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.

I think so; I wouldn't go that far off spec.

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.

That set should have a metal cover on the bottom of the cabinet like a Zenith. Tip the cabinet on its side and remove the cover to trouble-shoot the B+ circuits. Set uses a voltage doubler, like the earlier RCA's and clones. B+ should be around 380-400 volts.

For sure replace those doubler caps and the first filter, that alone should fix a lot of the issues with this set.

i posted in the vintage tv part of this forum about the red button breaker if anyone ever had low b+ due to black dirty contacts inside the breaker. odd as it may seem i got very little across the 2 terminals, continuity, and unless i played with the button pushing in and out and snapping it i then got good continuity.i took it out and cleaned the contacts as they were black and had no shine to them at all and its fine now. i know these breakers are problems but could there be high enough resistance between the contacts to give low b+ voltage. has this ever been heard of.

Sure it's very possible. I've seen many, many protection relays in stereo amplifiers which get tarnished contacts and lose either 1 or both channels.

Also, I had to jumper across the push-in circuit breaker while troubleshooting the 19" XAM color set...it would lose width and have sound crackle due to bad contacts in the breaker. Simply omitted it from circuit(abandoned in place) and added a line fuse.

well just waiting for 3 more caps and with the breaker now cleaned maybe this will do it.hopefully it will also take care of the hv issue being very low.

well just waiting for 3 more caps and with the breaker now cleaned maybe this will do it.hopefully it will also take care of the hv issue being very low.

If you had that much of a voltage drop in that circuit breaker, you'd know it. It's probably a 2 amp breaker. The breaker would get hot and arc. If the doubler caps are bad, it isn't even carrying the full current. First, you have to determine, that you have enough B+.

well the main source coming directly off the b+ diodes are supposed to be 390v so when im done with the caps ill see if that voltage is present. and yes your right the breaker if it did get hot its bimetal tab inside would have tripped it off and that has not happened.