WG6100 can't adjust B+

RetroHacker

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Well, I'm working on resurrecting a 6100 in my Star Wars. It actually does work, but the screen size is inconsistent, blooming on bright stuff more than I think it should. I just recapped the HV board, with slight stability improvements (screen doesn't blank out randomly any more). When I opened it up to install caps, I was surprised that the thing worked at all. The 33uf cap was bulging badly at the top, and a couple others showed signs of leakage.

Anyway, after replacing the electrolytics, I went to adjust the B+, and I found that I can't. It's reading 244 volts, and adjusting the HV adjust knob on the HV board doesn't change it. It also doesn't change the picture any.

So far, I haven't done anything to the deflection board, but I'm going to start investigating the HV cage more closely.

Any pointers?

-Ian
 
Did you replace the HV pot when you replaced the caps? Or replace ZD902 (not to be confused with Z902).

There is also a resistor on the deflection board that can cause this problem if it goes open, but I don't have the info in front of me right now. It is near the 800's, and has a marking of B+ near it...
 
No. Did not replace any components beyond capacitors.

I've got the HV board in front of me on the bench now, I've checked all the diodes, the frame mounted transistors, and several of the resistors, so far no problems. I'll pull the deflection board and start checking resistors on that too, so far I've done nothing to the deflection board - haven't even removed it from the monitor...

-Ian
 
Looking at the deflection board now, nothing looks burnt, and so far every resistor I've checked has been good. R612 is right next to a marking that says B+, it's marked as 3.3ohm, and it measures at 4.0 ohm. Within tolerance when you consider the nominal resistance of the meter leads is about .3 ohms.

-Ian
 
Yeah, well... I know I can *order* the right part. It's a matter of "what do I have here in the shop". I went through most of the different kinds of NPN transistors I have on hand, but most of them don't handle high enough voltage (40v versus 80 of the A06). But, I do have some MPSA42's... NPN and rated for 300v. I wonder if that will work.

-Ian
 
Well, that fixed it. The MPSA42 works as a substitute here. I was able to adjust the B+ to a sensible 180v. Unfortunately, now the picture is slightly out of focus, and I can't get it to uniformly focus with the focus control. It was never great before, becoming fuzzy on bright text. Now it's slightly worse, but at least now I don't have to worry about the B+ running at 240v.

Time to replace some caps on the deflection board and reflow headers...

-Ian
 
Well, that fixed it. The MPSA42 works as a substitute here. I was able to adjust the B+ to a sensible 180v. Unfortunately, now the picture is slightly out of focus, and I can't get it to uniformly focus with the focus control. It was never great before, becoming fuzzy on bright text. Now it's slightly worse, but at least now I don't have to worry about the B+ running at 240v.

Time to replace some caps on the deflection board and reflow headers...

-Ian

trust me and everyone else here, its best to replace everything with the deluxe kit from bob roberts, i did and it fixed all my problems
 
2n3904 or 2n2222 from radio shack :)

Nothing special about that regulator circuit that needs any special transistor... just make sure you get E/B/C right...

Yeah, from looking at the circuit, I didn't *think* I'd need anything special, but the thing that bothered me was the voltage ratings. Looking at the specs on a 2N3904 shows that they're only rated for like 40 volts, whereas the MPSA06's are rated for 80. According to the voltages in the manual, 40 volts should do it. But I assume those voltages are only when the circuit is working the way it's supposed to. I don't know if they'd swing high enough to blow a 2N3904 if the HV is misadjusted. I ended up using an MPSA42 because I had a bunch of them around, and they're rated for 300v. Overkill, but, whatever, it's like a ten cent part. Worked perfectly.

-Ian
 
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