Job Number

0010-05

Equipment type

Video home recorder

Maker + Model #

NATIONAL PANASONIC  NV-730

Made in

Japan

Comments

Old type of recorder with Short / Long play option. One of the first video recorders.

BAD

1

The ‘power on’ LED lights up for few seconds than goes off and the video is completely ‘dead’.

2

No light logic display on panel.

3

Video tape can’t be loaded in.

GOOD

1

Repair summary

OPEN FUSIBLE RESISTOR IN POWER SUPPLY

Full repair description and observations

1

The first suspect was a fault in the power supply. This was disassembled from the video for proper testing and investigation.

2

The unit could not come off from place due 2 sockets soldered to the board. Since these were not plugable, they had to be desoldered out.

3

1 of the sockets (10 pin) was the voltage output to various parts of the video. The video was powered and the voltages at each pin were measured. The results are shown:

Pin 1

12V dc

Pin 4

0 (Ground)

Pin 7

0 (Ground)

Pin 10

6.4V ac

Pin 2

21V dc

Pin 5

0 (Ground)

Pin 8

1V dc (?)

Pin 3

18V dc

Pin 6

-1V dc (?)

Pin 9

1V ac (?)

4

Pin 6, 8 and 9 were suspicious since of the low voltage they were delivering.

5

On following the track, it was noted that pin 6 and 8 where coming from the same parent branch in which contained a fusible resistor in series with the mains transformer.

6

The resistor read MegaOhms, where it should have been 4.7W! Also there was 60V on one side, and 1V on the other side of the resistor.

7

The 4.7W resistor was desoldered and gave an infinity resistance reading.

8

It was replaced by a new 6.8W fusible resistor, and  a –57V and 57V were observed on pin 6 and 8 respectively.

9

The sockets were soldered back into place, the power supply was assembled back, and on powering on, the video operated perfectly.

Precautions, fouls and advises

1

While removing the power supply, it got blocked by a 2 sockets (one being 2 pin, and the other being 10 pin). These had to be removed. It was assumed that these were as usually, plug type sockets, and can easily be unplugged. However I discovered that they are directly soldered to the board. Excessive pressure and tampering could have cause further damage to the socket.

2

With some lack of attention, I risked an a.c. mains electrical shock! I removed the video from the mains, to insert the a.c. operated soldering iron. When I grabbed the power supply I got a feeling of a shock at my hand and so I dropped it back on the table. I looked at the a.c. mains plug and found out the video was plugged in, not the soldering iron! With carelessness I re-inserted again the video plug instead the soldering iron.

1

Voltage supply outputs via socket PB1 (10 pin)

Pin 1

12V dc

Pin 4

0 (Ground)

Pin 7

0 (Ground)

Pin 10

6.4V ac

Pin 2

21V dc

Pin 5

0 (Ground)

Pin 8

57V dc

Pin 3

18V dc

Pin 6

-57V dc

Pin 9

1V ac