K7131 vertically squished picture. What could cause this?

[action76]

Got this K7131 with a badly compressed / squished image. I recapped it with no change. What can cause this and what do I need to check?

[grantspain]

deflection yoke could cause that, rare but seen it a few times

[Ken Layton]

Bad vertical output IC.

[lilshawn]

failing vertical IC and bad power feed resistors to the IC.


failing IC causes extra load on resistors and causes them to drift up in resistance... going up in resistance causes the voltage feeding the IC to be low... causing the load to go up in the IC causing the resistors to get worse... (repeat until failure)

you may as well replace the capacitors as well if they haven't been done already. this chassis is pretty old now.

[action76]

Yeah I have already recapped it.  So do you suggest replacing some resistors as well when I replace the vertical IC?  If so which ones?

[lilshawn]

check:

R91 - 1.2 ohm 2 watt
R117 - 680 ohm 1/2 watt
R83 - 680 ohm 1/2 watt

if out by more than 5%, replace

also check diodes D13, D25

double check replacement of C48 C50

if picture is still squashed after replacing IC3, check for 24VDC on anode of D25... if low, go backwards through the circuit and find out what's dragging it down.

[action76]

Thanks for the info Shawn!  I am about to leave for TPF so I will have to try all this when I get back.  I will report back on my findings when I can.

[action76]

Well now I am thinking that it has to be the yoke.  I tried another known working K7000 with this tube and the picture looked the same.  What causes a yoke to go bad and can it be repaired?

[grantspain]

corrosion internally- seen it a few times, it was quite obvious from the photo( not being smug) as you can see its far more than a vertical failure- the convergence is all over the place as well
don't even bother to try to repair the yoke, you can find replacements on ebay and loads will fit that chassis. k7000/k7400/u5000/u2000- just make sure its for a 25 or 27" crt

[action76]

Ok. Thanks for the reply.  Corrosion totally makes sense because the cab the monitor came out of looked to have been in a damp environment and it had some kind of whitish powdery substance all over the metal parts.

[grantspain]

there is the exact yoke on ebay atm for a very reasonable price

[action76]

Thanks! I will check it out.