Old CRT TV. Works a few minutes then the image becomes smaller (vertical), and disapear. I have a schemativ for a slightly different version, Vertical Deflection Output stage is very similar. It looks like the temperature of the HS of output amplifier, TDA 8172, is (very) hot. I verified the voltages, the only unusual thing could be considered the fact that +15V is only 11V. The image (while it's present) is not distorted (vertical yoke could be considered as good). All electrolytic capacitors related to the stage are in acceptable condition.
Anyone any experience with something similar?
It could be the IC, I may have to replace it to verify... or maybe just to start TV without vertical yoke connected (brightness and contrast at minimum), to see if still heats up.
NO NO NO! never ever start up the tV set without a deflection yoke connected. You can not only damage the picture tube but also the Hi voltage supply circuit.. best thing to do if the IC is getting hot is to simply replace the vertical output chip, but you could have a bad capacitor or two in the meantime. You will need an ESR type meter to varify. Good luck and let us know please how you make out with this repair.
Larry, your advice is a logic and sound one... I have to confess that I started up many times different TV sets without vertical yoke connected and I never burnt the chromofors of CRT, power supply or HI voltage supply circuit (I always took all the necessary precautions). It does not mean I would advise anyone to do the same when they do not realy know what they are doing.
I mentioned in my original post that all ELCOs are in acceptable condition (it means that I used an Agilent 4263B LCR meter - I hope you consider that one good enough), including ESR measurements. I just asked if someone had a similar experience, otherwise I know very well what I have to do.
I have the same model TV and now it's having the same problem. Can someone upload the schematics for this TV? Thanks.