Refurbishing a Classic Monitor (Page 3)|
By, William Stephens
Although this Toei monitor looks to have not run for very long, I will still reflow some key points on the circuitboard. First is the flyback transformer and Next and Last are any pinouts on the board like the yoke, power, signal and degauss connectors. Reflowing is a simple 2 step process: 1 Remove the solder using a solder sucker or solder wick. 2 Re-solder the connection with fresh new solder. Make sure that no mating connectors are attached to the pins on the circuit board. The soldering heat can damage the mating connectors.
It is not likely that heat stress or vibration microcracks have formed on this particular monitor, but ones that have operated for a while will develop these flaws in the solder joints which causes a whole host of problems. Some solder and a couple minutes time can save many problems down the line. I decided to reflow the usual suspects on the Toei anyway although it most probably does not need it... once again, one of those nasty habits I have developed.
Now, we can get down to the nitty-gritty of the job, putting in the new capacitors. Open up the capkit and group your capacitors any way you want. It seems that no matter what type of pre-organization I use, it gets all messed up through the process of flipping the main board assembly over and over to locate, unsolder, re-insert and solder. I do the caps one type at a time. Most cap kits usually start off with the 1uf 50v cap(s), the Toei is no different and in this case it's C27. On many monitors, the reference designators for the parts are silk screened on both sides of the pc board, sometimes it's not. The Toei has part designators marked on the component side of the board only. You basically need to hunt around the pc board until you find the reference designation... this can be difficult, just be patient and don't drink too much coffee.
Once you have located the part in question, flip the board over and solder suck or wick the connections clean of solder. The part should come loose with a tiny bit of rocking, if it's a bit stubborn, re-heat the connection and lightly pull the part out of the hole. You should be careful here because in rocking the part, if it's not nearly detached or detached it can pull the copper pad and attached traces up off the circuit board.
Some caution should be observed when changing out capacitors. Some pc boards have incorrect markings so it is best to observe carefully the orientation of the old part as you extract it in order to replace the capacitor with the right leads going into the correct holes. If you get this wrong, the capacitor will probably blow, taking some other components with it.
With the part oriented correctly in the holes, solder the leads to the circuit traces. Once soldered, cut off the excess lead(s) while holding them so they don't get stuck somewhere in the chassis.
The one really nice thing about monitor circuit boards is that they only have circuit traces on one side of the board. This makes unsoldering components a breeze. I use solderwick to remove the solder, and once the solder has been wicked from the component leads, the part generally falls right out of the holes. This never happens with multilayer pc boards.
Repeat this process for each capacitor in the kit and before you know it, you're done!
Now that you are done, you should have a pile of old capacitors and the clipped leads left. Throw these away, you really should never consider using them again. Make sure to get rid of the clipped leads. I could tell you horror stories of one of those things getting stuck in a chassis right under the flyback transformer... "Pop!! Bang!!".
We're almost at the finish line, it's time to re-assemble the monitor and hook it back up to see what all our hard work has accomplished. Take your time and make sure everything you disconnected is connected again. The checklist for this article is the ground wire to the neck board, the neck board to the CRT, the yoke plug, the degauss plug and the good old CRT anode wire. Just to exude confidence, go ahead and screw the chassis back in. You won't need to take it back out for some reason, right?
Hook up you video source and isolated AC power source and flip the switch! You should hear some high voltage sizzle as the tube charges up and in a few seconds, your screen should light up.
With our Toei test subject, the capkit installation was a raging success. I was able to re center the controls and finally I got some vertical lock out of the monitor. All the waviness and jitter are gone and the monitor even comes up faster. That's not bad for less than $8 in parts and few hours.
Although I did use a CRT tester/rejuvenator and a pattern generator, you can do this job without these things. All that's required was a cap kit, a couple screwdrivers, some clip leads, a soldering iron, wire cutters, solder and solderwick or a solder sucker. What was curiously missing were multimeters, oscilloscopes, or any of the many electronics tools as well as the schematic diagram. As I said, they are all just like "peas in a pod", knowing one is like knowing them all.