Resistor or jumper at hv rectifer socket: Zenith 25mc30
 

I am replacing an arched out HV rectifier socket in my Zenith 5111. The rectifier is a 3AT2. The 1.5K Ohm resistor that once resided there across pins 5 and 9 was burned in two. A very kind gentleman and member pulled a socket assembly for me from a chassis 1 year newer in which no resistor was used. This could be from a prior repair or by a change in design.

In another thread I have questioned what this series resistor actually is doing in the circuit, but with that not being the primary topic I never found out. Someone with a lot of experience in TV repair from that period said that this resistor was known to burn up and that techs often simply jumped over it. I am thinking that it may be a bleeder resistor, but it's only speculation. That would at least explain it not being essential in the circuit for operation.

I have a 1.2K Ohm 2W on the way. Easy enough to pop in just for safety and security. However, the jumper is already in place in the part coming and I am going to be working in very cramped space. So if anyone has any specific information as to the need or lack thereof as well as function of this resistor, it would be greatly appreciated. I may even need to find the correct 1.5K if it were to be a matter of critical voltages or current being spot on, but so far the information given to me speaks that this will not be an issue.

Thanks

Tube

I found HV service tips covering early Zenith color TVs in Tab Books No. 502 by R.L. Goodman, Zenith Color TV Service Manual chapter 5 page 68. It says:

"In all chassis using the 3AT2 HV rectifier, the picture may have all sorts of vertical, horizontal, and diagonal lines across the screen, plus elaborate rainbow effects. Also, there may be a loss of color, even though RF interference is not evident in the picture.
The cause, in this case, is an isolation resistor, located under the HV rectifier socket that has burnt or deteriorated. This is caused by a shorted HV rectifier. The most effective solution is to eliminate the resistor completely. Solder a wire across the socket terminals where the resistor was wired in, and replace the 3AT2 HV rectifier."

" ... check the filter resistor under the HV rectifier socket for arcing. DO NOT replace the resistor. Solder a lead-wire between the socket terminals where the resistor was removed."

"Improved High Voltage Rectifiers
(X and N Series Chassis)
Improvements in 3AT2 high-voltage rectifier tubes has eliminated the possibility of vertical streaking known as diodehausen. Thus, the 1.5K resistor in series with the high-voltage anode lead is not needed and has been replaced with a jumper wire to keep the outer shell of the 3AT2 socket at high-voltage potential."

I bought my used copy on Amazon. It covers from chassis 27KC20 through 14Z8C50, which includes the 25MC30 chassis.

Dave

Dang, I was gonna suggest jumpering that resistor out, but thought the better of it, figuring there must be some arcane reason for its being there.

Wow! This information is absolutely amazing and thanks so much Dave! If my fly is not somehow damaged I am thinking that the socket replacement that I am about to do is not only going to take away the raster distortion, but also may give me 'for sure' color as that has been intermittent through all of this. I haven't talked about it so as not to throw too much out there and confuse the main issues.

VK once again and as always has been an invaluable tool in this matter! Really, it's the members, which are some of the best people that I can imagine gathered to one place.

I should have my socket in a few days and with a little luck may have one nice playing Zenith! I will keep everyone posted if for no other reason there are more Zenith people starting to come out from behind all of the CTC repairs. Not bashing RCA folks; they just need more repair data for more repair. With Zenith the quality really did go in before the name went on!

All 'cept for their plastic efficiency coil forms.:D

You are quite welcome, glad to help. Hope it fixes your color issue.
Dave

The best part about fixing a "golden age" Zenith is that the service manuals pretty much cover every damned failure possibility, due to the fact that on the rare occasion something did go wrong, it usually involved one of the voodoo component bits. Detail is everything in terms of maximizing your revenue per lineal service-bench foot. Short occupancy is good, hangers-on for head-scratching and goose-chasing are bad. :thmbsp: When your unfamiliar symptoms are described spot-on in the book it makes you just want to hug the engineers.

I guess I will go ahead and jump over what was going to be a new resistor. Although not needed for the set's operation, I was thinking that at least it was providing a short circuit protection of sorts as they go open due to shorted rectifiers. When way more experienced techs say "DO NOT", I listen!:thmbsp:

Thanks again!

I just replaced 1.5k resistor on my 25LC20 (before reading this) old one looked all right but measured low (1.26k). Low resistance is also a sign of heat stress/damage. Maybe it's there to protect rectifier and or Pic tube or people from 22kv!

The HV rect filament wire was hardened from heat and had 1/2" bare stripped connections to socket! Who did that? Not factory?

There was a lot of wax melted from flyback!

The 2,2k final Horiz Output screen resistor looked cooked - was very high 11k! but set worked.

Will soon see if this corrects my vertical lines (is this "diodehausen"? screen picture)

Here is a picture of the Goodman manual page on the 3AT2 and HV resistor issue. Also here are the two pages of 25MC30 service notes.

Dave

I am guessing that diodehausen must be an effect similar to barkhausen resulting in vertical lines. You might want to try the Goodman suggestions posted above. They mention a newer version of the 3AT2 solving the problem.

Have you checked the HO cathode current? You mention 22KV, shouldn't that be 25KV? A lower HV setting on my 29JC20 causes the cathode current to rise.

Dave

Does the Goodman manual say anything about vert foldover?

I left the new 1.5k (2w) resistor in as it was reassembled.

Still have my H-synced artifact on screen which can be heard in speaker also, seems to be a micro arcing in some component getting into the RF then onto screen - more pronounced as you fine tune into chroma/sound

I'm the guy who's guilty of replacing the resistor on the socket I sent to tubejunke. I wanted to get it in the mail in a timely manner. I only had a 1.2K 2W res on hand. The socket I got had a jumper.
I recall, that I inquired about the resistor at the Zenith distributor. The head technician said, just to jumper it out. It's not needed anymore. That has to be 40+ years ago, before I bought the Goodman book.

Regarding the HV rect filament wire, that wire is resistance wire and probably gets warm in operation. The insulation probably receeded from the heat. That I've seen before. :scratch2:

The filament loop wire is not resistance wire.
What manner of engineer would want to squander hard won deflection power as waste heat? :saywhat:

The hardened insulation is probably from ozone.