Motorola 9T1 Restoration

[Jon F]

Thanks Tom I'll give it a shot.

[Jon F]

I put all of the original tubes back in just to be sure but the wavy-ness is still there unfortunately.

[old_coot88]

That bend is from a power supply filter cap. Any chance one of the replacements could be miswired or too-low a value?
(An example of miswiring might be grounding a cap that should't be grounded.)

[Tubejunke]

Originally Posted by walterbeers

Also if your putting your light bulb in series with the AC line, the bulb will light bright as the tubes will be pulling current to light the filaments. It's best to put the bulb in series with the B+ line, right before the rectifiers (diodes) which replaced the selenium's.

I never really considered the difference in using the 100 Watt lamp for "slow starting" a transformer-less set. The whole idea of using (normally) a 100 Watt lamp is to reduce the voltage/current available to and thus protecting a possibly expensive power transformer. This is a cheap, but effective way (for those without a variable AC source) of keeping from doing a lot of damage by introducing full line voltage to a device possibly dormant for decades. I used to do it a lot until I was lucky enough to find an old Select-a-Volt unit which is NOT an isolation transformer like a Variac, so it's not quite a safe, but just as effective. I now have an industrial size Variac, but it has some goofy plugs for input and output that I have no idea where to find, so for now I am not using the two ton monster.

[Electronic M]

Not all variacs have isolation...Mine for example is just a variable tap auto-transformer which has continuity between each respective input conductor and output conductor.

[Jon F]

Update, I've discovered why this set had brightness issues, the 8BP4 has a G1 short in it.

I came to this conclusion after I tested a 7JP4 in the set, and the 7JP4 did allow the brightness to be turned all the way down, and there were no retrace lines. The focus was also improved.

So I tried the "remove G1 shorts" function on my Sencore CR70. It actually worked, for a few minutes. The picture was much better and I could adjust away the retrace lines and have good focus and contrast. But, after 3-5 minutes the brightness would jump back up in a couple quick steps and be back to the way it was.

I also noticed no spark during the remove short process on the CR70.

Is there anything else I can do? I tried the "extended" G1 short removal process in the Sencore manual but that actually did nothing. I also tried rotating and shaking the set around and tapping the neck of the CRT with no change...

[bandersen]

So you were able to get your CR-70 working properly ? Does it still show a G1 short ? Given the scarcity of 8BP4s, I'd avoid being too aggressive with it.

[Jon F]

After running the calibration tests for the CR70, I determined the "beam builder" functions all work OK, the test functions are out on my unit. Since the 7JP4 worked good, it had to be the CRT and the symptoms were exactly that of a G1 short.

You're right, I think it's not worth zapping further. I left the tv running for about 20 min, and while the G1 short is not completely gone, the performance of the 8BP4 is better than before. If I adjust it just right, now I get a pretty darn good enough picture.

[Jon F]

Picture of it running today-