rca ctc169CL5 - idiot me

[tmwalsh]

My sisters TV had no speaker sound, a bad tuner and the thing was loath to turn on. Found out about the smps diodes and caps. Fixed that. Came on every time, and stayed on. Excellent picture using a VCR as the tuner. Sound available from the earphone connection, hooked to input of stereo.
Found the voltage from U3101 not enabling the audio amp U at pin 3. Trying to probe, I crossed two terminals, and it went into runaway and fried. Replaced with new audio, and lifted a resistor R901 to enable the audio amp. Got the THWACK in the speakers at power up, but worked other than that. Set on shelf to return to my sister, but our TV died, so put it into use. Worked for a few weeks, then would not turn on. I pulled the power connector to the audio board, and it came up. Replaced audio chip, and re-installed pulled resistor to pin 3. Found damaged trace between R908 and Q601, and jumpered using blue wire. Reinstalled chassis.
Now, sound came up, no THWACK, went off fine. No video. Have OSD, have sound. Channels change, onscreen displays jump a bit vertically switching from 90 to 91 to 92 to VHF, as they should. Select out audio and composite work as good input to another set. S-video does not work, nor do the composite video inputs.

I think I fried something on the comb board, as the chroma is a straight(about 9 volts) line on the scope coming from pin 8 heading to jungle U1001, the luma out on pin 7 looks good. I errantly used the chopper heatsink to ground the jumper wire when I discharged the CRT. Only later to read, in ENGLISH, " heatsink is not grounded ". Whoops.
Is there any possibility that is is not the COMB board? The raster is black, but HV and OSD are there. 238 Volts on the cathode drivers(HI?) with no picture. Other voltages I have checked seem good.
Anyone have a clue?

I will post on sci.electronics.repair at groups.google if it will let me.

thanks for reading of my mistakes...
tom

[Wizard]

Re: rca ctc169CL5 - idiot me

I'm famillar with this chassis.

1. You used CORRECT DIODE? It is odd stupid picky design that *required* specific diode of all what on earth what RCA ever designed around it this SMPS and chassis itself?!

2. SMPS have 4 caps that must be changed but 3 caps is more critical: 2.2uF 100V, and 15uF 100V, and 39uF 100V (this was design change from 47uF in our RCA bulletin nearly one decade and half ago.) 470uF is simply DC filtering cap, any value larger than this is fine, low ESR better. like 680uF, 1000uF, at 35V. Adjust standby voltage for around 143V, I shoot for 142.5 to allow for tolerance creep as caps ages.

3. Be CAREFUL of the traces on bottom, they are DELICATE for handling and soldering which doesn't take heat very well compared to other makes I have seen.

4. Lost video is your video adapter circuit board (about 2" by 3" long standing up that faces you or PIP if equipped. If your TV have PIP either big metal box with 3 harnesses plugs to it or a about 4" x 4" open frame with tin cover on bottom and heatsink on a big IC again 3 harness cables plugged to it on left side of your chassis mounted to the TV cabinet's bottom seperate from the audio amp/audio processor circuit board. That harness goes to this video adapter from PIP. That is what I seen before when video path is lost but OSD working because the OSD RGB signal is working directly from microcontroller to the deflection/video processor U1001. (toshiba IC TA1880?).

Edit: Either video adapter board (stand up board) or PIP board is losing the video signal or PIP harness aren't plugged in. I have parts for these.

On ANY CRT-based stuff:
Always discharge CRT to OWN bare ground wire that is drawn tight across CRT bell!

Cheers, Wizard

[tmwalsh]

Re: rca ctc169CL5 - idiot me

Good morning, Wiz,
The replacement diode seems to be working fine. Standby adjusted to 143.5, low at 13.5. Solid, stable and functional.
This box has no PIP. My older box has the HUGE metal box which had the 'trots', which I have cleaned up successfully, but this one is not so equipped.

