RCA (Thomson) F20TF10 in a coma

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

I have no idea what you mean. Do you mean the screen control on the flyback? I see nothing labeled TDKS anywhere.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

yes on the flyback. we call TDKS

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

LOL! Ok, thanks buddy. That threw me for a looper. What's it stand for?

Turning up screen control on the flyback gives me a lighted screen with zigzag backtrace lines. Button presses on front panel have no effect. I'm guessing the crt is basically operational.

[Clydeuk]

Re: RCA (Thomson) F20TF10 in a coma

yes the crt, line and field sections seem to be working, as is definitely the heater. I can't believe it's been that long since I worked on a real CRT tv that I can no longer suggest the next step, I am convinced I have early stage dementia.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Me too on the dementia. In my vast technical experience I only worked in a TV shop for about 6 months back in mid 70s so I didn't have much to forget to begin with.

Anyway, it puzzles me why the HV, degauss and audio pwr amp are firing up when ac is plugged in. The heater I can understand for the "instant on" thing but as I recall the rest don't get power until the set is turned on. I guess I'll see about pulling the main board out and getting some pics. There are two other modules, one in a shielded box (but not the RF input box, that's on the main board) and another labeled EW Correction BD that has a coil and 3 trim-pots labeled EW-Amplitude, Trapez, and H-Amplitude.

[Andrew F. Ali]

Re: RCA (Thomson) F20TF10 in a coma

OK so you have HV, Heater filaments are lighting up but you have no Raster and X-Ray protect cct not shutting down the set in addition audio is OK, too. From the FB Trans you would be producing ABL voltage 200Vdc that go to the CRT and also the ABL cct.
There are two resistors that are in parallel typically 180K-ohm and 560K-ohm that send about 5.2V via a Zener Diodeto the ABL cct. If these resitors go open then you would get no screen light up (Raster)

OK so turning the SCREEN control on the FB Trans show weak raster and retrace lines. Look for those two Hi K resistors I mentioned. Your ABL/ACL circuit may not be getting voltage. Don't forget to return the SCREEN control to its original position. BTW if yo connect your antenna are you getting a dim/weak picture with the SCREEN control adjusted just enough to give alittle bit of light on the TV screen?? NOTE: Don't turn the SCREEN control all the way up it could trigger the X-ray/ Shutdpwn Protect circuit to go on.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

With screen turned up the RF input gives no response, none of the video or audio inputs do anything either. I haven't been able locate the two resistors and zener yet.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

1-how many volts on pin 5 BU004 crt board. 2- how many volts to pin 2,3,4,6 BU003 crt board.

[Clydeuk]

Re: RCA (Thomson) F20TF10 in a coma

I'm sensing if the set comes straight on and doesn't respond to standby commands maybe you have a problem with one of the power supply rails, or a faulty microcontroller/eeprom or something like that. I could be totally off here, some CRT sets used a momentary contact in the power switch to switch out of standby as soon as the power button was pressed in. Later sets had a more staged start up controlled by the microprocessor, or sometimes a dedicated micro for the PSU only. Degauss is usually the first thing you get when you push the switch on, I wouldn't expect the audio section to come to life straight away. The instant on heater thing was a relic, I'm not aware of any latter day CRT sets here that still used that, modern CRT heaters were pretty quick to warm up from a cold start, in later sets the CRT would remain cut off until the auto grey scale circuitry had done it's thing.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

1-how many volts on pin 5 BU004 crt board. 2- how many volts to pin 2,3,4,6 BU003 crt board.

1. BU004: pin 5 = 187vdc

2. BU003: pins 2,3,4 = 1.3vdc, pin 6 = 8.7vdc

Clydeuk, there is a <1/2 second delay between degauss and the crt HV quiet "crackle" and quiet bump in speakers.

