so, the 4900 in my satan's hollow needs to be capped. however, i can't get the focus completely good in it's present state, just close to clear but still slightly blurry..... i know in a g07, etc, this is typically indicative of a dying fly, but wanted to clarify i'd need one on the 4900, or if just capping it will take care of it... note - i haven't checked my b+ yet as i thought it was a g07 until i looked closely at it. is it possible that if the b+ is low it may clean up the focus issue?
k4900 flyback and cap kit question
- Thread starter cleverlyj
- Start date
modessitt
Volunteer: Encyclopedia Submission Moderator
Maybe.
Bad focus can be the result of:
a) dirty tube/bezel
b) cold solder on the neck socket focus pin
c) bent or dirt focus pin not making good contact
d) bad burn-in
e) old tube
f) bad flyback pot
If the high voltage is coming out okay, and just the pot is bad, or unable to comletely focus it, I wonder if you could put a resistor or another pot in the output feed to the focus pin to give you a different range to dial it in better.
Now, if it gets better then worse when adjusting, but the "best" just won't focus perfectly, then it probably isn't the pot. If you turn it all the way one way and it was getting better but you can't turn the pot anymore, then maybe the B+ or pot is your culprit...
Bad focus can be the result of:
a) dirty tube/bezel
b) cold solder on the neck socket focus pin
c) bent or dirt focus pin not making good contact
d) bad burn-in
e) old tube
f) bad flyback pot
If the high voltage is coming out okay, and just the pot is bad, or unable to comletely focus it, I wonder if you could put a resistor or another pot in the output feed to the focus pin to give you a different range to dial it in better.
Now, if it gets better then worse when adjusting, but the "best" just won't focus perfectly, then it probably isn't the pot. If you turn it all the way one way and it was getting better but you can't turn the pot anymore, then maybe the B+ or pot is your culprit...
thanks for the info, steve! which pin on the neck socket is the focus pin, and also, can you tell me where to test the b+ at and what it should be set at and where the adj pot for it is? i can't find it looking at a manual online.
and also,what does the black level do? is that a contrast thing?
and also,what does the black level do? is that a contrast thing?
modessitt
Volunteer: Encyclopedia Submission Moderator
Okay:
That's the one inside the slot on the neck/socket.
There is a big white resistor mounted on the outside of the left wall in the back.
The side closest to the fuse should read +130vdc.
If you look at the pots on the edge of the board, you'll see two that are set behind the others on the left. The one on the left adjusts the B+.
Pretty much...
That's the one inside the slot on the neck/socket.
There is a big white resistor mounted on the outside of the left wall in the back.
The side closest to the fuse should read +130vdc.
If you look at the pots on the edge of the board, you'll see two that are set behind the others on the left. The one on the left adjusts the B+.
Pretty much...
ok, so the b+ measures 157v, which is very bad. but, the pot which i thought was the b+ adj is actually the horiz. hold. can someone tell me which it is or post a pic, that'd be mucho helpful.
KenLayton
In Memoriam
IC501 (STR381) is the voltage regulator. There is no B+ adjustment on a 4900 series.
Bad focus is because the flyback's focus voltage winding goes bad and can't put out a high enough voltage (too low).
Bad focus is because the flyback's focus voltage winding goes bad and can't put out a high enough voltage (too low).
so if my b+ is reading 157v, then, what can i do do lower that? replace the flyback, or are there any other options.
modessitt
Volunteer: Encyclopedia Submission Moderator
1) first check for bad solder along the back edge of the board, especially around the jumper J33 and that big power resistor.
2) If that looks okay, or if you fix some stuff but it doesn't help, check for cold solder around the flyback. Also, check closely for any tiny cracks in the board around the flyback. You might want to do continuity checks to see if each pin of the flyback has good continuity to the farthest point on its trace.
3) If nothing above fixes it, check the voltage on the outside casing of Q352 (your HOT). If it's 0vdc, then you need to go back over your areas you checked above for bad solder, broken traces, or bad parts. If you still get about 160vdc, then you should check Q351 and R363. Also, you may have some cold solder or bad traces around T351....
2) If that looks okay, or if you fix some stuff but it doesn't help, check for cold solder around the flyback. Also, check closely for any tiny cracks in the board around the flyback. You might want to do continuity checks to see if each pin of the flyback has good continuity to the farthest point on its trace.
3) If nothing above fixes it, check the voltage on the outside casing of Q352 (your HOT). If it's 0vdc, then you need to go back over your areas you checked above for bad solder, broken traces, or bad parts. If you still get about 160vdc, then you should check Q351 and R363. Also, you may have some cold solder or bad traces around T351....
thanks, ken and steve. will yank the chassis in the am and take a look at it.
KenLayton
In Memoriam
Test point 91 on the schematic is the B+ measurement point. It is supposed to be +130 volts DC.
If too high then the regulator is bad.
If too high then the regulator is bad.
Did you take that reading at the big resistor? If so, maybe you used the "wrong" side of the resistor. Take your reading at the other side and report back.
Edward
ScumBum
Well-known member
This is a great thread because I'm having the same exact problem . I got a cap kit thinking that would fix the focus problem but I see theres more to it .
Dokert
Well-known member
If you are having a focus problem Joey, check the focus wire. It is the wire that goes into the neck socket from the fly. The cover on the neck socket comes off, usually if you squeeze it together.
ScumBum
Well-known member
Ok I'll check that wire out ! Thanks for explaining where the neck socket is . You know too well I would have gotten lost trying to find it .
