Riddled TV Repair Forum

chumba · Joined: 01 Jul 2009 Posts: 66

Have a Toshiba model CF30F40R TV with tuner problems. Intermittently the picture gets white lightning bolt-like flashes on the screen with accompanying loud audio static.
Looks like this:

Link:
http://img193.imageshack.us/img193/292/200902200005.jpg
Component inputs work fine and coax connector looks mechanically solid. Problem follows on channel 3 or 4. TV will sometimes go 4 hours without this showing up and then all of a sudden starts acting up.
Have already tried resoldering the tuner pins & case/ground to the PCB and blew out the dust.

Google

chumba · Joined: 01 Jul 2009 Posts: 66

Does anyone know the test points on this tuner to check for tuner supply voltage and channel switching pulse? This tuner has an AGC adjust screw on it that I haven't touched yet.

Jesse Mack · Joined: 22 May 2008 Posts: 600 Location: The Last Frontier

I would strongly suggest that you remove the cable box first. Hook up your DVD or VCR using RF I/O from the VCR or DVD going directly to the TV, without the Cable box in the loop, and see if the problem still exists.

Since it does not do this using other inputs you must remove the source from the equation as being the problem.

Jesse

chumba · Joined: 01 Jul 2009 Posts: 66

I have tried connecting another satellite box using the RF connection and the problem still persists on the TV.

JTS1957 · Joined: 21 Jan 2009 Posts: 2395 Location: Far, Far Away

I think Jesse means you should try a totally unrelated source (DVR/VCR connected to the RF input of the TV). Unless you are SURE that those particular receivers work on another TV - in the SAME location using the SAME wiring.
For example: what if the LNA for the satellite receivers has a problem. Cool

Google

chumba · Joined: 01 Jul 2009 Posts: 66

The TV shows the same problem using a VCR source also. It looks like the tuner freq. lock may drift while the flashing & noise is occurring - it seems to be slightly mis-tuning to the high side of Chan. 3's freq.

chumba · Joined: 01 Jul 2009 Posts: 66

The following DC voltages were measured on this tuner, part # EL923L2:
Pin1: 2 mV
2: +32.4 V
3: 2.9 to 4.1 V
4: 3.4 to 4.2 V
5: not connected
6: 4.7 V
7: 5.1 V
8: 6.7 V
9: 8.6 V
10: 3.0 V
11: -0.2 mV
12: 2.1 V
13: all over the place
14: - 2.0 mV and goes to -1.4 mV when CHAN+ button pressed
15: 5.0 V

Does this point to anything? I believe the 32 V is the correct supply voltage and it is there. Anything else to check?

JTS1957 · Joined: 21 Jan 2009 Posts: 2395 Location: Far, Far Away

If you are POSITIVE it is the tuner that is causing the problem ... why mess around? $27.00
www.tiptoptuner.com/

To prove, I'd pull the tuner and input an I.F. signal from an Analyzer to the I.F. pin FOIL.

chumba · Joined: 01 Jul 2009 Posts: 66

Am not positive it is the tuner, that's what I'm trying to find out.
Don't have a signal generator...could I instead remove the TV's tuner and inject the RF output of a VCR?

JTS1957 · Joined: 21 Jan 2009 Posts: 2395 Location: Far, Far Away

NO you can't.
The IF output of the VCR's tuner - MAYBE. But then you'd have to make sure you isolate one of the units from the AC outlet so you don't blow fuses when grounds are shared.

R.F. = Radio Frequency I.F.= Intermediate Frequency