hv issue
 

hello all, i have this set i recently got from a member here and no matter what i do to try to get the hv to go up it just wont.i have pulled the crt plug off, and the 6bk4 cap off,focus rectifer out nothing will raise the hv just stays the same.rectifier tube is good and tried a new 6bk4. any clues where to go from here, this is the motorola 23 inch color from 1966.:scratch2:

Low HV can be anything from oscillator issues to the flyback being bad. What's the drive waveform look like, and what is the HOT cathode current at?

well i didnt get to the cathode current yet as it is supposed to be 105ma but this hv is really low so i was thinking source voltages and again i didnt really dive into it yet but i will but just wanted to get some input from some of the pros here first.

Recapped?

ah,no not yet,lol.but it has a great picture with other issues as well.

On something that new I would avoid a total recap and would rather check each one on a eye type checker and replace only the bad ones so as to keep costs low, and avoid messing up the original factory adjustments by replacing caps that are still good. If a circuit is bad and all other parts etc are in speck then maybe a shot gun recap of that circuit is merrited.

Just my opinion.

Tom C.

well i guess but in this case its not only the hv but the width of the picture and height which i adjusted out but the controls are maxed out already and i know the hv has alot to do with those circuits so ill start in the horiz section and go from there. this hv is very low and there must be an obvious problem here, and this is an odd set it uses 2 horiz output tubes in paralle.

Hi, Timmy...

Have you actually metered the HV ultor voltage yet? If so, it might be helpful to post your findings.

When you say the Horizontal output uses two tubes in parallel, that means it's technically superior since you've got twice the net plate dissipation on the output. Anyone have a quick schematic of one of these type?

Also, when recapping, I kind of agree with what's been said here: basically I feel that the IF and tuner sections should only be messed with if something is way off. Just like a tube tuner's MPX circuitry. But the chroma boards in both SS and tubed sets could always use a tune up IME. And most importantly- the power supply voltages first initially(mains) and then the 1s derived by the flyback.

If you had to max out the height and width controls, you're missing voltage from somewhere. Start in the power supply.

yes i will be leaving the tuner alone for sure.and the hv at the crt is 12kv other bright scenes can go lower. the bright is turned down to keep it from blooming away to nothing, as well as the g1 control is down.and i do have a sams for this set.

Have you checked the B+? If it is low many problems can arise.

well im going to, i do think it may be a source but the way this set is made up i have to find either a tap or another way to test the b+. the chassis has all plugs and everything else is left in the cabinet. ill have to find a way to power up the main transformer to check these voltages, or course not under load but it should show something.

Power supply caps are likely bad, I suggest you sub those out to see if things improve.

yes i am about to cut a few out and check......

ok im revising what i said early here which is to much so now for 450v 80uf i have 480v 100uf.