I found a newer model RCA 27" set (Model F27242GY, Chassis CTC185AB4) that does nothing when you hit the power button. I opened it up and found a blown fuse next to the AC line cord. What sort of stuff do I want to be checking on this set? I assume just throwing another fuse in and seeing if it works probably isn't the best idea...

Check the four rectifier diodes in the power supply. If those are good, check the regulator transistor in the power supply. If it's shorted, there are probably other components that the transistor took out. Last, check the horizontal output transistor. If the HOT shorts, it can blow up parts in the power supply. If the HOT is shorted, there's a good chance that the flyback transformer is bad. CTC185's had a lot of flyback failures.

I assume just throwing another fuse in and seeing if it works probably isn't the best idea...


You're right -- that is not the best idea on earth; in fact, it can do incredible damage, as I am about to explain. A basic rule of electronic servicing is to allow yourself one, and only one, new fuse when troubleshooting anything. If the new fuse goes, it is time to start looking for shorted or defective components. Something is wrong, somewhere, otherwise the fuse wouldn't have blown. Sometimes, actually rarely, fuses will "blow" for no apparent reason, simply because they are old.

However, in your case, I'd start looking for shorted transistors and the like if the second fuse blows. As I said above, if a fuse blows in a TV or anything else, you can just about bet that there is something shorted, a resistor gone way up in value upsetting bias voltages, etc. Normally, when a fuse blows, there is almost always an overload somewhere that must be tracked down and remedied before the device can be safely used again.

Do not, under any circumstances, jump the fuse or put in a larger fuse than the one that was in the set. Both dodges may get the set working, but it is a disaster waiting to happen if a short or an overload should occur anywhere in the TV. Non-technical people used to do this years ago with tube-type televisions, with disastrous results; in today's sophisticated sets with scan-derived power supplies and other complicated circuitry, jumping a fuse or replacing it with an overrated one can cause incredible damage -- not to mention starting a fire.

Found a shorted large diode right next to the FBT, couldn't make out the part index for all the dust and cramped space but it looks like CR4105 from the placement chart on the Sams photofact I found, the one right next to the FBT. Diode reads 0.000 on an HP 3466A multimeter on diode check regardless of the polarity. The 4 power supply rectifier diodes (4x 1N4002 near where the power cable goes in) seemed to read .5 regardless of polarity but I'm guessing that has something to do with it being a full-wave rectifier (there's always some combination that will open up diodes).

Where do I go from here? I didn't check those transistors, couldn't figure out which ones they were, and I'm not really sure how to check a transistor anyhow. I'm guessing if this diode attached to the FBT blew it's probably the flyback's fault, how does one test a flyback transformer?

Also, Jeff: Thanks for the useful safety advice. I do have an engineering degree, but my specialty was digital logic design, not analog electronics. I just assumed that if a fuse blew in a piece of equipment, something is probably wrong.

To test the flyback, you'll need a piece of equipment called a "ringer". Otherwise, you'll have to take a chance on replacing parts. It's very possible that the diode shorted on it's own. The horizontal output transistor is the big black transistor that's mounted to a heatsink near the flyback transformer. For best results, you should remove it from the circuit to test it.

In my experience, fuses that "just blow" due to age exhibit a tiny break in the internal wire, often at one end cap, which can be hard to detect visually.

If a large segment of the wire is melted/sagging, the fuse blew because of an overload.

If the inside of the glass tube is blackened or coated with vaporized metal, you have a serious short circuit to deal with. Don't even think of just swapping the fuse without testing the downstream components for shorts.

Check the four rectifier diodes in the power supply. If those are good, check the regulator transistor in the power supply. If it's shorted, there are probably other components that the transistor took out. Last, check the horizontal output transistor. If the HOT shorts, it can blow up parts in the power supply. If the HOT is shorted, there's a good chance that the flyback transformer is bad. CTC185's had a lot of flyback failures.


