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TRS-80 Model 4P Power Switch Light

J

jmetal88

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Jul 23, 2010
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Location
Derby, KS
I had my Model 4P apart today to work on the power supply (I had an ATX power supply board ready to go if need be, but the only problem turned out to be a few cracked solder joints and re-flowing them fixed the shrinking/blooming screen problem I was having quite nicely), and while I was at it, I decided to take the front bezel off and check out the power switch, as the light bulb inside apparently burned out sometime before I picked up the machine.

A few problems: One, the power switch looks to be sealed to me, so I'm not sure I can change the bulb without changing the switch. I haven't been able to get too close a look, so if I'm wrong about that, let me know. Two, no matter how hard I tried I was not able to force the panel clips in far enough to actually remove the power switch, and I'm afraid I will have to break them to actually be able to get it out. Three, I haven't been able to find a suitable replacement switch yet (one that's illuminated, has a V-shaped rocker, the correct dimensions, and five terminals instead of four or six), and I'd really want to know where I can get one before I try any harder to force the switch out of its panel.

So, does anyone here know where to find the correct switch for these, and does anyone have any advice for actually removing the original switch without damaging it?
 
The original lit switch (at least in mine) was an OSLO Switch RTL11A125VIC9.

http://www.osloswitch.com/files/2914/3015/1465/full-size-lighted-tech-sheet-double-pole.pdf

You shouldn't have any problem finding a similar switch from most electronics suppliers.

The only thing critical is that the switch you put in is a double pole switch (both hot and neutral switched). The original switch had 5 leads - one was to provide ground (neutral) to the lamp. Some 4 lead switches have the lamp internally connected across the two poles in which case the spare neutral would not be used.
Some lit switches have isolated lamp contacts (6 leads) which you would have to bridge one side to the common.
Neon lights typically last about 20 to 25 years, and this switch is now available with an LED.


Howard
 
With mine I first removed the front black plastic housing that holds the switches and controls. I was able to remove the switch without too much trouble. I used a generic 4 terminal switch (similar to the Oslo 111 circuit instead of the 11 - see data sheet). This type is readily available in many colors. I simply reconnected the leads as original and left the 5th one off (capped with heatshrink).
 
If you just want to change the bulb, it's pretty straightforward to open the switch. See where the rocker has protrusions into the outer casing to serve as pivots? That's what holds the switch together. Just insert a small flat-bladed screwdriver between the rocker and the outer housing to pry away the housing so the rocker pivot is free. Do the same on the other side and the rocker will come right out. Be sure to catch any parts that fall out--usually there are a couple of contacts and springs. Replace the lamp (usually a miniature NE2H with a resistor in series), carefully reassemble the switch parts and, using the small screwdriver if needed, push the rocker home.

I've done lots of these and it's pretty easy. Just don't let the small parts get away!
 
Chuck(G) said:
If you just want to change the bulb, it's pretty straightforward to open the switch. See where the rocker has protrusions into the outer casing to serve as pivots? That's what holds the switch together. Just insert a small flat-bladed screwdriver between the rocker and the outer housing to pry away the housing so the rocker pivot is free. Do the same on the other side and the rocker will come right out. Be sure to catch any parts that fall out--usually there are a couple of contacts and springs. Replace the lamp (usually a miniature NE2H with a resistor in series), carefully reassemble the switch parts and, using the small screwdriver if needed, push the rocker home.

I've done lots of these and it's pretty easy. Just don't let the small parts get away!
Click to expand...

This is what I'd like to do, ideally, but for whatever reason I just cannot force the panel clips in far enough to actually remove the switch from the panel. I can get it popped out about 2mm, but then when I try to force it any farther, one of the sides usually just pops back into place.
 
Try something like a pair of Channelocks or maybe a gluing clamp to bring those tabs in. Or try compressing one side far enough to allow you to slide that part of the switch out a bit, then do the same for the other side. The switch went in--it's got to come out.
 
Chuck(G) said:
Try something like a pair of Channelocks or maybe a gluing clamp to bring those tabs in. Or try compressing one side far enough to allow you to slide that part of the switch out a bit, then do the same for the other side. The switch went in--it's got to come out.
Click to expand...

Okay, I got it. Had to switch to a much bigger screwdriver to be able to force one of the sides down that much, though. Now I'll see if I can get it apart.
 
Well, turns out the bulb wasn't burnt out after all, the lead had just broken off inside the switch. It was right at the base of the bulb so it was hard to solder back together, but I got it connected with a short piece of wrapping wire. The switch lights up now!
 
Well, short-lived success there, I guess one of the capacitors in my power supply was about dead, because the system just released a large amount of smoke and started making continuous popping noises. Looks like it was one of the AC filter capacitors. I think I'd still prefer to use the original power supply rather than hacking in an ATX power supply, so I'll just look into replacing the capacitor (although the system was still operating when it popped so I might be able to use it without the capacitor temporarily anyway).
 
And, we're back to working again. The 0.22 uF film capacitor is the one that blew up, but the 0.01 uF film capacitor didn't look like it was in too good of shape either, so I replaced both of them with capacitors taken out of my spare ATX power supplies. I had an exact replacement for the 0.01 uF capacitor, but my closest match to the 0.22 uF capacitor was actually 0.47 uF (rated for the same AC voltage though), but I figured as an AC filter capacitor anything 0.22 uF or bigger would be fine as long as it fit on the board (and this did, with the lead spacing matching the hole spacing exactly).
 
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