A3000: Amber’s Variable Resistor

AmberSyncThe A3000 was randomly deciding to output a proper signal to VGA. I know the monitor I was using (or LCD) was capable of displaying in the right frequency range — but only 1 out 5 power ups would yield an active VGA display.

It was easy to tell when a good powerup would occur, as the VGA display would have some very dark gray vertical lines in the black screen.

Putting a scope on the VGA port showed signals on the RGB and H/V sync pins. Each signal looked okay from a casual inspection (comparing a good powerup versus bad). I checked all the pins around the board to see if there was anything missing on the way in to the VGA… but if the VGA signals looked ok either way (on or off) then it must be a very slight signal variance.

The variable resistor on Amber was very touchy. I had a spare that would work, but I re-soldered the old part just to be sure.. it looked like there had been some work previously done on it. Using a metal screwdriver, I noticed the signals jumping around on the V/H pins. Removing the screwdriver would change the signal as well. I had a plastic screwdriver for altering TBC signals — TBC’s did the same thing with metal tools.

Without worrying about over turning the resistor, I swung it pretty far. I then noticed it was loose. After screwing it down for a while, I felt a bump and then the signal seemed to tune easier. I found the sweet spot, rebooted — VGA stable. I waited 30 minutes with the machine off tried again, still good. Off for two days, powered it up — still working fine. Nailed it 🙂

A3000 Clock Spagetti

clockspagettiThe A3000 I am working on has a few issues, the first was NO CLOCK reported by SYSINFO and other tools. This is of course true, as the battery had been removed after I unboxed this machine. After the battery was removed, the gross damage to the motherboard by the leaking battery is obvious in the picture to the left.

I cleaned the board as best I could, noticed that the back of the board was OK… somehow. I didn’t want to mess with the area around where the battery was, as there was a lot of damage there and I didn’t want to add to it.

I temporarily jumped a CR2032 in a holder (the BLACK and RED leads),  to get get the clock powered. I then went into the Prefs and set the time. After a reboot, the system recognized the clock — but the time had not incremented while the machine was off.

The clock crystal was not outputting anything which ended up being a connection from C192 to R193 was lost. I jumpered them with the BLUE lead. After checking all the connections out I found C190 was not connected either, so i jumpered it with the YELLOW lead.

clocksignalAs opposed to a flatlined output from the Oscillator, I got a signal.

I loaded up the system, reset the time powered it off and waited a few minutes. Turned it back on and the time was in sync. I went out for dinner, had a few drinks and came back — powered it up, clock still working.

I know the clock is not so important in this day and age, as NTP can handle the time sync. But who wants a broken machine?

Next on the list.. Display warm up… sometimes the display shows something, sometimes it takes a few power cycles to get it going…

A3000T: New friend :) Mouse and Keyboard :(

Well, I’ve got 2 Amiga 3000’s going, which means they are in 30 pieces on my workbench.

One is a A3000D, with 2MB/16MB/256MB of various RAM types. I’ve managed to get the latest custom chips on the mother board, all but a Super DMAC04. This machine has been in the basement for a while, with battery damage and a few blown caps. It now boots with 3.1 KS and 3.9 OS. The VGA port takes a little while to warm up, the machine needs to be on for about 2 minutes and then power cycled to get VGA back up. Working out the VGA is the next major task…

Number Two, is an A3000T. I can’t think of a heavier computer. This one booted right off the bat, but for some reason the mouse and keyboard wasn’t working. Scouring the motherboard for bad components/traces, reading forums and voltmeter came up empty. I could understand why one port would go or just the keyboard… but all three ports? The system would boot to a temp OS disk I mounted, but as soon as the OS was up (or even the KS screen) not keyboard or mouse action. Weird. Even the 3 finger salute on the KS screen..

There is something to be said for computers with a keyhole embedded in its face plate. Yes, when in the locked position — no keyboard or mouse. Funny… I have never had this happen in the last 30 years. The trick that works on old bike locks (Plastic Bik pens, cut in particular way) works on the lock in A3000T. I can see that the lock has been man handled before. When I opened the lock, everything started working.

This machine needs a lot of TLC. The case wasn’t intact, missing the front and top sections. It also has older chips than my A3000D. I was kind of hoping this one was going to have a late revision Super DMAC… oh well 🙂