Cinematronics Monitor Help:
Here are a few tips that may help you if you are repopulating a Cinematronics Keltron monitor.
Click the images to enlarge them.
Where is D3 on the PCB and where is D8 on the schematic?
The 1N400x diode 'D3' (schematic pg. 2 at B5) is marked (silkscreened) on the PCB as 'D8'.
Voltage Regulator Good Practice:
There is no rectifier across 'IC8' (schematic pg. 2 at B2) as is good practice. Add one to the bottom of the PCB as shown here. The cathode goes to IC8 pin 1.
Where are C16 and C211?
The capacitor 'C16' (schematic pg. 2 at B5) and the capacitor 'C211' (schematic pg. 1 at C8) are not marked on the PCB but the holes are there. Some boards were populated without these two components. These capacitors provide a little power filtering close to IC201. They are not critical but a little more power filtering near a chip never hurts. I always replace or install these two parts while rebuilding one of these boards. I always replace the original tantalum parts with electrolytic parts.
Original parts:
New parts:
A commonly overlooked source of trouble comes from the resistors that are in-line (in series with) with the CRT socket wires. There are 4 of them. If you install new resistors, you'll need, as a minimum, 1/2 W parts that are rated for at least 400V maximum working voltage. If you can source parts rated for more than that, say 500V or 600V or higher, those would be better suited to this application. The resistance values are not critical so a 1% or 5% tolerance will be okay.
Wire color Socket pin # Resistor value Function Black 1 none heater Green 2 1 k G1 ground Red 3 47 k G2 400V Blue 4 47 k G4 ground (focus) White 5 none spark gap ground N.C. 6 none none Yellow 7 1 k cathode Brown 8 none heater The resistors are mechanically crimped to the wires and then covered with heatshrink tubing. The joints oxidize over time and the connections become intermittent. You must remove the heatshrink tubing. Just cut it with an X-acto knife or small side cutters. After removing the heatshrink tubing and if the existing resistor looks intact, then you can simply solder the crimps using rosin-core solder. Finally, cover the entire resistor and the joints with new heatshrink tubing.
If the resistor appears damaged in any way or if the resistors were overmolded with rubber (as some of them were), then simply clip the entire resistor section out of the wire, strip the wire ends back a few millimeters, and solder in new resistors. Cover the entire resistor and the joints with new heatshrink tubing.
Replacement Socket Wire Resistors:
It's nice to have a high voltage rating to avoid any remote possibility of flashover, however, the possibility of flashover actually occurring is remote. Consider that all of the socket wires, with the exception of the heater wires, are running into the CRT and into an electrode which is basically an open circuit. The cathode current is very tiny and doesn't cause much voltage drop. The red wire supplying the 400V grid is the worst case but again there's almost zero current. This means there's very little, if any, voltage drop across the resistors during normal operation. Since the voltage across them is so low, their actual working voltage is next to zero volts so they are not going to flash over unless something in the CRT actually shorts out. Even in that event, flashover is very unlikely because a short circuit would cause an excessive current draw that would sufficiently load down the power supply so as to reduce the voltage to a very low value. Adding a couple of layers of heatshrink tubing over the new resistors will increase the overall dielectric rating of the resistor to well beyond the minimum that is required for safety.
To be 100% safe and sure though, I like to install parts rated as high as possible, say 500V if I can find them. A small 1/2W 400V part will certainly suffice but I like to go higher. Also, I like to use 2W parts so that their physical size will make them more robust, after all, they are hanging by wires.
Generally, the larger a resistor is physically, the higher its maximum working voltage is. So, 1/2W parts tend to be rated 250V to 400V max. Some 1W parts and many 2W are often rated as 500V to 600V working voltage and 1000V maximum overload voltage.Here's my best picks of the Digikey parts:
Rated 500V, 2W, but it's not physically huge:
1 kohm: Yageo# FMP200JR-52-1K = Digikey# 1KZCT-ND
1 kohm:Vishay# PR02000201001JR500 = Digikey# PPC1.0KW-2CT-ND , Newark# 94C2424
47 kohm: Yageo: FMP200JR-52-47K = Digikey# 47KZCT-ND
47 kohm: Vishay# PR02000204702JR500 = Digikey# PPC47KW-2CT-ND , Newark# 94C2520
Regarding the original crimps:
You don't need them. Don't worry about installing new crimps. They were used originally by the factory machine that connected the resistors to the wires to eliminate a more costly soldering process. If you really want to, you can bend each new resistor lead into small loop and stick the wire through the loop and bend it around so that they are hooked together, then solder the joint. I prefer to just lay the resistor lead and wire side-by-side together and solder a 1/4" length. I then slide heakshrink tubing over the entire resistor and the connections and shrink it.
Replacement Heatshrink Tubing:
I specifically use the glue-filled heatshrink tubing because it has a thicker wall and it will actually hold everything together because of the glue inside. I usually apply two layers just to build up the stiffness and strength of the resistor-wire assembly so that there's little tendency to bend at the joints.
Qualtek # Q5-3X-3/16-01-QB48IN-25 = $1.52 per 4' length, black, 3-to-1 shrinkage, 4.8mm inner diameter =
Digikey # Q53X316B-ND
My experience with Cinematronic monitors has shown me that oftentimes when a monitor lands on my bench, it is missing the small transistor heatsinks. The heatsinks are critical to the survival of the transistors. I have seen some boards with the wrong heatsink installed or none at all. It is imperetive that the heatsinks be installed with a small amount of white thermal grease. The correct replacement for the original heatsink is
Aavid Thermalloy # 323005B00000G, Digikey# HS101-ND
Another problem that I've noticed is that two of the transistors, specifically Q105 and Q205 tend to run very hot. These two transistors were not equipped with heatsinks from the factory, but I highly recommend that you install heatsinks on them just to allow them to run a little cooler and hopefully last a lot longer. Because there are other components (resistors and diodes) very close to Q105 and Q205, heatsinks of the original style will not fit, however, the new heatsink style shown below will fit perfectly.
Aavid Thermalloy # 322505B00000G, Digikey# HS242-ND
Installed at Q105:
Installed at Q205:
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