Motorola roundie

[Electronic M]

Originally Posted by timmy

So when doing resistance checking at the tube sockets am I correct in saying check with tubes in place ?

Theoretically (unless you are checking the heater circuit, or the tube internally connects 2 pins and the set uses that to open a circuit if the tube is missing) it doesn't matter since there shouldn't be any flow between plate, grid(s), cathode, and heater when the set is off...The tube should act like an open circuit.

[jr_tech]

It is my understanding that Sams technicians made these measurements with the tubes in the sockets.

jr

[Yamamaya42]

Originally Posted by Penthode

I am very weary of stuck slugs. It is heat over time which makes it stick tight.

I have closeto 100% success by using a heat gun with a nozzle I constructed to focus the warm air towards the slug. Careful application of heat melts the wax and frees up the slug without risk of splitting it.

I have even had success with heat removing split slugs.

I would like to know the method for removing broken cores, cause so far, I have only ever had 2 that had broken/ split cores on my sets, but I have been lucky enough to find NOS replacements for under $10 each time.

This won't always be the case.

[timmy]

I there a metal Allen that will fit the slug snugly because plastic will melt after heating the slug because I tried the solder gun and it got hot but the plastic stick did not do the trick is there a specific known size Allen for the slug.

[timmy]

Ok well I took a shot and changed the 3.58 xtal and I now have really good color lock only now it looks as if I’m missing a color unless after changing the xtal I have to readjust the colors.

[Yamamaya42]

Out of phase, off frequency. The fact that a critical part was now changed, makes it all the more important that the Color AFC setup alignment be done to get correct colors, you can't just drop in a new type crystal and have it good to go, it will have different electrical characteristics, thus the even more need for the alignment.

[timmy]

Originally Posted by Yamamaya42

Out of phase, off frequency. The fact that a critical part was now changed, makes it all the more important that the Color AFC setup alignment be done to get correct colors, you can't just drop in a new type crystal and have it good to go, it will have different electrical characteristics, thus the even more need for the alignment.

Well I guess at this point the crystal was bad because I have color lock. This wouldn’t be the oscillator I would think because I have color and lock. The xtal I put in had the same numbers 357.545 I believe it was the same numbers as the old one.

[Yamamaya42]

You can't make that assumption by looking at the the video on your screen (color/lack there of), the only way to know it was bad, was to use an oscilloscope or frequency counter at the output of L35 at approximately 9.5v PtP at the correct frequency, all else would be assumption and speculation, by changing the crystal, it changed the whole dynamic of the color circuit, crystals also have load capacitance and drive level, in addition to frequency, thus should only be changed if you are 100% sure they are bad, cause unless you get an exact OEM, you always have to align after.

[old_tv_nut]

Are the voltages on the two paired caps more equal than before? This would indicate that the oscillator is closer to correct free-running frequency than before, but is not an indication that the old crystal was bad, just that this crystal is closer with the incorrect alignment settings. Unless you do the alignment, you are just waiting for trouble to occur again.

[timmy]

I guess there is no definitive way of knowing if the original xtal is bad because if the original is infact good then there is a component that has failed in the color circuit and if I find it I won’t have to mess with the oscillator slug at all in hopes finding what may be wrong and it will stay the way it was. The sams says to use a meter that they used back in the day I don’t have one just a digital meter.

[Yamamaya42]

https://www.amazon.com/Jiayouy-1Hz-5.../dp/B07P7GN8XF <-- i have this
https://www.youtube.com/watch?v=BiVnPr9-qIk
https://hackaday.com/2018/10/20/the-...esting-method/

[timmy]

I’m doing resistance checks on the color tube sockets the burst amp every pin is exact to the sams but pin 8 shows 5k but sams shows it should be zero this pin goes to ground. And I’m using the x2 output for negative pin 8 is heater how could it show anything.

[timmy]

V21-22-23 resistance checks are all on the money perfect but the other showing 5k is probably a typo on sams because it’s ground. Pin 8 v23 should be 680ohm but it’s 740ohm so that one has to go I missed that one all others are fine.

[Yamamaya42]

Originally Posted by timmy

I’m doing resistance checks on the color tube sockets the burst amp every pin is exact to the sams but pin 8 shows 5k but sams shows it should be zero this pin goes to ground. And I’m using the x2 output for negative pin 8 is heater how could it show anything.

V21pin 8 is the cathode of the burst gate, and is tied to ground, resistance check is in reference TO ground. ONLY pins 1,3,6,7 are tested from X2, all else, from ground.

[old_tv_nut]

Originally Posted by timmy

I guess there is no definitive way of knowing if the original xtal is bad because if the original is infact good then there is a component that has failed in the color circuit and if I find it I won’t have to mess with the oscillator slug at all in hopes finding what may be wrong and it will stay the way it was. The sams says to use a meter that they used back in the day I don’t have one just a digital meter.

To repeat: you cannot conclude that there is a bad component somewhere until you do the alignment. Then if you still have trouble, you can conclude there is a bad component somewhere.