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5 inch B/w Portables
Most 5" BW portables have an external power source, either batteries or a mains psu unit
when the power enters the tv/radio unit it comes thru some type of fuse/protection, then on to the power regulator
there are 2 types , 1 is an NPN and the other a PNP type power transistor.
Tracing the pcb track from the DC socket thru the fuse (if any) then onto the power transistor (with large metal cooling plate)
if it leads to the middle leg of the power transistor, then its an NPN type
if it leads to one of the other legs then its a PNP type
either way the voltage here will be the same as the psu supplies (maybe 12v)
and the voltages on 1 of the other legs should be about the same (within 0.6v)
but the voltage on the other leg should be lower (say about 2v lower)
if that is the situation , then the regulator is working ok
If not then the most likely part to go it that transistor. also check the two smaller transistors nearby
If the regulator is ok, then on to the line output stage (see cct diag below).
Note CRT heaters are usually powered direct from the main psu regulator output
( so if its glowing then psu is probably ok.)
Line stage
the line output transistor(loptr) is usually near the eht transformer(LOPTX) and has a smaller cooling plate(heat sink), it is almost always a NPN device, so the power line hits the middle leg after going thru the loptx winding
the voltage at the other two legs should be very low , trace the pcb tracks from each leg and one should go to chassis(earth) and the other to a very small transformer/coil, this is the line driver transformer, it should have about 10v on two of its legs and nothing on the other two
the most likely faults in this area are the loptx and the loptr
the next thing to check is the line driver stage, this is often driven dirctly by the timebase chip, or sometimes there is a small driver transistor between the chip and the transformer
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