REPAIRING YOUR COMMODORE MONITOR
                Latest updates and/or corrrections 4-14-2012

Commodore monitors fail most often due to poor solder connections. I've repaired 
quite a few of them and have been asked by owners if they can do the job themselves 
since shipping a monitor carries a significant risk of damage as well as being 
rather expensive. For those who are handy with a soldering iron, this article is 
intended to provide information necessary for the user to do their own repairs.
     Problems related to poor solder show diverse symptoms such as intermittent 
picture, or the monitor failing to come on when cold... or failing after warmup. 
Sometimes bumping the monitor with your hand will cause it to fail, or to start 
working again. Such intermittents are typical of poor PC board connections. 
     Note that this article was written using a 1084/1902A monitor as a model. 
Therefore, some variation will be noted with other Commodore monitors.

HIGH VOLTAGE WARNING: Note the red wire that goes from the high voltage transformer 
up to the picture tube cap. Under that cap is the high voltage connection to the 
picture tube. Even with the monitor turned off and unplugged, the tube can still
hold a charge. To discharge it safely, it's necessary to connect a wire from the
black coating on the tube or to chassis metal, then to the connector under the cap 
of the tube. I can do that with two screwdrivers, but a wire with a firm ground 
connection is safer. One end of that wire needs to be slipped under the cup until
it touches the connector underneath. You may hear a snap as it makes connection. 
Leave it connected for several minutes to make sure the tube is fully discharged!
Then it's safe to remove the cap from the tube. Lift up one edge of the cap and
observe the spring-wire connector that holds it in place. Pushing the cap to the 
side will allow one end of the spring clip to pop up and out of the connector. 
Never use excessive force or try to pry it out! 

DISASSEMBLY
     Lay the monitor face down on a protective cloth to prevent scratches to the
cabinet. The rear cover is usually held on with 4 or 5 screws. The ones at the case 
top are recessed, so a long blade Philips screwdriver is necessary to remove them. 
One more small screw near the rear panel connector is sometimes used and also needs 
to be removed. As the rear cover is pulled up and off, the speaker cable connector 
must be detached from the chassis inside. Don't hit the CRT board!
     Most monitors have three separate circuit boards. The bottom, main board is 
where most of the work needs to be done. The power supply board should also be
checked for poor solder as well as the CRT board attached to the neck of the 
picture tube. The main and PS boards will both slide rearward and as you do so, 
notice the connectors that must be disconnected to free the chassis from the
cabinet. Start with the PS board. Note the two silver braids that are soldered 
to that board. One goes to the CRT board and the other to the main chassis metal
shield on the bottom. Unsolder the one from the chassis bottom and the other 
from the PS board. Unplug the connectors, then press in on the tab (there is a 
square hole in the case bottom) and pull out the PS assembly. Unplug the CRT board 
from the tube by grasping it at its edges and gently pulling it rearward and 
rocking (NOT twisting!) it slightly until it unplugs from the tube. Set the monitor 
upright on the table and slide the main board rearward until you can get to the 
connectors on it, unplug them, and remove the main chassis. Make notes as you go 
so you'll know where all the connectors go back, or put paper tags on them marked 
with the necessary information. 

MAIN BOARD BOTTOM, METAL SHIELD REMOVAL

     Removing the metal shield from the bottom of the main board is perhaps the 
toughest part of this work. It is soldered all the way around its perimeter and must 
be unsoldered intact without damaging the copper board traces underneath. The best
way to do that is to set the board on edge and work at each solder point to free 
it up, then move to the next one. Having the board on edge allows any excess solder
to drop onto the table (which should have a protective covering, by the way) rather 
than onto the board. Solder splashes are to be avoided. Such a short anywhere on the 
board can be disasterous. There are a few places on the board edge where the shield 
is soldered along several inches of board copper. With the board on edge, I start at 
the top and heat the metal with a larger iron tip than normal so the solder flows 
downward, and as I heat it, separate the metal from the board... gently! It's often
necessary to run the iron back and forth over the same spots to ensure they are 
free. Once the shield is off of the board, clean it up to facilitate putting it back 
once the PC board resoldering is done. Repair any traces lifted during the shield 
removal process, if necessary. Be very careful you don't damage any of the controls 
because their shafts stick way out of the board front and thus are vulnerable. 

PC BOARD RESOLDERING

     The main areas of interest are the high voltage transformer (also called a 
"flyback" or "line output transformer" LOPT), the small H driver transformer, all 
power transistors and diodes, and any resistor of 1 Watt or more. The connections to 
the leads of the flyback often break loose from the board, and if you look carefully, 
you may see tiny cracks in the solder around those leads. That is the source of
the problem and it is corrected by resoldering -all- the leads, even the ones that 
look OK, since the connections could be loose underneath the solder where you can't 
see it. Always use fresh solder (I use 60:40 rosin core radio solder) to do this 
rework. Never try to just reflow the old solder... it will not hold up. The rosin 
in the new solder will completely reflow and secure the connection. 
     Examine the board under strong light to see if there are any solder bridges 
or areas that need rework. Changing the lighting often helps to find areas that 
were missed before. If there are any cracks in the circuit boards, those need to 
be repaired by lining the broken edges together, if necessary, and putting a few 
small drops of super glue on the crack and allowing it to wick it's way into the 
breaks. After the glue dries (give it at least an hour), the broken copper traces 
can be repaired by scraping the copper clean on both sides of the break so it's 
shiny, and then bridging the break with wire soldered to both sides. I use a single 
strand pulled out of a piece of stranded hookup wire for my rework. The strand is 
very thin and works well, especially if there are several broken traces side by 
side. If so, it helps to stagger the solder points away from each other so they 
don't overlap. Use a very small soldering iron tip for that work. 

REASSEMBLY

     The bottom metal shield can now be reattached. Make sure before soldering 
that all tabs fit in their respective holes and no part of the shield shorts to 
any part of the PC board. Reinstalling the chassis should be straightforward. 
All the connectors are keyed so they can't be installed backwards. Hopefully 
you made notes as to where they all went. Don't forget the speaker connection 
as you're putting the rear cover back on. I've done that more times than I care
to admit. After resoldering, your Commodore monitor will be much more reliable 
from then on.

Ray Carlsen
CARLSEN ELECTRONICS