These are strange after regular cassette separates
where to disassemble it's usually case > bottom panel >
knob caps > front panel > transport, here you need to
remove the slider caps and then use an angled
screwdriver to remove two screws in the cassette
compartment. Then turn the unit over and remove the
plywood bottom and then 6 screws holding the chassis
into the case. Once the chassis is free you have to
gently ease it out from the case so that work can start
work on disassembly and removing the rubber parts.
Notice I've got a rubber anti-slip mat underneath.
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Underside view with bottom cover removed. Click on image
for larger version |
One of the first things you need to remove are the
tape counter belts and the spools, here the belts are
easy enough to remove, the small counter one is falling
off anyway. Sometimes the spools are held on with
miniature circlips or nylon washers, here they're held
on with plastic caps which needless to say are virtually
impossible to buy now and need to be removed gently
- they are delicate enough when new, after 35 years you
need to be very careful. There's a rubber tyre on each
spool which needs to be removed and measured up for a
new one.
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Close-up of transport showing spools, heads,
pinch roller. Click image for larger version |
Now for the central idler wheel. This is delicate
and obsolete now so it needs to be handled carefully,
there's a circlip holding it on which will need to be
removed first. The idler is in two sections, each with
an idler tyre and it also has a little fabric clutch
disc in the centre section to act as a slip when the
spools reach the end of a tape. The two tyres are the
same size and difficult to remove without cracking,
better to cut the tyres neatly with a scalpel than to
risk cracking the idler. Also the pinch roller is now
removed, the metal holder is held in by a circlip and
the tension spring unhooked and the holder removed,
apart from being coated in tape oxide the roller looks
ok but I have a new one so it will be replaced
regardless. Originally, the entire holder assembly would
have been replaced but Pioneer likely stopped stocking
them a long time ago so the roller needs to come out and
a new one be installed in the original holder. The axle
needs to be tapped out carefully with a centre punch
from the rear side and the roller removed. The axles are
a tight fit and sometimes need a lot of force to remove,
be careful not to damage the holder while doing this.
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Close-up showing take up spool and central
idler. Click image for larger version |
Deck is now turned over to remove the main drive
belt, three screws holding on the flywheel backplate and
you'll need to also loosen the bracket for the playback
switches. Refit the bracket afterwards to hold the
flywheel in place. Belts and tyres are now removed and
can be measured up for new ones. The whole mechanism
needs gently cleaning and any old grease removed and
replaced with fresh, one thing to mention is the two
ball bearing guides over on the front side for the head
assembly, there's a screw holding the cap on each then
each bearing can be removed and regreased. Be gentle,
these bearings are very small and easily lost.
Also the two heads themselves need to be cleaned with
isoprophyl alcohol (IPA), take care not to scratch them.
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Underside of transport showing belt and
flywheel/cover plate. Click image for larger
version |
Now the electrical work starts, before you start
you need to work out the order in which you'll work.
I'll solder all the tie wrap pins as I go and inspect
everything for bad solder joints and pull a dozen or so
capacitors at random and test them for value and ESR.
First is the main Dolby control board, it's held by two
screws and is then gently swung over to be soldered.
Then the little regulator board, I replaced the
capacitors on there although the originals tested fine.
Then over on to the main board, this is a tricky one as
you need to be careful of the main switch fingers
fouling the two main record/playback switches and
there's a lot of wiring snaking around which is easily
broken.
While you're in here resoldering the many tie
wraps, it's a good idea to clean the two switches as
they're near impossible to reach once the board is back
in place. Sliders can be accessed from the front so
leave them alone at the moment. The main switch PCB is a
pig to get to and too much wiring snaking around to
remove it without cutting looms. I had to remove the
fuse PCB and push it and a lot of other wiring aside to
get in here safely to solder without stubbing and
melting the wiring. I'll be putting a new mains lead on
so now's a good time to remove the old one and remove
the switch to solder the new one on, once the boards are
back in it's impossible to get to. Also it's worth
mentioning that the most important parts which need
soldering - the ground tags - are tucked away behind all
the wiring and are easily missed. There's two sets of
tags here, one for the audio sockets and one for the
ground wiring in general, all connections need to be
soldered to eliminate any chance of noise or hum later
on.
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Close-up of regulator board showing new
capacitors (L) and also main board (R).
Click images for larger version |
Things are now coming together, the remainder of
the switches now need to be cleaned and oiled, there's a
few in different places which need to be found. Also any
parts still attached to the chassis need to be cleaned
(tape buttons, headphone sockets, switch caps), if you
use water be careful it doesn't get into the circuits.
The case is now cleaned gently in warm soapy
water, this takes a time to do properly and get 30+
years of grime out of all the nooks and crannies.
Just don't literally soak it in water and also be
very careful of the faceplate lettering, the lettering
is only printed on and will start to loosen if left to
soak too long. The end result should be good, the best
its looked since 1974. The cassette door was broken,
somebody before had attempted a decent repair, likely
the only time the deck has been opened. One of the lugs
where the door attached to the axle was broken, as the
replacement part has long been unavailable the best
repair for this is to mill out a pair of channels and
shape a piece of 1mm tinned wire to fit in like a
staple, the wire is elbowed at each end to fit into 1mm
holes drilled into the plastic for extra strength.
Another reason for using a metal staple is it's easy to
reshape to make minor adjustments afterwards for square
fitting. Once bonded and left to set it makes a very
strong repair and the door works like new and sits
straight on the case for the first time in years.
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Cassette door repair, tinned copper 'staple'
replaces broken hinge and is crimped in the
centre to allow adjustment, not terribly
neat but will be hidden and makes a good
strong repair. Click image for larger
version |
Now the reassembly starts, any boards are gently
screwed back into place and wiring rerouted and
assembled with new wire ties. At this point the new
mains lead is fitted into the rear of the chassis with a
new grommet and the fuses replaced with new. I also
resoldered the connections to the fuse PCB, the wires
are quite thin and tend to break off at the solder
joints. Idlers and spools now have their new tyres
fitted and belts and new pinch roller are also installed
once the parts have been degreased with IPA.
Back to the top, the VU meters are held in with
foam padding, after 34 years this has rotted and the
meters are now loose. Good quality foam like that used
to pack computer motherboards makes a good replacement
once traces of the old are removed. The old foam is
difficult to remove once it's degraded, sometimes it
just crumbles but sometimes it becomes a sticky mess
which could best be described as a chemical version of
sticky ginger cake (as is the case here). The meters are
illuminated by a single 8v lamp and sit in a white box,
over time the white card has badly discoloured. We
could paint it but I'll cut some white laminate and
paste it on with contact adhesive and clamp it until
dried, this will make things nice and bright again.
Now is the time to triple check everything and
apply power, if all goes well first time around it's
time to test all the functions are working and then tune
the tape speed, playback/record levels etc. It's always
wise to have a small stock of 'disposable' cassette
tapes when testing a deck, with the best will in the
world the first power up of any equipment after work
carries a small risk and a slightly misaligned
playback/record switch or pinch roller could mean your
favourite album gets erased or chewed up. Once we check
everything is working correctly, we can start re-tuning
all the levels. Cassette speed and head azimuth needs to
be tuned first and ideally before the chassis is
reinstalled back into the case because although the
playback level pots can be tuned from underneath with
the bottom cover removed, the cassette speed was tuned
in the factory through a hole in the top casing which is
now covered by the aluminium trim panel.
And the end result, some glamour shots of our
newly restored CT-5151:
