Job Number

0010-03

Equipment type

Television (17”)

Make + Model #

ORION – Color 517

Made in

Japan ?

Comments

Already had the same symptom, about 4 months ago, and was fixed by a simple dry joint repair

BAD

1

No power, dead TV

2

Blown mains a.c. fuse

GOOD

1

n/a

Repair summary

DEGAUSSING POSITIVE CO-EFFICIENT THERMISTER (PTC) SHORT CIRCUIT

Full repair description and observations

1

The mains fuse was blown out

2

Since previous fault consisted of dry joints in the a.c. plug connection, I desoldered and soldered some points in the power supply, including this plug.

3

The fuse was replaced (2.5A / 250V / fast blow) , powered up, but the fuse blew again!

4

Suspicion fell on a short in the Degaussing Positive Co-efficient thermistor (PTC) since it lied across the ac live/neutral rail.

a            b               c

5

The PTC was desoldered, checked its resistance across its 3 pins and compared it with a good PTC (in PCB) of a commodore 1084S monitor:

                           Suspected                                   Commodore

                             PTC:                                           1084S :

                                    a – c = 12   W (?)                         a – c = 24 W

                                    b – c = 185 W                              b – c = 1.94 kW

                                    a – b = 196 W                              a – b = 1.96 kW

6

It was concluded that the PTC was short and bought a new one

7

I replaced the blown fuse, and powered up the TV with the suspected PTC removed – the TV powered up successfully and a grainy raster was observed.

8

The new PTC was not exactly of the same dimension as the original one, it had the middle pin more near the line passing from the other 2 pins (a,b).

9

The board was drilled with the portable driller (using 1mm drill) and a link was made to the track. The degaussing PTC was soldered in place.

10

When powering up, a raster with grains with no magnetic colours was observed, TV worked perfectly.

11

Finally, the mains plug was replaced from a 2 pin to a 3-pin switchable plug.

Precautions, fouls and advises

1

 While powering up during test, the main board was not fully inserted into place, and when I pressed the ‘power on’ from the remote control, there was a spark from the aquadag graphite coating of the CRT, to either the ‘power-on’ LED or infra red sensor. This took place also on switch off – again when pressing the remote control. The spark was quite big and dangerous!

2

While I was checking the Line output transistor. It gave a minimal reading of 0.03W between base / emitter, making it appear to be short circuit. However when desoldering and removing the transistor from PCB, it gave a normal resistance reading of 50 W

3

To work properly, all connections with the main board were removed. These consisted off:

-          CRT Plate

-          EHT dummy

-          Plug from CRT plate to coils around CRT (dynamic conversion correcting yoke?)

-          Plug from main board to CRT deflection coils

-          Sound plug

-          Degaussing coils

Once, the TV was powered up, with one of the above not plugged. No fault was done, but to prevent such thing, it is advised to write all the plugs/wires/etc disconnected, marking also their position, so that none remains unplugged when testing or assembling the TV.

1

Degaussing coils resistance = 47 W

2

Line Output Transistor, b-e junction diode check = 0.041V      (removed)

3

Line Output Transistor, b-e junction resistance = 52 W        (removed)