Your comment regarding flyback transformer failures in the CTC185xx chassis got me to thinking. I retired my RCA CTC185A7 and bought a flat-panel about four months ago. The CTC185 was still working like new when I put it into storage, 12 years after I purchased it. No problems whatsoever with the flyback, or anything else for that matter, except the antenna connector on the tuner PC board snapped off, twice, within one year after I bought the TV. But that was absolutely the only problem I ever had with it, unless you count a problem a service technician apparently found with the jungle IC. I never knew there even was a problem with the chip, as the picture on my set was always as sharp and clear as a good photograph. The technician told me that I probably would not notice the problem anyway, since I have cable; the only time I'd probably see it would be if I were using the set with an antenna, which wouldn't work in this area because I am too far from the seven Cleveland TV transmitters (just under 40 miles).


What was it about the CTC185xx series' flybacks that caused them to fail so often -- cheap construction, insulation failures after X number of months or years, breakdowns of parts ahead of the flyback overloading the windings, or just a run of bad flybacks? Were the last RCA CRT sets (CTC203, IIRC) this troublesome as well? I know RCA solved the onboard tuner problem starting with the CTC203 series, but did these sets also have as many if not more flyback problems than even the CTC185xx, et al.?

Beginning with the CTC185, flyback quality started going downhill. The 19"/20" CTC185 sets didn't seem to be as failure prone as the 25"/27" sets. I think they used basically the same flyback in the larger screen sets and it couldn't hold up to the extra load. The CTC197, 203, and ATC113 sets were very prone to flyback failure, especially the larger sets above 27". Then, there was the M134C, ITC008, and ATC010 chassis sets. These were cheap Chinese sets and the ATC010 had a built-in DTV tuner. I've seen many of these with a bad flyback that were only a year old. These last RCA's were so junky that I won't even take one in anymore.

Funny you mention the M134C chassis. I replaced a flyback in one the other day because the old one was arcing allover the body of the transformer. I tried cleaning the outside of it, but it wouldn't clean. It works fine, for a crummy design TV now, after the replacement. It lives in a bar, and theres lots of smoke, so I figured that the smoke had something to do with this failure.

32" TV. I've rarely seen a heavier TV, other than a big Trinitron!

EDIT: The bar fixed this set rather than replace it because the 4 flat screen sets they have have already died, while this one ran and ran. Again, the smoke coats everything. When I work on stuff for these guys, I do it in the garage. The smell is very strong in no time flat!!

I'm glad I never started smoking!

If there is a short in the high voltage it will kill the regulator transistor. This set uses a buck boost regulator circuit (I hope I remember that right). It is imperative you use isolation when working on that chassis as it is not the run of the mill RCA with a switch mode supply.
Also, the regulator must be well mounted on its heat sink or it will fail rapidly. There are some zener diodes in the power supply that short when the regulator dies.
Some service hints were jumper q4114 source to drain. Use a variac to adjust B+ to 95 volts. If the set turns on, adjust the variac so B+ is 125 volts. If all is well (except ripple in the picture) the power supply is at fault and needs service. Other notes I have are C4153 causes B+ to be about 80 volts and R4116 burns up. Q4116 if shorted causes B+ to be 60 volts with regulator working. C4106 fails, burns out Q4114. Replace with a .47 polyester.
Above all, again, USE ISOLATION TRANSFORMER!
I've repaired a good number of these sets and see mostly the 19 and 25 inch. I like them as they are good performers. They just have their quirks......

my advise from selling and working on rca tv set,s for over 25 years. leave that ctc185 alone run run away. sorry for my bad outlook but that,s just how the ball bounces on this set. steve

Beginning with the CTC185, flyback quality started going downhill. The 19"/20" CTC185 sets didn't seem to be as failure prone as the 25"/27" sets. I think they used basically the same flyback in the larger screen sets and it couldn't hold up to the extra load. The CTC197, 203, and ATC113 sets were very prone to flyback failure, especially the larger sets above 27". Then, there was the M134C, ITC008, and ATC010 chassis sets. These were cheap Chinese sets and the ATC010 had a built-in DTV tuner. I've seen many of these with a bad flyback that were only a year old. These last RCA's were so junky that I won't even take one in anymore.

These last RCA's were so junky that I won't even take one in anymore. you are 100% correct. the itc222 projection sets have made us some good money. steve

Probably the one thing that will determine if that set is repairable is availability of parts. I have found that aftermarket or generic parts do not work well in that chassis. If I remember correctly, there are some regulators no longer available. Generic flybacks rarely work satisfactory in that set either.
And yes, the sets after the CTC203 are complete junk!