RCA 46" TV P46725SK won't turn on

You are going to have to do basic tv troubleshooting and post the results for any help. There are not easy answers. So far we know the set does not turn on and needs repaired.

If you do not have the proper training and equipment, it is better to pay for a quality estimate on the set so you can make an intelligent decision on whether to have it repaired or not. Most RPTV repairs fall under $300 total in home in most US markets.

Whats the ctc number on it ??

Does ctc number = chassis number? If so, the chassis number is PTK169PFA.

I have some troubleshooting skills - I once fixed my Defender arcade game monitor (bad flyback transformer). I have no schematics or tech info other than a parts list and board ID sheet I found under the back panel of the set. I have a DVM. It's not clear how to discharge the flyback transformer... it's not like a regular TV where you'd slip a grounded screwdriver under the rubber cap. Here the HV lead disappears under the three projection tubes. Not sure how to get to those w/o zapping myself in the process.

What else to check?

kip wrote:

That's a CTC-169. It is a good chassis, a bit old now. Was the picture good, and did everything else work well before it developed the problem? The good news is...you don't have to remove the entire set. The internal light box, 70 pounds or so, is removeable, so a technician can simply come to your house and remove the chassis, take it to the shop, repair it, and return it. This chassis can be a bear to troubleshoot if you don't have the pertinent service information available, though.

Tom

I remember a few CTC 169's with the sound output IC shorted. That could cause it to go into the shutdown mode. Suggestion, remove the power for the audio IC and see if the TV will start.

Yes, it was working great, no sign of any problem, then yesterday it just didn't turn on. Come to think of it, we had a power outage the other day and I can't remember whether the last time we used the TV was before or after the outage. But we get power outages all the time in my area so I don't suspect that caused the problem.

First thing remove the light box (presswood box all chassis & CRTs Mounted. If there is acover on fromt of box (convergence controls ) remove it. the HV divider block is behind it. Locate thr red wire off slightly by its self (goes to HV transformer) remove it Put into a dry class bottle (for insulation purposes) Now hook up speakers & attempt to turn on If sound returns You have a bad divider block, or a shorted anode lead to one of CRTs If sound returns plug wire from transformer back in & remove the red wires going to CRTs one at a time & try turning on. This will isolate problem to individual tubes If this checks contact me & I'll make further recomendations snipped-for-privacy@corrcomm.net

How should I disconnect the main HV wire w/o zapping myself?

Just pull it out...It wont bite.

Okay - with the main HV lead disconnected from the HV divider block, the sound returns.

With the HV lead reconnected, and disconnecting each individual CRT wire in sequence, no sound again (except for the tick-tick-tick). Then I disconnected all three CRT leads (in case two anodes were bad) and still no sound.

So - replace the HV divider block?

And repair the main smps power supply which is the typical cause of the hv block failure. Do not forget the hv splitter rubber insulation boots that are on all the wires.

Would installing Tritronic's Common Failure Repair Kit (p/n CTC169-KIT-PTV) do the trick?

What is the problem in the power supply that causes the HV divider to fail? I have fixed many of these and while we routinely go through the PS I have not ben aware of the PS causing the divider to fail.

Leonard

High B+ regulation in standby. The margin for error is very small on the hv in the splitter. As the capacitors fail in the power supply, the standby voltage will drift over time up to as high as 165V, versus the 140~145V that is suppose to be there. Since that is a 15% increase in initial B+ at start up, which is beyond the 10% margin for the insulation in the hv block, the hv is too high initially at start up and this starts internal arcing at start up. Over time these carbon tracks finally cascade and the hard carbon arc short is started. The problem arises in that the regulator kicks into run mode in about one second after turn on. The regulator is then running off the horizontal feedback pulses for regulation. Since this happens so fast and is only slightly above the x-ray trip voltage, the x-ray circuit never triggers. Each turn on with standby B+ running high will cause an arc over. The big problem we found was that if the smps was not repaired and was the cause of the failure, it most times would take 6 to 9 months before we would get a call back on the set being dead. So shop policy had to be verify the smps secondary voltages on ALL ctc169 sets, cr4118 and cr4116 must be in proper range and clean looking on the o'scope. Extra 5 minutes of work to guarantee no future problems.

The cr4118 failure can also cause the B+ to run high as it starts to go leaky and fail. However I have never seen it fail to the point that the B+ will run over 150V before the 15V line was too low for the set to attempt to start up.

It is mainly the 2.2uF capacitor on the standby feedback line of the smps that goes open that causes this problem. It is a simple matter to measure the standby B+ voltage on the cathode of cr4116 with the tv turned off to verify that there is not a problem.

Interesting. I never noticed the standby B+ going that high. I'll have to check more closely. We have several routine checks on the 169 chassis on any set that comes in that includes the caps in the power supply so the get changed if they are bad. I often don't check the standby B+ until after the repair is done so I had not noticed that. We do, however, change lots of HV dividers in sets where the PS caps are fine. In those cases the B+ is checked and I have not seen it out of range. I guess the small margin of safety on the divider is the problem. I have also changed quite a few that were dne by other shops previously and the grommets were missing or the lead was not inserted correctly. So the OP should be careful to install it correctly or be prepared to change it again before long.

You wold think that they would not start the horizontal osc. until B+ is regulated. But then, you would think a critical part like a high voltage splitter would be built with a greater safety factor.

Thanks, David.

Leonard

Coincidence due to age? Maybe. What I find mostly is the cap will be marginal. After the set is plugged in a while it all warms up and the B+ seems to be close enough to the ideal 143V. But when the set is cold, the B+ is higher. Typical bad capacitor problem.

A 10% increase in B+ on start up is a 10% increase in HV, 28,000 volts is quite a lot less than 30,800 volts.

They do have the unit regulating at start up. The standby rough regulator feedback is doing the regulating, when it fails to regulate on the money, there is nothing that will keep the set from coming on, until it goes so high that there is a catastophic failure.

So as always, check/replace the capacitors in the smps and cr4118 everytime.