got this today, CRT test good and tracks well so that is a major plus.

the B+ boost cap (.1 1kv) was open, the only other paper was a .047 that was across the B+ which was leaky. Both of these were the paper in a ceramic tube type caps.

There was also a burnt resistor, a 33k that goes from the 145 B+ to the cathode of the audio out, then 180 ohms to ground. Its forming a voltage divider at the cathode (145+,33k,cathode,180,ground) but not sure why its done that way. Anyway its smoked and now its replaced.

I did find a cathode short on that tube, and the video out and one other compactron. these were hard shorts that did not respond to banging the tube and the short indicator was pretty bright.

Before doing any work I did have a weak pic and some audio but I did not test it long.

I will replace the tubes tomorrow morning and see if that replacement 33k resistor gets too hot.

I don't do the automatic replacement of the filter and doubler caps, I will try it out and see how it works, check the B+, check for heat, look for evidence of cap failure in the pic and sound. If all good I will just leave them be. Its a string series set so I am not too worried about a filter cap taking out a transformer.

There was also a burnt resistor, a 33k that goes from the 145 B+ to the cathode of the audio out, then 180 ohms to ground. Its forming a voltage divider at the cathode (145+,33k,cathode,180,ground) but not sure why its done that way. Anyway its smoked and now its replaced.



That was a trick to create a lower B+ voltage for the tuner and IF strip, and so as to not waste power when doing that voltage drop, that otherwise wasted power was put to use as the audio output stage. The audio output tube current was effectively put in series with the total current drawn by the tuner and IF tubes.

This is not a stacked B+, there is a separate 145v B+ already from the power supply.

Dan (ctc17) was thinking it maybe a hum cancelling circuit. Feed the ripple in from the audio out plate B+ to the cathode to modulate the bias. there is no cathode bypass cap in the circuit, just the 180 to ground, so you have negative feed back from the unbiased cathode resistor AND hum bucking from ripple off the power supply.

the real question is why did the 33k smoke, my guess is the short is a HK short and since the audio tube is near the begin of the string, maybe a short there somehow caused s surge, but I would have thought the 180 to ground would have suffered. I am not going to expend a lot of energy trying to figure that puzzle out, as long as it does not happen again (after replacing the shorted tube). I will be checking the pin resistance to make sure the 180 cathode to ground is ok.

hmmm the plot thickens, R314 which is the cathode resistor to ground on the audio out, read 15 ohms should be 180....

Pulled it out and double checked out of circuit, yep perfectly good looking resistor brn/grey/brn, reading 15 ohms.

would like to add that the 280v source uses a doubler circuit, where the 145v circuit (which in this case powers the audio with the smoked parts) uses a half wave off the mains, hence will prob have a fair amount of ripple.

I have been doing some seaching around I have found some support of hum cancelling circuits that do use PS ripple applied at the cathode to cancel out hum. The circuits are a bit different in how this is accomplished but thats the idea.

the real question is why did the 33k smoke, my guess is the short is a HK short and since the audio tube is near the begin of the string, maybe a short there somehow caused s surge, but I would have thought the 180 to ground would have suffered. I am not going to expend a lot of energy trying to figure that puzzle out, as long as it does not happen again (after replacing the shorted tube). I will be checking the pin resistance to make sure the 180 cathode to ground is ok.

It may not be germaine to this case, but occasionally a smoked resistor in the B+ chain is caused by a large ripple voltage due to an open filter cap directly 'upstream' from said resistor.

Blue balance pot (trimmer on the PCB, not the drive or screen pot) is bad.

This is a 2k pot. I will work on getting it out later, and then just tack in a couple 1k for a fixed voltage divider until I can find the correct replacement.

The problem shows up as no blue in the color programming regardless of screen or drive settings. My guess is the imbalance in the circuit is just cutting off the blue gun completely. If it rock the tuner off channel to get a blank raster I can adj the drives as expected for a grey screen, but as soon as I try a signal all I get is red and green, and even then the green is not quite "right" I presume due the the absence of the correct blue color difference amp cathode bias signal used to matrix out the green.

ok I cheated, just soldered in a 1k from the center tap to the open side, so I still have some adjustment. I don't really think its all the critical. I must say this set make a MUCH better pic than my other PC. there is no overshoot of colors and the tint control is much better. I will get pic soon.

set has a 11WP22 crt, I seem to recall reading (maybe hear by KX250, that it may have a finer dot pattern).

turned in on, no pic, HOT is starting to red plate. checked the grid drive, its there but a bit low at -26vdc. No glow on the neon bulb tester at the HOT but a little around the fly. I disconnect the HV rectifier tube and try again, this time I get neon at the HO and see arcing at the tube cap to the plate of the HV rectifier. Its an odd ball a 1DG3 with an odd octal filament base of 3 and 8 not the normal 2 and 7, my mercury tube tester can not test it. Rather than dragging out my hickok 533 and trying to figure out how to configure the switches, i just subbed it, a better test anyway (I happened to have a NOS handy). Bingo HV back. Bugs me that I can't test the tube in the mercury 1000.

why the heck did they have to use such an odd ball tube?

oh rechecked the HOT grid drive for future reference -36v

here are some pics