roundie color sync

[DaveWM]

argh...

all ready for Rockford and

my philco started acting up a couple days ago. lost color sync. turn it off and on and it would come back and be fine until I turned it off.

few days later and now I cant get sync lock no matter what. tried several 6gh8's (osc tube), no joy, and the turn off, turn on trick is not working.

I wonder if it could be the 3.58 mhz crystal?

I will try it again in the am and see...

[DaveWM]

still not working this morning, I think i will try another crystal next.

[oldtvman]

If you have a way to check the capacitors in the oscillator circuit that would be the best way, otherwise you might have to shotgun the circuit and replace them all.

Do you have an oscilliscope?

[DaveWM]

yes I have a scope, and a cap tester (eye tube type that can test at rated voltage up to 450v)

I guess I should 1st check to see if the osc circuit is indeed osc using the scope?

[DaveWM]

well, I got the sams out, will start with resistance checks, then voltage checks, then scope around the osc section.

[Don Lindsly]

Run through the Chroma AFC alignment per instructions. If it will not line up, or still drifts, replace the color oscillator and burst amp tubes.

[DaveWM]

ah ha...

checking voltages (resistance looked good) and the screen is at or below 100 should be 125, then I check the 275v source (which is dropped to get the screen voltage) and its at 257v.

I know osc tube can be finicky about low voltages (at least in FM radios and I presume in TV that have 6gh8 tubes) so I will need to check this out.

the voltage starts out at 290 but drops fast.

Tube grid should be -5 but its more like -.2

I guess there maybe too much of a load somewhere dragging down voltage on the 275v source.

[DaveWM]

I do have a variac, that will allow me to up the line voltage somewhat, I think I will give that a try as a quick fix.

[DaveWM]

no help with the variac. gonna pull the chassis and check the B+ current draw to see if excessive. I may just go ahead and swap that crystal while its out. The sams did not give any wave forms to check on the osc tube, just the chroma sync pulse that goes to it, so I can check that before pulling.

[ctc17]

First thing I would have changed was the crystal. NTE358, NOT those little ones they sell in two packs. They cant hang with the 80 volts or whatever the thing has accross it.

[DaveWM]

well dude, I shoulda done that 1st thing like you said

ta-da new crystal and bingo, back on track.

I had a few old ones I got from a surplus store, the big ones, perfect fit.

Soooo I will button it up tomorrow.


wheww, note to self, replace the (&*(&(& crystal next time

[ctc17]

Thats why my thing says barber poling rainbow. I have change a bunch of them. Usually it starts off bw then as it warms up you get the rainbow then it locks in.

[DaveWM]

I think next time I pull the chassis I will see if I can install a xtal socket to make it a LOT easier to replace.

[DaveWM]

got it all buttoned up, reset all the screen drives for grayscale, checked the HOT current (240ma vs 220 per the schematic). I did not bother to check another 6DK6 to see if that would drop it. I need to check the HV to see how that checks out.