Panasonic K Deck User Manual

VIDEO

The Panasonic K Deck

It's three years since Panasonic VCRs started to use the K deck,

long enough for a service history to be prepared. John Coombes

describes the various fault conditions he has encountered

The design of the Panasonic K deck, used in NVHD

and NVSD series models, follows the line adopted

by all VCR manufacturers in recent years, with a

substantially reduced number of parts in the drive

mechanism.

Design Features

A separate motor is used for loading and mechanism

control, with the brakes and loading gears directly driven

via a multi -function lever. There are no sub -levers or

solenoids. A tape end/beginning detector LED is used

instead of a slide switch: this reduces the wiring required.

There are fewer joint parts, and a smaller and thinner top

plate and rack.

There is no longer any take-up reel incline position or

P5 post height adjustment. Gear phase position alignment

is also reduced. The K deck has only six gear phase

alignment positions in comparison with the G deck's

twelve positions.

The VCRs that use the deck are easy to dismantle, with

the deck coming away from the main PCB. This enables

mechanical parts to be replaced very easily. To help with

fault finding, the VCR software has a built-in self -

diagnostic test system.

The Servicing Position

The K mechanism can be removed from the main circuit

board assembly, but an extension cable

VFK0889) between the loading motor and PCB socket

P2001 has to be used to maintain operation. With the deck

in the service position, its condition and the gear phase

(part no.

alignment can be checked. The loading/unloading

operation can also be checked. This can be done by

connecting a 4.5V battery across the loading motor pins,

or by manually turning the worm gear or worm wheel

gear.

If eject occurs when the cassette carriage has been

removed, on reinserting it after repair the main cam gear

will not engage with the carriage connection gear and will

not rotate. To set up the eject operation with the cassette

carriage disconnected you have to rotate the carriage

connection gear by hand in the anti -clockwise direction.

Faults Encountered

As with so many decks, the most common problem is
tape damage because of a faulty pinch roller (part no.

VXA2246). The symptom can be tape creasing or

chewing. There may also be tape looping, which can

cause damage in playback or when the tape is ejected -

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November 1996 TELEVISION

VIDEO

you can get looping around the guide poles or the pinch

roller itself. The tape can ride up and down a well

polished pinch roller, the result being creasing at the

bottom and/or top of the tape and possible damage. This

problem can also affect the sound and/or picture quality.

If there is wow on sound, or picture jitter with missing

control pulses, but no tape damage the cause can again be

incorrect tape drive because of a polished pinch roller.

If playback of a machine's own recordings produces a

noisy picture (poor sound and picture), check whether the

audio/control head is dirty. The cause of the problem is

missing control pulses. Cleaning the audio/control head

usually suffices, but on a few occasions we have had to

replace it. Although we have not had any electronic faults

in this respect, the control pulses come from pins 34 and

35 of the MN6743VRTB chip IC6001. If there is no

sound with a machine's own recordings and the output at

pins 34 and 35 of IC6001 is correct, replace the AC head.

A worn lower drum can also affect the sound, and

we've had this with a few machines. Because of the wear,

the tape wanders up and down the AC head.

Mechanical noise in the fast forward mode can be

caused by the tape itself or a faulty idler arm unit. If the

VCR won't load correctly after replacing the idler arm

unit, check that the idler control lever is correctly fitted

and is not broken - replace it if you are not sure.

If the tape becomes stuck when eject is selected, check

whether the take-up brake arm unit has come off or

broken - this will mean that the take-up reel is unable to

rotate.

If the playback picture

is

noisy, check the lead

connections to the lower drum. Be sure to check the RF

envelope. If the lead is broken, there will be no FM output

from the video heads or upper drum.

On a few occasions we have had a machine whose

playback has been spoilt by noise bars. They have been

very noticeable with prerecorded tapes, though the

machine's own recordings have been free of the fault. The

cause has been dust or dirt on the inclined base assembly
(guide poles).

Always check whether anything is obstructing the

inclined base assembly. If this is OK but the VCR goes

into the cue mode when the play button is pressed, check

whether the inclined base units (supply and take-up) are

completely locking. Ensure that the V stopper and

inclined base assembly is well greased.

If the machine won't accept a cassette, check the

cassette holder plate unit. The cause may be just a broken

release lever at the side of the unit.

If the video head cleaner arm unit is broken or

incorrectly positioned, the head cleaner can be left in

contact with the head all the time. This can result in a

very badly worn upper drum.

There are several possible causes of chewed tape,

including the pinch roller (see previous note). If necessary

check the P5 arm unit, which may be bent. This can

prevent tape ejection, with damage to the tape. Also check

P5's stopper base, which can crack. Visual inspection will

show whether either of these faults is present. If the P5

Carriage
connection gear

Fig.

1

alignment.

Rear

Front

(left):

Carriage connection gear phase

Cassette

carriage gear

Fig. 2 (right): Mode switch alignment.

post stopper retaining clip is broken there can be incorrect

mechanical functions.

If the cassette blinder flap doesn't close, check the

operation of the carriage connection gear with the side

plate unit (right-hand side). There may be a phase error

between the two assemblies. Remove the cassette unit and

ensure that the tape will go in and out of the housing

freely by hand. If this is OK, set up the carriage

connection gear as laid down in the service manual. If the

two side plate units and the carriage connection gear are

incorrectly set, the tape may be ejected immediately after

it's inserted. For smooth loading and unloading, the

carriage connection gear must be set up to fit into the

cassette carriage gear as shown in Fig. 1.

For correct operation of all mechanical functions the

mode switch must be set correctly. Set it as shown in Fig.

2, in the eject mode, so that there is a 4mm gap between
the edge of the switch and the arrow marked on the dial.

Note that if eject is selected when the cassette carriage

is not in position, when it's refitted the main cam gear will

not engage with the carriage connection gear which will

not rotate. To reset, rotate the carriage connection gear by
hand so that, as shown in Fig. 1, it's in alignment with the

cassette carriage gear.

The mode switch causes its share of problems, many of

which are intermittent. No play, fast forward in play and

no rewind for example. If any of these operations works

intermittently, try cleaning the contacts on the switch and

the PCB before resorting to mode switch replacement.

For noisy rewind and/or fast forward operation, check

that the take-up and/or supply reels are lubricated so that

their rotation is free.

Earlier Models

We've had forward visual search problems with some

earlier models, such as the NVSD30 and NVSD40.

Because of a worn lower drum unit, line lock is lost

during search. The fault has been experienced with three

and four-hour tapes. Playback and cue have remained

stable.

The cause of the excessive wear has been a broken take-

up brake arm unit. As a result the back tension is

increased. A new unit may cure the fault, but the drum

assembly will need replacement in the near future.

-

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