[torbjorn]

If you look at the datasheets, you will see that although the two parts are similar, there is one major difference. The TDA8170 has an internal reference voltage connected to the non-inverting input, pin 7, so that pin only needs a decoupling capacitor to ground externally. The TDA8172 does not have an internal reference voltage so it is the responsibility of the equipment designer to connect a suitable voltage to that pin.

Generally, if you find that a vertical output amplifier does not work properly, check the supply voltage and check that there is no short circuit in the deflection coils or electrolytic capacitors around the amplifier.
Also, beware of flashovers from horizontal to vertical deflection coils, the high peak voltages at the horizontal coils could easily destroy the vertical amplifier.
High voltage flashovers internally in the CRT can also induce high currents in the deflection coils, causing similar faults.

[jts1957]

Put the SAME number part you originally took out of the unit, back in.
If it fails ... you are overlooking something.

[thefixer]

Hello evry one ,i bought tda8170 but i find it corrupted even it is new.on ther part i have good tda8172 .can substitute it with tda8172. i checked diagrams of every chip i find them quite similar .can any one help me to solve this?THANKS IN ADVANCE.