Hoffman 610 Lost B+

[old_coot88]

Aha. So the center connection of R174A/ R174B, being left ungrounded, was breaking continuity-to-ground for the power xfmr's centertap, thus killing the B+ supply and the negative voltage supply.

[Doug66]

From what I can gather, Yes. The only info on this set is the Riders, which I downloaded from ETF. The schematic is very confusing. There are differences in it, and my set, and between the schematic and the pictorial of the parts diagram.

I don't know why Sams didn't cover this set other than a reprint of the original schematic.

I've ordered two 20W 1500ohm resistors to put in series with the center connection being grounded.

[Doug66]

Here is where I am today. Taking Bandersen's suggestion, I found I did have a 1620, 20W resistor on hand to replace the 10W that was frying for R178.

I've got 2 new 1500 ohm 20W resistors ordered to replace R174 candohm which I will put in series tying the center point to ground. For right now, I have put the old R174 back in with the center tap grounded.

That corrects my 260 B+ voltage. However, the 140 volt line is only reading about 54 volts. 260V should go into R178,and drop it down to 140, but it's pulling it down to 54.

I guess I will unhook everything tied to the 140V line and start checking

Voltages are now correct on V105 audio output 6K6 tube. Touching the meter probe to in 4, I can hear some static in the speaker.

[zeno]

I cant see the schematic, too small & blurry. Also it is
laid out messy. Give a point to Sams for drawing all
schematics the same & with sense.

If something is loading down a source & the dropping
resistor is the right watts it should get real hot fast.
Measure ohms to GND from the source. If it reads say
5K look for anything that is fed with about 5K resistor.
Example if a 4.7K feeds the G-3 of a tube there is usually
a decoupling cap to ground that may short. Pulling
any tube using the source is another test.
Another place I found a few times was the tuner B+
feed-through shorted.
Good luck

73 Zeno

[Doug66]

I'm back in business, sort of. Before I acquired this set, the member I got it from warned me ahead of time that a mouse had been inside the cabinet on top of the chassis. The mouse had peed all over the IF board leaving that part of the chassis rusty and corroded.

I had tried cleaning that part of the chassis with various rust cleaners and steel wool. Either the mouse pee had corroded some of the tube sockets or maybe a combo of the steel wool and cleaners shorted something.

With everything connected, I would get an arch in certain tube sockets, and several 1K resistors fried. After replacing 4 tube sockets, my voltages are back to normal. However, I've lost vertical as my raster has come back to just a line. I'll start troubleshooting the vertical now then continue loking into why no signal is coming thru.

[old_coot88]

Originally Posted by Doug66

...I had tried cleaning that part of the chassis with various rust cleaners steel wool. Either the mouse pee had corroded some of the tube sockets or maybe a combo of the steel wool and cleaners shorted something.

Steel wool? Yeeikes!!

With everything connected, I would get an arch in certain tube sockets, and several 1K resistors fried.

[Joe Connor]

Ah, yes, steel wool. I learned my lesson back in the late 1950s when I cleaned my Lionel train tracks with steel wool and some of the fibers remained behind. A very interesting light show for a 7-year-old.