The video adapter board is the one that has the 40 pin IC labeled M50572ASP inside the RF can, standing up just to the left of the HOT heat sink as viewed from the rear of the chassis, directly behind the tuner, and at a right angle to the audio board immediately to its left. That is the board that has chroma and luminance separated, out on pins 7 & 8 on the bottom of the chassis, 18 pins(wires) coming through, labeled JM4001 to JM4018 I think. My board is about 4.75" at its widest, by 5" at its tallest.
In the doc, it indicates that this board, and an off-board delay line, are where chroma and luminance are separated. It is called the digital or analog COMB board in all I have read.
Now that the map has been drawn, it seems that the video is not coming out, especially the chroma. I see luminance on the scope, but the chroma is a solid +voltage. I *think* the messed up chroma fed to the jungle is destroying the luminance to Q2906, therefor no video, no snow, nothing but OSD.
The deflection/video processor (jungle U1001 )is a Toshiba TA8680. Voltages for the bright/contrast/ etc measure at or near spec.
These measurements make me think the jungle is not a-bungle... but is functional.

Here is the question: Should I remove the video board to inspect the backside for obvious smoke escape spots, or just try to find a replacement board?
You indicated you have parts. Would you like to sell me a board? The board has numbers on it:
6W81035-20N
8Q73012-01N
Diodes in the range CR401,402,...411 , transistors Q421, 426 on the silkscreen side.

Thanks for your consideration,
tom

[tmwalsh]

Re: rca ctc169CL5 - idiot me

Out of ignorance, I had always discharged the CRT to the metal rim/base of the chassis. This CTC doesn't have a metal rim, as it sits in plastic. I have since [ in the past week, maybe ] learned it is good to discharge to the aquadag. No problem there.
I put together a GR2000 in 1978, and it is still working, so I am not quite an ignorant idiot with a hot soldering iron.

I was trying to find out if it is likely that the IC on the board is toast or if it would be individual components such as diodes or capacitors. If it was likely the IC, it would be the death knell for this set, as I can find nothing to replace it, and Mitsu doesn't acknowledge that it even manufactured it on their web site.
I guess if no one knows, I will remove the board for inspection, but didn't want to waste time if it was the IC.

tom

[Wizard]

Re: rca ctc169CL5 - idiot me

Update! The video adapter board is the big than standard adapter because of IC hidden behind tin box? I happen to have it. It's at my work, will take a picture of it next week.

Cheers, Wizard

[tmwalsh]

Re: rca ctc169CL5 - idiot me

Good morning to those who ponder. I just got some real probes for my scope and checked the COMB out further. What I had originally thought was straight line voltage were actually signal data, with actual profiles. Wondrous. I have chroma and luminance signals coming into the T or jungle as they should, so I don't think it is the COMB, for which I have no documentation. My previous scopes, a Heathkit and an ex-AF Dumont with a dozen or so tubes, never showed patterns that matched the Sams fact sheets. Maybe it was the loose nut behind the wheel...
I just read of Krankshafts 27" Panasonic set with no video, but having OSD and sound. I read it all, downloaded PDF files, and thunk a bit. The description sounds exactly like what this CTC is doing. I thought that it had gone into some sort of shutdown protection mode because the R/G/B cathode voltages were all 238 instead of 200, but could not find any in the circuit nor the jungle (Toshiba chip) description. I had read of a vertical problem of some sort (caps?) causing video shutdown, but found no details anywhere.
Now that I know the COMB is at least sending, this should be a somewhat simple fix, but then again I won't count my chickens.

tom

[Krankshaft]

Re: rca ctc169CL5 - idiot me

Why are RCA TVs such a pain in the ass to work on?

I fixed a 36" for a buddy of mine I hated every minute of it.

Anyhow to discharge the anode to the dag simply take a screwdriver and get a nice thick wire put two alligator clips on it clip one end on the screw driver and the other end to the aquadag braid (the will be the black ground wire coming from this to the neck board).

This is what I do works everytime. I use my HV probe to discharge because I don't like nasty pops.

Also after shorting take the alligator clip off the screwdriver and put it on the anode cap the CRT can regain quite a bit of voltage due to the HV stored deep in the glass. I only had to get "suprised" while reinstalling the cap once .

Oh yeah and when I'm measuring voltages with the chassis on I solder little wires to the IC leads especially when working with SMT devices. The tolerances between pins on certain devices are just too small between that and you having the board vertical and it shifting and whatnot it's a recipe for disaster.

