RCA CTC167CN - white lines on screen - light background

Hi. Got a CTC167CN. Came in DOA. Replaced shorted HOT, main fuse and 15 watt
2.7 ohm resistor in p/s. Runs up fine, but has light background with what
looks like retrace lines. Turn screen and biases down but still goes light.

Checked voltages at color gun inputs, somewhere around 20-25 volts, way low.
Disconnected the 2.2k resistors to the guns for testing. No effect on
voltage. When I turn off, voltage jumps up to around 190 momentarily then
drops off as p/s winds down.

Checked the 3 gun transistors and osd driver transistor, all check good.
Voltages at lum buffer trans running a bit low, around 2.8 volts. Video out
of U1001 proc chip are about 2 volts riding a 6 volt or so dc baseline.

Checked 190 volts up to crt board, there are 4 15k 2 watt resistors that
feed the guns and osd trans. These are all good, and voltage doesn't drop on
the supply side hardly at all, maybe to 185 or so, while fed side drops to
the 20-25 volts, whether connected to crt or not.

Anyone seen this? Not sure what to make of it.

Thanks in advance,

Danny

 

[Jason D.]

Checked the 3 gun transistors and osd driver transistor, all check good.
Voltages at lum buffer trans running a bit low, around 2.8 volts. Video out
of U1001 proc chip are about 2 volts riding a 6 volt or so dc baseline.

Checked 190 volts up to crt board, there are 4 15k 2 watt resistors that
feed the guns and osd trans. These are all good, and voltage doesn't drop on
the supply side hardly at all, maybe to 185 or so, while fed side drops to
the 20-25 volts, whether connected to crt or not.

Anyone seen this? Not sure what to make of it.

You do have leak between ground and fed side. Find it, usually a cap
but rarely can be CRT socket.

Also check Q1906 is good (luma buffer).

Cheers,

Wizard

Thanks in advance,

Danny

 

[Asimov]

"<djnoble35209@charter.net>" bravely wrote to "All" (22 Nov 03 00:04:10)
--- on the heady topic of "RCA CTC167CN - white lines on screen - light
background"

<d> From: <djnoble35209@charter.net>

<d> Hi. Got a CTC167CN. Came in DOA. Replaced shorted HOT, main fuse and
<d> 15 watt 2.7 ohm resistor in p/s. Runs up fine, but has light background
<d> with what looks like retrace lines. Turn screen and biases down but
<d> still goes light.

IMO is key -- turning screen down has no effect rules out the video end.
It could be an internal crt short or simply an open screen control gnd.
Test (with a high Z probe) the screen voltage range as you vary the pot.

.... High voltage can give a dangerously uncomfortable discharge.

 

Hi. Was the luma buffer transistor. Checked good on checker, but must have
had leakage. Put in a new one and set works like new, good strong voltage at
guns.

Many thanks all,

Danny

 

[john]

Best change those 3 filter caps that are around the Flyback Transformer as
well.

kip


--
"Watch the return E-Mail addy its false"
<djnoble35209@charter.net> wrote in message
news:vs05g61v3edq22@corp.supernews.com...

Hi. Was the luma buffer transistor. Checked good on checker, but must have
had leakage. Put in a new one and set works like new, good strong voltage
at
guns.

Many thanks all,

Danny