewhat healthy. 80 column chip isn't powered by the 9VAC power supply. However, the VIC][ chip is. Since the VIC][ chip also happens to generate all system timing..... note -- I don't know if the C128's VIC][ still uses the 9VAC (I've blown the 9VAC fuse in my 64 a number of times -- I don't subject my 128 to my hardware projects). Because the 80column cursor is in hardware, it naturally kept flashing, because the 80column hardware had already been initialized. As for CIA's: You might want to lay on a spare. $8.95 from Jameco Electronics, I believe. Since min. order is $20, you might want to grab a spare CPU or something, too (they stock all the Commodore chips for the aspiring Commodore hacker to put his machine back together with :-). Orders 415-592-8097, info 415-592-8121. -- Eric Lee Green elg@usl.CSNET Asimov Cocktail,n., A verbal bomb {cbosgd,ihnp4}!killer!elg detonated by the mention of any Snail Mail P.O. Box 92191 subject, resulting in an explosion Lafayette, LA 70509 of at least 5,000 words.
mab@druhi.ATT.COM (A.Bland) (02/27/88)
In article <3484@killer.UUCP>, elg@killer.UUCP (Eric Green) writes: > If you shorted the 9VAC, you almost certainly blew the 9vAC fuse. I don't know > where that fuse is in a C128... maybe it's the one that's in the bottom of > your power supply. Take a look, it's right there on the bottom of your power > supply. Yes, indeed, it was the 9VAC fuse. I had originally suspected it was a blown fuse, but I couldn't find any fuses anywhere. Not even on the bottom of my power supply! Unlike Eric's and Frank Prindle's power supplies, mine has both of its fuses on the inside. No fuses are visible externally, and I never thought to check inside the power supply before now. Many thanks to everyone who responded. All systems are go, and as soon as I finish this posting, I'm removing the modem from the user port so I can get back to where I left off last weekend! And I even have a spare fuse now :-) -- Alan Bland AT&T Denver ihnp4!druhi!mab
elg@killer.UUCP (Eric Green) (02/27/88)
in article <3448@cup.portal.com>, Brendan@cup.portal.com says: > That sounds a little like something that happened to me..my little brother, > in his endless helpful way, plugged the modem into the user port, UPSIDE DOWN, > and the computer seemed deader than a doornail.. I did that once to my 64, with an Anchor Volksmodem 1200. Fried just about every chip in the computer. I figure that the 9vac got routed into the innards. Got rid of the Anchor, ended up replacing every RAM chip, the CIA's, one of the ROMs, the CPU, the PLA, the VIC ][.... that was an EXPENSIVE mistake. However, just shorting together the 9vac ought to blow a fuse somewhere, and should not cause any permenant damage to the computer. -- Eric Lee Green elg@usl.CSNET Asimov Cocktail,n., A verbal bomb {cbosgd,ihnp4}!killer!elg detonated by the mention of any Snail Mail P.O. Box 92191 subject, resulting in an explosion Lafayette, LA 70509 of at least 5,000 words.