I remember when the board slipped and killed a 130V regulator I was measuring shorted the input to the output POP .

[Wizard]

Re: rca ctc169CL5 - idiot me

All capacitors/CRTs and many stuff that could store charge is what you saw is asborption charge coming out after intial discharge.

Cheers, Wizard

[tmwalsh]

Re: rca ctc169CL5 - idiot me

Finally got time for further investigation. Sat down on the basement floor with book and scope in hand. I used a VCR to send a test pattern into the set, recorded from a local DTV station setting up their broadcast equipment. Saw the stair step signals coming in and found them going out, but also found that the signal went flat on three lines that interface to the Micro, brightness, contrast, and sharpness. The thing they have in common is the Beam Current Limiter. I think I found my 'shutdown' point.
The base of Q2703, Beam Currnet Limiter is at 9.7 volts, and per the schematic is supposed to be 4.7 volts.
In looking at the schematic I would have expected a signal to be there at Horizontal frequency, but see absolutely nothing. It comes from the FBT on pin 6, through a 27K resistor leading to 3 side legs with
1) a 13.3k resistor to 26v source,
2) a diode with cathode end toward 9v source, and
3)a 10mf electrolytic capacitor negative side towards a diode cathode side to ground, with a 9v source and 2400 ohm resistor to the anode of the diode,
continuing to the beam limit transistor.
There is 9.7 volts on either side of the first diode, CR2706, and it measures 15k in both directions in circuit.
I will remove it to test, but would really like to know how this thing works.
The way I think it works is that it pulls down the signals coming from the micro when the transistor turns on, but the transistor is staying turned on when it shouldn't be. I keep staring, trying to figure out what happens when a H hz pulse comes through a 27K, pushes against 25v through a 13.3k, goes through a diode against 9v, through the 10mf cap to a 9v biased anode to ground. My limited analysis says this is a an rc circuit that is happy when it has pulses, and biases the transistor when it is sad. The capacitor must charge up and leak down at a specific rate, tuned to the Horizontal Hz, so the diodes balance each other out somehow and limit the voltage at base of the transistor.
I am going to get a software 'emulator' that will let me see what is happening. I think maybe the cap or diode(s) are bad, or the trace from the flyback is broken. There *should* be horizontal on that trace, and the thing is shutting down as it should. More investigation. Oh, my eyes are so whacked out looking at this board.
tom

[Krankshaft]

Re: rca ctc169CL5 - idiot me

I finally fixed the Panasonic the Chroma / Micro IC was dead.

According to Wizard these ICs are very sensitive and an intentional short as was in your situation may have fried an IC.

The high voltage from the CRT makes matters even worse.

If you can post the schematic of the circuit in question.

Remember next time DISCHARGE TO THE CRT GROUND BRAID .

[Krankshaft]

Re: rca ctc169CL5 - idiot me

As for where to get ICs and parts for TVs.

https://www.encompassparts.com/

I only use them for specialty parts flybacks, EEPROMS, Chroma ICs, Microcontrollers, etc.

Common stuff like vertical ICs and HOTs are purchased through run of the mill suppliers. Like Newark, Digikey, Mouser, MCM, etc.

[Wizard]

Re: rca ctc169CL5 - idiot me

No RC circuit for horizontal circuit. It is to filter out noise and keep the "turn-off" corner sharp (this is where horizontal transistor live or die), it needs help to force stored energy OFF or on sharply.

I should get some pics of schematics. on CTC169, there is no outputs on RGB for the microcontroller. RGB outputs from microcontroller for the menu text and closed caption to the jungle IC, PIP signal goes through this as well on same RGB lines. The other input is strictly Y/C video signal for main video. (tuner, inputs).

I'll have to check the schematic as was quite a while I had to consult the schematic for CTC169. Luckily I have downloaded it because my boss accidently threw all the paper form for earlier CTC1xx thru CTC203 out now we don't have much use for these. Sigh.

