Philips K35 crazy problem

[Jimmyhaflinger]

Hi,

I'm having a really weird problem with my Philips K35 set, a couple of days ago i turned it on and it only displayed the upper half of the picture, the vertical linearity was perfect, but the bottom half of the picture was black.

I turned up the A1 controls and the raster is filling the whole screen, but still only the top half of the picture is being displayed!!
how can this be possibile

[Peter.N.]

Sounds like a blanking fault, I don't really remember this set very well but I would check the frame IC for dry joints. I'm sure someone who knows will be along in a minute.

Peter

[Heatercathodeshort]

Hello Jimmy,
Sounds like a cap in the blanking circuit. I can't tell you which one as it is a very long time since I serviced a K35 for a customer. Worth also checking if the socket for the colour/luminance chip is still in place. If so I would remove it and fit the chip direct to the P/C board. You may have to 'Q' the pins. Hope this helps. John.
Sorry Peter! Just seen your post. Must have been writing at the same moment.

[jayceebee]

Definitely blanking problem, my first check would be the IC sockets on the teletext decoder. Removing and refitting the IC's should clear the fault for a while, as per John HKS remove the sockets and solder the IC's for a permanent fix.

[Sideband]

Something in the back of my mind is telling me that this is a diode in the blanking circuit. I've seen this fault and fixed it but it was probably 20 years ago. I no longer have any information on it. I keep seeing a little brown diode with BAX14 on it saying 'change me, change me'.........!



SB

[ben]

I had this in an old blaupunkt of that era. thyristor problem I think, or try reinserting the deflection daughterboard(s)

[Michael Maurice]

According to Euras

change C588 680µF, also check resistor R520

[Jimmyhaflinger]

I've done some work on the K35 set today, apparently, the blanking pulse is derived from the frame output stage, then is fet to the base of Q535 then it gets to pin 9 of the chroma/luma board, i checked with my scope and i'm apparently missing the blanking pulse from the frame output, i just have a clean sawtooth with no blanking pulse (or maybe it's too narrow to be displayed on my scope?)
I also have a clean sawtooth on the base of Q535 but there's a sort of distorted square wave on its collector... i replaced this transistor but this made no difference...

[Welsh Anorak]

Hi
I think I've only had this once and it was a capacitor in the frame stage, though of course I can't remember which! I'd start as MM says with C588.
Glyn

[Jimmyhaflinger]

the problem was actually C588, it literally fell apart when i removed it. the set is displaying a full picture now.

I had some trouble to find C588 as i expected to find it near C589 in the frame stage, C588 was on the other side of the chassis in the line output area instead!

[Jimmyhaflinger]

The set is back on the bench! this time for a different problem though...

I turned it on last night and it displayed a narrow picture with no E-W correction at all,
I'm working on it now, i replaced TS490, the E-W correction transistor, then i tried to resolder D562 and it split in half.

With both parts replaced the set is now displaying a slighly wider picture but still no E-W correction...
Is there anything else to check before i take the set to the tip? i'm beginning to feel a bit frustrated with this set...

[MALC SCOTT]

Check the e/w loading coil. Could be s/c.

[Welsh Anorak]

Hi
Also check that big capacitor under the LOPT for dry joint or O/C. Then short B/E of the E/W transistor to see if the scan jumps - if so then it's likely to be the drive transistor. Good sets these - rarely any frame or E/W faults! Until now...
Glyn