Thank you guys

[kc8adu]

Re: RCA (Thomson) F20TF10 in a coma

you have a processor/power supply issue.
micro not running/held in reset due to it being bad or missing its supply.
since it commands mode,input,ect you wont get anything else.it also may switch certain power supplies too.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Ok please even need measuring 1.- emitter-TU81. 2 -pin 11, 8, 6 CRT. Hand reaches for the soldering iron to solder a collector TU61 and resistor RU61- as soldering looks bad

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

TU81
8.1v emitter

CRT
179.1v pin11
177.3v pin8
180.3v pin6

Touched up solder you pointed out.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

you have a processor/power supply issue.
micro not running/held in reset due to it being bad or missing its supply.
since it commands mode,input,ect you wont get anything else.it also may switch certain power supplies too.

Yeah, it looks that way to me too. I'm looking at the votage charts for the PSU and gonna slide the board out and start checking them if I can find them. There's at least one voltage I know is out of tolerance, 9VE is 8.1v and chart says min is 8.5.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

TU81
8.1v emitter

CRT
179.1v pin11
177.3v pin8
180.3v pin6

Touched up solder you pointed out.

I screwed up, the TU81 emitter reads 1.8v not 8.1v

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Now you have to check the CRT and for this first reduce the "screen" stay to slightly glowing CRT. Set in front of a mirror, it would be seen what is happening on the screen. Alternately one connect very briefly pins 11, 8, 6 with the ground while looking in the mirror to the screen. If CPT is serviceable, for every short connecting pin to ground the screen CRT will glow red, green, blue. If some color is not - then the CPT defective.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

I will do that kasfamily and let you know the results. However at this time I have the main board out and disconnected and ran into a slow down.

I had a problem disconnecting one of the CRT board connectors which pushed the solder pads off the board and broke a couple of traces because the connector shell was standing about 2mm off the top of the board and pushed the pins through the board when I tried to disconnect it. I've repaired that and checked the traces for coninuity and shorts. If you want to see my crappy repair job I'll post a pic. Those kinds of trace repairs always look horrid, don't they?

I had to pull the main board out to get at the power supply section and in order to get the main board out I had to disconnect cables. While I've got it out I pulled the bigger PS caps and tested them. They are ok. The power supply test points are marked on the underside of the main board, another reason to have to remove it. Anyway, once I get it all connected back and able to do the tests I'll let you guys know the results.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

The markings on this board doesn't jive with the votage chart on pg16 in the PDF I'm attaching. It is for a TX809 TVD809 and what I have is marked TVD/TX809. Number above 2111659A

Summary, I've got no low below 8.8 volts. 5v, 6v and 6.5v points are dead. Again the power botton has no effect.

UB = 117.9v
UA = 12.2v
12VE (doesn't exist on board)
14VE = 13.2v (doesn't esist on chart)
9VE = 8.8v
9VS (doesn't exist on board)
9VS2 = 9.4v
8VS (doesn't exist on board)
+5VE (doesn't exist on board)
-5VE (doesn't exist on board)
5VS = 0v
4VE (doesn't exist on board)
6.5V = 0 (doesn't esist on chart)
6.5VE = 0 (doesn't esist on chart)
6V = 0 (doesn't esist on chart)

Attaching a pic of the solderside of the board.

Kasfamily, before I do as you said can you please explain to me how shorting those high voltage CRT pins turn on (or up?) each of the color guns. Also it safe to use just an insulated test lead straight to ground or should I have some resistance in series? Just want to be care with the HV stuff Thanks.

Thanks again everyone for the great help here!

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Measure the voltage on the IP301 and IP330, and testing their name. About the test CRT ... TV should be turned on, to connect the pin CRT to ground, you can use a wire from the dmm. Enough for a brief moment to touch one end wire to the ground and the other end to pin CPT and look in the mirror to the screen tv. I check the wire from the device without the use of resistance. Security is recommended to all measuring of the TV with one hand, and on the other hand, must be behind the back

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Things have gone from bad to worse now; no HV from flyback to CRT anode so no can do the CRT pin grounding tests.

IP301 is a 7806A regulator
IP330 I can't tell, it is covered with a metal clip to the heatsink that I can't budge

IP301 has .01, 0, .07
IP330 has 11.67, 0, .74

I'm starting to think this is destined to be canablized for parts and recycled.