Cheers, Wizard

[Wizard]

Re: rca ctc169CL5 - idiot me

RGB output from micro goes to the transistors array for the RGB outputs that is served by the jungle RGB outputs (mixing in) for the text stuff and other circuits to keep text in sync with the picture (alignment).

The PIP takes h and v pulses from the other circuits and Y/C video signal from certain inputs or tuner and processes it for PIP and inserts into the main Y/C via fast switch IC.

horizontal drive is from U1001 pin 23.
vertical drive is from pin 29 as sawtooth.

The regulator next to the power supply transformer will only be supplying appox 7V if turned on (run mode). Also there are 2 other regulators that is 12V and 9V that is turned off or on, also there is third transistor/regulator that turns off and on 5V run.
This is also there is another 5V and 9V strictly for standby power to the micro and U1001 to get TV started up then other voltages will come up from the flyback and syncs in the main power supply (there is a small sync transformer isolation T4101).

Important that you have switch from micro turning these 5V and 9V run voltages on to meet the conditions.

I was not sure if you mentioned you are getting horizontal freq and getting CRT heaters glowing?

Cheers, Wizard

[tmwalsh]

Re: rca ctc169CL5 - look! A squirrel.. over there!

No PIP on this one. Brightness, Contrast, and Sharpness signal fed into the jungle from the micro. They are tied to a beam limit transistor that pulls them down when the beam sense circuit kicks in, at least that is what I thought.

I scanned the circuit, and tried to up load, but it said 'invalid image' for both pages. Tried twice. Tried as a .TIF. Invalid type.

I have standby 143.5, 13.5, Horiz, vertical, screen voltage, OSD works, audio works, tuner works, 238V on R/G/B transistors on the neck circuit board. This thing should work.
I think something is eating the signal from pin 6 of the flyback. I have traced from that pin to through the resistor to the base of Q2703, the BEAM LIMIT transistor. Using an oscilliscope, I do not see any signal indicating that the horizontal is oscillating, but I know it is because I have OSD any time I press 'menu'.
I just realized that the same signal is fed to the base of Q4110, called the BEAM SENSE transistor, back in the power supply, which I think it is a feedback to adjust the run voltage.
Hmm, that stuff is very near the chopper heat sink. [that I ignorantly used to discharge the CRT]... Ya think there may be a coincidence??

I had ignored that leg because the voltage had been regulated so well. In standby, for sure, but I don't remember checking run. Guess what I am off to do...???
Even at my old age, I am still amazed at how I can get going down one path and ignore what may have been the obvious.
If I find something in the power supply, I will report back.

tom

[tmwalsh]

Re: rca ctc169CL5 - idiot me

CTC169CL5
Well, I finally think I have a clue. There is a transistor Q4110, the 'beam sense', that takes a Horizontal freq pulse and feeds it back to the regulator circuit. From my measurements it is open. In circuit, it was 37k e-c, 39.9k b-e and 19.2k b-c. Out of the circuit, e-c is over 2000k in both bias directions.
Can someone tell me the RCA# to order or cross to a sub?
thank you
tom

Or, am I barking up the wrong tree yet again?

p.s. the markings on the Xistor are:
33010
T417
EBC

[Wizard]

Re: rca ctc169CL5 - idiot me

Put dmm on diode mode and redo the measurements on this transistor. Curve tracer checker (easy to build one and works with your 2 channel scope would help with odd reading transistors that looks funny with regular measurements to confirm.

Cheers, Wizard

[tmwalsh]

Re: rca ctc169CL5 - idiot me

I put the transistor in the Elenco transistor tester after the above posting. Set to PNP mode. The OK light comes on for a second and then gets dim, but the PNP indicator stays lit solid.
My ignorance comes to the front... Unless the battery is dead [which would mean the led would go out?], why would the test led say 'ok' and then fade out? Supposedly the tester takes the output of the trans in test and feeds it back to 2 amplifying transistors, one of which is fed to the base of the tested trans.... causing the trans to oscillate. [paraphrasing from the manual] part of the oscillations are fed to another transistor acting as a power rectifier which is to switch on the OK led. Obviously it must not be oscillating for very long, but I don't understand why.

