RCA 621ts Restoration

[earlyfilm]

Originally Posted by vts1134

. . . . . . I had prevously thought that the vertical was running too slowly but you can see now that is not the case. The horizontal white bands do not roll with this signal, instead they are steady right where you see them.

VTS1134,

OldCoot is suspecting one problem, and he very well may be correct.

Let's stop and think about the problem.

I see the vertical section attempting to run at 120 cps and it is badly speed modulating the sweep resulting in dual white bands. In other words, the normal 60 cps sawtooth is being speed modulated by a two backwards steps at a frequency of 120 cps.

The wrong speed operation could be caused by either a 120 cycle hum being fed to it from the power supply or from some component in the vert osc/output circuit being badly off value. (A heater cathode short would introduce a single band. Only the 120 cps hum can create a double band and 120 usually is only found in a full wave power supply.)

1) I assume that you do not have a service scope. If you do, the first thing to check is the B+ and B- power supply sources for hum. Then check to see if the waveforms from the sync separator through the vertical output are correct.

2) Substitute the vertical tube. If you don't have a spare, switch the video output 6SN7 with the vertical output 6SN7 tube. If this changes your problem, then you probably have a bad vertical output tube.

3) Since you restuffed the electrolytics, you might check to confirm that no electrolytic can became accidentally grounded. None of the original electrolytic cans in either the power supply or the vertical section were grounded when RCA built the set.

4) Check every electrolytic in the vertical to make sure you have a close to correct value and it is wired in with the correct polarity. On the Riders on the ETF website, which I've copied in an attachment, the positive side of the electrolytic is always marked with the section marker (ie, the triangle, square or inverted cup). Especially, check C127B between the height control wiper and the 100K going to the wired end of the vertical hold. Another possible source is an incorrect electrolytic across the cathode resister of the vert output. Also check C131B at the vert output transformer.

5) If you had a real mess up in the front end of the power supply you would hear a rather annoying buzz from the speaker, as the field coil of same is used as the filter choke. (If you have a loud hum, then pull the audio output tube and if it continues, then there is a problem in the power supply.)

Hope something here helps.
James

[vts1134]

Thank you for your thorough and thoughtful insights. I can answer a couple of things right away.

Originally Posted by earlyfilm

1) I assume that you do not have a service scope. If you do, the first thing to check is the B+ and B- power supply sources for hum. Then check to see if the waveforms from the sync separator through the vertical output are correct.

I have inherited a scope but it is badly out of calibration, and the probe is questionable at best. After reading a few period TV servicing books from front to back two or three times, and with several more on the way I have strengthened my resolve to acquire a working scope and learn how to use it. Unfortunately this doesn't help me currently.
One thing to note about the vertical sync pulses: I performed the following test. I disable the vertical osc by shorting the the grid to cathode and injected vertical grid pulses directly at the grid of the vertical output from my B&K television analyst. My thoughts were to isolate the output from the oscillator to see if the problems came from the sync/osc stage, or elsewhere. I'm not sure if I would have totally isolated the problem as being sweep derived (as OC suggested with the variac test), but the two white bars remained.

Originally Posted by earlyfilm

2) Substitute the vertical tube. If you don't have a spare, switch the video output 6SN7 with the vertical output 6SN7 tube. If this changes your problem, then you probably have a bad vertical output tube.

I had previously swapped the 6SN7s around in the set and the problem was unchanged.

Originally Posted by earlyfilm

3) Since you restuffed the electrolytics, you might check to confirm that no electrolytic can became accidentally grounded. None of the original electrolytic cans in either the power supply or the vertical section were grounded when RCA built the set.

I'll check on this.

Originally Posted by earlyfilm

4) Check every electrolytic in the vertical to make sure you have a close to correct value and it is wired in with the correct polarity. On the Riders on the ETF website, which I've copied in an attachment, the positive side of the electrolytic is always marked with the section marker (ie, the triangle, square or inverted cup). Especially, check C127B between the height control wiper and the 100K going to the wired end of the vertical hold. Another possible source is an incorrect electrolytic across the cathode resister of the vert output. Also check C131B at the vert output transformer.

I'll recheck all of the lytics, but I can tell you with certainty that 127A and B is polarity and value correct (in so far as the markings on the cap itself). It was one of the cans that I uninstalled and checked twice. Also R145, the 100K resistor going to the wired end of the vertical hold, checks ok. I'll recheck the other two capacitors tomorrow just to be sure.

Originally Posted by earlyfilm

5) If you had a real mess up in the front end of the power supply you would hear a rather annoying buzz from the speaker, as the field coil of same is used as the filter choke. (If you have a loud hum, then pull the audio output tube and if it continues, then there is a problem in the power supply.)

There is no buzz or hum in the speaker. I get audio output on channel 2 through my television analyst and what sounds like FM on channel 1.

I'll report the other findings tomorrow. Also if I have time in the day tomorrow I'll have some pretty pictures of the cabinet to share as I put some decals on.