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Craftsman RC200 resto - Printable Version

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RE: Craftsman RC200 resto - MrFixr55 - 11-28-2020

Hi TV Man,

You are obviously an expert, but please be very careful with that CRT. Looks like a 70 Degree Tube somewhere between 19-21". I was working on an old DuMont as a kid. I had the safety glass faceplate out and the 21" 55 Degree CRT slipped out of the mount. I was standing at the side of the set when this happened. If I was at the front of the set, I would have had a 45- 50 year career as a disfigured blind person selling pencils. The basement was absolutely covered with shards of glass. I don't think I found a piece bigger than the gun. I thank God every day (really) that I was not blinded by the incident, and wear protective eyewear any time I handle a CRT (not too often nowadays) but after a 40 year career as a Clinical engineer for a major automated clinical laboratory instrument manufacturer, I had different exposure hazards).

A fellow Phorum Member posts the number of times he was electrocuted. Between the CRT accident, shocks, dropping cars on myself, falling with a chainsaw on full tilt, 41 years of marriage and parenthood, a career that required me to visit hospitals through NY City at all hours, 1.2 million miles driving a car around NYC and Long Island NY, COVID and prostate cancer, the fact that I am still alive is proof of the existence of a Loving and Benevolent God!

Be careful and God Bless,

MrFixr55

Best Regards,

MrFixr55

RE: Craftsman RC200 resto - TV MAN - 12-03-2020

I got the audio section recapped. I was doing some tests and saw the cathode resistor boiling wax, so I stuck my meter on the G1 and saw 18v on one tube and 30v on the other. Suppose to be 0v, so it was a bit high. This completes the recapatitation of this TV, unless I need to go after some mica caps or a paper cap hiding somewhere (like the yoke). So, now to the troubleshooting. I want to get the BK1077 running so I can hopefully isolate the problem(s). 

   

Thanks for the advices MrFixr. I think the tube is secure. If it did fall, it's carpeted and would likely just snap the neck, which I dont want either. Kinda getting hard to find good picture tubes anymore.

RE: Craftsman RC200 resto - TV MAN - 12-13-2020

Had a chance to mess some more with this TV and did make some advances, but not there yet. My B+ voltages were quite a bit higher than specified, so I moved the line voltage selector (at the top pf the last pic) over to Hi. Well, evidently this means B+ and not line, or something is backwards, so I moved to the Lo and that put my B+ about 10v over what is on the diagram, and probably is right on if I used my old 1000ohm meter. 

Well, I had no video off the tuner but good sound. So I started making some checks in the IF section, since I can get video from an injected signal at the detector. I found an open plate resistor on my 3rd video IF, no plate voltage. Ah-Ha! So I replaced that and got  my plate voltage back - still no picture. Just a blank raster. I started to flip the channels for no good reason and when I hit 10, I had snow on the screen! Well, if I can get snow, this means the IF stages are now working, at least in part. So I fired up my modulator and set it on ch 10 and was able to tune in a picture, but no sound! Ugh! Gotta love these split carrier sets! So, I either get sound with no picture or a picture with no sound, which has me at the tuner now. 

I cant use my tuner sub box because this IF uses 22mc and my tuner uses the modern 45mc. So, I am stuck waiting on a capacitor for my 1077 from AES that has been across my state at least 2x and may finally make it down to my mailbox this week. I can tune it to the correct frequency and make some tests. .

RE: Craftsman RC200 resto - TV MAN - 12-31-2020

Progress:

I got the 1077 running and made some tests (starting to really like this instrument!).

First, AGC. I think I tracked down the loss of video. I could inject a reduced RF signal and get video to come through, sound weak. My voltage at the grid of the RF amp tube in the tuner was -1.2, and the video IF was a -few tenths. I concluded that my AGC wasnt working right and the pic overloads when I bring the signal up. I set a bias voltage into that circuit and found I could get a decent picture when I had the voltage about -5.75 volts or around. So, that confirmed I had AGC trouble. After some tests I found an open winding on the flyback transformer. It must have been near the bottom side since I could get a signal off the top, but had little to nothing on the bottom. This is in reference to the schematic. This set is more like the RC201 in most of the sections, so in comparing, I tried pulling the AGC signal (keyed) off the top of the winding, and after some experimenting, found that a 33k resistor was about right to make things work. 

Next, I went after the sync. I found I could lock in the horizontal sync with a grid drive signal injected into the H osc, but not before it. That told me the H section was working, and the problem had to be between the sync separator H take off and osc. I found I lost the signal right before the osc grid. It was tracked to a 1600 ohm resistor to ground when it should have been a 4.7 meg. I tacked in a 3.3 meg and got my H sync lock back. I don't know if that resistor was bad or if I stuck the wrong resistor (likely) in there when I did the recap. I'll look at some pics and tell later. 

With that done, I began refining some details, but found some problems with the H sync wandering. I could always sync it back in with the hold control, but was not right. Cleaned the control which helped some, but decided that something was drifting, got the freeze spray out and tracked it to a weird stack of resistors on the H osc (2 resistors soldered in parallel). Measured 4k when it should have been 2.2k. I changed that and so far, seems the sync has stabilized. I checked the resistors out of the circuit and it was goofy, think it was a bad solder connection. They were "piggybacked".

I decided to neat up the IF where I replaced an open plate supply resistor (just tacked a 3.3k resistor in place to make it work) and found that resistor tested all over the place when removed, I mean from inf. to 100k. I noted it was different from the average resistors, so I checked the Sams, it was just a 1/2 (although it looked like a 2w) 5%. There were 2 more that looked like the same type so I tested them. They were both way off spec, so I changed them too. The other resistors checked fairly close, although there are some cathode resistors that are off too. May change those as well. I am a little reluctant to change much in the IF due to the chance I may have to align. 

   

Now, a really weird thing - in making some checks in the IF section, I found if I touched the Fluke probe to the 3rd IF plate that I get a lot better sound and even improved picture. I can get about the same effect by clipping a test lead on and connecting it to nothing. I also get improved sound when I touch the G1 of the 3rd IF stage (even better), or G1 of the 4th IF,  but it degrades the pic. I'm not sure what to think of that. I also replaced the IF tubes with NOS with some improvement. Remember, my sound takeoff is right off the tuner, before the IF strip, so I am a little stumped why touching the video IF would affect the sound. 

Anyway, I think I am finally winning, and while not quite there yet, hopefully down to working out details and fine tuning.

RE: Craftsman RC200 resto - morzh - 12-31-2020

Good progress, Tim.

And, judging by this report, your COVID situation is improving (for you, not the COVID).

PS. If you touch the HiV and survive, that might kill off the rest of it. Icon_lol
Kirk can consult you.