I thought that because the Horiz pulse was not there from the flyback, it was being leaked to ground through one of the trans near the point where I grounded the crt, and messing up the regulator ckt. Checked Q4110 as it is fed from the fbt, and it seemed messed up in ckt. Now I don't have a clue.
tom

[tmwalsh]

Re: rca ctc169CL5 - idiot me

An update on the continuing tale...
After testing with the trans tester, I figured that it was not shorted and not open, just a little more power needed than the 9v battery could supply to keep it oscillating.
So, I then proceeded to zap the fuse, the 15W resistor and who knows what else by touching the scope ground probe to hot ground. [ the common point where two of the raw B+ diode leads are tied together.] There was a very small pfft and a bit of spark when I touched it, and the set went dead. I thought I just zapped the fuse, but found the anti-inrush 1.8/2.2 ohm resistor blown open also.
What did I do? I don't understand what happened. I was going to probe the signal on pin 16 of the regulator to see if it was getting feedback from the flyback, and realized I had to use hot ground and then Phfft when I touched the probe shield ground. It is acting the same as descriptions where the cap and diode on the horizontal return are bad or open, i.e. no horizontal deflection. I have not checked the horizontal output transistor yet.
I replaced the fuse and temporarily subbed a 10W across the open resistor leads, and now have a vertical line when I turn on the set. Standby power readings were good and stable. When I figure out what else is blown, I will order a 15W, too. What are the likely candidates to be zapped when the fuse and resistor open up?

New problems ...
My 2nd ctc169 has a clunk or rattle sound as if the degauss relay is clicking on and off intermittently. I *think* the temperature variable resistor is cutting in and out. It is the only one with PIP, and I have owned it since new. Had a power supply problem 10 years ago, and the shop lied to me, and gave me a chassis that was not the same as the original. It did not have the 'expanded stereo' feature of the original chassis, but I didn't notice for years. Has worked pretty well, but is getting a little tired where the focus is off a bit in the corners. Corrected by adjustment pretty well, but the clunks scare me. They can come in clusters, and then stop. I planned on borrowing the resistor from another set to test my theory. I have heard you can re-solder them if you have a powerful enough iron.

The 3rd ctc169 had a bad 2.2uf, so I borrowed from the 1st, and got it working. It has a black and white picture with no color. 15v standby is at 13.5. Now, when I check the regulated run B+, using a DMM, it turns the set off. This was the give away set, but has the cleanest chassis I have seen, almost like new. It is a twin of the next set... Both were owned by the school district, and surplussed, I think.

The 4th ctc starts off with a very dark picture, just able to see the brightest of whites, such as dress shirts and cuffs. After some 5 minutes or so, it gets brighter. This was the $23 set from Goodwill that has a perfect picture when warmed up. If something is going, I'd like to replace it before it takes out more expensive components. You can adjust the screen control up, and it will display, but becomes too bright as the set warms up. I left my DMM across the screen pin on the CRT pcb, and the picture was darkish until I removed the probe???? Maybe my DMM is pulling too much current when measuring volts? It is a Tenma with capacitor and transistor checker and Hz measurement. Seems like a pretty good quality meter until now. I think I will put in a new battery, as I saw a battery symbol flash in the LCD screen now and then.
These are all Proscan 27" direct view. I want to talk the boss into letting me get an blue ESR tester, is that a good idea? Anyone have feedback on my menagerie. At least now the victims are on a real table, along with the scope, and I don't have to sit on the basement concrete...
tom

[Wizard]

Re: rca ctc169CL5 - idiot me

3rd CTC, bad CR4118 diode. replace it will fix B&W issue and fix low voltage. This diode is strange, must be exact replacement diode.

The one with bad 2.2uF, you must replace all 4 caps in the power supply. 15uF, 39uF, 470uF and this mentioned 2.2uF. Low ESR is required.

Absolutely get the ESR meter.

Cheers, Wizard

[Wizard]

Re: rca ctc169CL5 - idiot me

All this accidents is what I Have told you to run chassis on the isolation transmformer always when measuring with scope or meter for both safety and cut down accidents.

Remember, cold side, stay in there, or hot side only when measuring. Not across hot-cold.

Keep asking.

Cheers, Wizard