Quote:
Originally Posted by old_coot88
Zeno's right. Those 2 ground stakes on the far right end of the chroma board need to be re-flowed. They're Schroedinger's stakes and exist in one of two states: either cracked or gonna crack.  When that happens the 6GU7 heaters go out, initiating a cascade. Plate voltage rises, and since the plates are DC-coupled to the CRT grids, CRT beam current rises, dragging down the HV till raster blooms and fades out, stressing the bejeebers out of the 3A3 and flyback.
Re-flowing these should be done as a matter of course on every CTC-15, '16, '17 and '25. |
I did read in one of my books something about "a set shouldn't leave the shop without reflowing the solder at the ground joints on the chroma and IF boards"
I did reflow the joints and check them but only on the chroma board, and AFTER my focus went out. Having done that, the focus is still poor and the focus control has only a subtle effect on the picture. I'm not sure if what you described above is what happened or if my coil is bad or the 66M bleeder or something in that circuit has gone bad. 6GU7 filaments are present, currently.
I've read that focus voltage @ the CRT needs to be about 20% of CRT HV, so ~5KV. Need to test that.