CTC169 36" dead

Hi...

Take a look at the 15v supply, if there's a fair bit of ac ripple there, go ahead and change c4145.

Take care.

Ken

i used an ESR meter. the cap has very good ESR, i shoudl change it though. but nothing makes since. the 13.3v is solid, even when you press power button, unlike before. i thought its supposed to raise when power pressed, it doesnt.

im going to scope it and be sure. good point. ;-)

i think something somewhere is funky. I scoped out the 15v standby, it looks like sawtooth, with a ringing on the up-ramps.

when i press power, you can here the supply "tick" and the sawtooth gets considerably larger, and then drops back down the way it does. the cycle repeats each time i hit power.

i scoped the 26v source from the power supply, it also has this "sawtooth" ripple, but its considerably smaller. although still preseant.

any ideas?

On Sat, 27 Jan 2007 12:37:43 -0500, Mike Has Frothed:

High ESR caps

i replaced the cap off of the 15V standby, and i still get the same shit. im at a standstill im assuming somethign is loading the standby down, shorted somewhere.

as the set only fired up once wiht HV. and never did it again.

the HOT tests fine.

i think its the horiz circuit.

When i press power, pin26 of U1001 jumps to about 8.6 volts. holds it for about 3 to 5 seconds, and drops back down. jumps back up each time i press power.

there is NO drive on the HOT. on any attempt. even on plugin. no drive. somethings up.

Weird.... the 26 volts you mentioned was present in a previous message is derived from horizontal scan... ???

Ken

no. from the chopper.

i have nothing from the horiz circuit. the horiz circuit has failed.

i think U1001 is bad.

i removed the horiz drive xistor. when power is pressed, NO waveform on the base of the transistor. im looking for a strong saw or square wave i assume. well i have nothing but a little bit of noise when the power is pressed. and i have to crank the scope up to see it.

now if i scope out pin 23, the H-drive out. i have the same type of noise, but a little bit bigger in amplitude.

shouldnt i have a strong defined square pulse? at 15.25khz. well i get a faint bit of noise. almost like a ring type of noise.

when power is pressed, the 9v VCC to the hoiz osc of U1001 goes present. so whats left. U1001?

Hi...

What's the voltage on pin 16 u4101? (power on, let it run for a few seconds while you watch - wandering around?)

Take care.

Ken

no. stays a solid 51.6vdc

i moved my ground probe to the negative side of the primary, i had it on the negative side of the secondary, this time i get a rock solid 10.2v

Right where it should be; indicates that the set "isn't turning on" as opposed to being held off by its own protection circuits.

My address is good; send me an email from an address that can take a few megs of attachment. And if necessary, do whatever you have to so that attachments from me are acceptable

Take care.

Ken

ok.

maybe a picture is worth a thousand words.

here is the scoped output of the 15v standby. also the same waveform is present on all the outpus of the power supply. the waveform gets a little bit larger when the power button is pressed.

Also, you see the ringing on the peaks? well when i scope the output of the U1001 to the driver transistor, i get a flat line, with the same exact ringing. but no square output. horiz VCC goes to 9v when power is pressed, and drops back to 0v approximately 3 to 4 seconds later.

im not sure what the issue is. looks liek something is seriosuly loading the supply. but im not sure. all 4 caps in the primary have been replaced, and the cap on the 15v CR4118 was replaced, along wiht CR4118.

im assuming the "ringing" is the power supply turning on to charge up the caps to get the voltage back to what it shoudl be, and the steady decline is the caps discharging, then hits the threshold, and supply starts again.

for the hell of it, i disconnected the amplifier board completely from the circuit, all plugs, and unsoldered the entire board.

the ramp pulse with ringing is still present on the power supply.

but now, when i scope U1001, when i press power, my pulse is showing up now. it wasnt before. wtf...

nevermind, i spoke too soon. its gone again :-(

im guessing either the ramp noise from the output of the supply is disturbing the IC, or U1001 is intermittantly defective. :-\

it was audio out board. i plugged the horiz driver xistor back in. its not dead anymore. although somtiems it turns on now. sometimes it doesnt. but if i plug the audio board back up. it wont work at all.