PR603 PR703 PR903 PR1000 Main Boards also PR602 PR702 PR902 Main boards

General and additional info about removing the main board from these pianos.
NOTES – PR602, 702, 902 main boards can be removed in a similar way but the connectors are in different places so this description does not apply except for “the unusual white connector”.
The PR602 main board is covered by a screening card which must be removed first.
PR604, PR804 – at present I cannot test main boards from these but I can repair and test the amplifier boards.

Thinking about the countless times and ages I’ve spent on the phone telling people how to do this, I really should have written it out before.  Oh well ….

Read all of this before you start.

Read the sections of my Technics page
If opening piano to remove circuit boards” and
Tips for removing circuit boards” and also
Packing” and “Shipping method

Unplug the piano before opening it please – I can’t do repairs for dead customers!

Make drawings or take photos and make good notes so you can refit everything correctly.

NOTE:  my description assumes you are standing in front of the piano

1 – make sure the piano really is unplugged from the mains!

2 – take top off piano – I don’t know about PR1000 as I’ve never seen one
Don’t try to remove the back of the piano
Four screws on back of piano in a row near the top, then knock top forwards, then lift off
Slide keyboard cover shut over the keys so you can see inside the piano

3 – do drawings or take photos and make notes of where connectors go

4 – unplug main board connectors – see description below

5 – remove screws – see description below

6 – get the board off its mounting posts – see description below

Again, my description assumes you are standing in front of the piano

PR703, PR903, PR1000 only.  Look carefully at two connectors near the front left-hand corner of the main board.  It is possible to get these mixed up when replacing the board.
Smoke will definitely come out of the MAIN VOLUME if you mix up these connectors!
They are the same size and each has the same type of grey ribbon cable.  One grey ribbon cable is longer than the other and goes to a connector part way up the left edge of the board with VOLUME printed on the board beside it.  The shorter grey ribbon cable has a piece of green tape around it and is plugged into the leftmost connector on the front edge of the board with MIC printed on the board beside it.
Most of the connectors (including these) unplug by firmly holding and pulling upwards the bunch of wires which come up out of the top of each connector.
DO NOT try to unplug these connectors except as described.

PR603 has no MIC connector so it should have only the longer grey ribbon cable which goes to the VOLUME connector.  However, making notes and taking photos is still a good idea.

Each of the other connectors is a different size so it’s pretty hard to mix up these.

The rear edge of the board has five connectors on the board itself but only three are used.

Most of the connectors unplug by firmly holding and pulling upwards the bunch of wires which come up out of the top of each connector.

Connectors with more wires are harder to unplug.  Don’t jerk the wires upwards.
Use what I call controlled force.  Try to avoid one end of a connector becoming unplugged suddenly as this can bend the terminal pins at the other end.
If this happens, don’t try to straighten the pins.  I will do this.

The wires from the floppy disk drive loop through a black P-shaped thing which is screwed down close to the board.  Unscrewing the black P-shaped thing makes it easier to unplug this connector.  For those of you who like proper technical terms, the black P-shaped thing is an inductor or choke.  Whatever you call it, it still gets in the way!

One small connector near the front right-hand corner of the board has its wires coming out of one face of the connector i.e. not out of the top.  This is easy to unplug by holding the whole connector body (including its wires) between finger and thumb and pulling upwards.

There is one unusual connector about halfway along the left edge of the board.  It is white.  On the right side of this connector is a small white tab (part of the connector) sticking out to the right.  Put your finger under the tab and ping or pluck it upwards.  If it doesn’t unplug at the first attempt, try again.  Surprisingly, you can actually break a fingernail doing this! When you have unplugged the connector, plug it back in again by pushing it down firmly several times with your thumb. You should be able to see that it is lined up properly before you plug it back in. Unplug and reconnect it a few times until you are familiar with it. This will help when you are refitting the board.

If this board has not been worked on before it will have two black earth (ground) wires.  These are soldered to the board near the front edge and are screwed down to the main shelf of the piano.  Remove the screws.

Also, if this board has not been worked on before it will have three earth (ground) brackets which are silver colour metal.  If present, there is one near the rear left-hand corner and two on the right-hand edge of the board.  They are soldered to the board and screwed down to the main shelf of the piano.  Remove the screws.

To avoid these earth (ground) brackets getting broken off in transit I usually make a half-inch thick pad of anti-static bubble-wrap and place it under the board before wrapping the whole thing in more anti-static bubble-wrap.
NOTE – anti-static bubble-wrap is pink or blue.  Don’t use clear bubble-wrap for this because it is not anti-static.
If the brackets do break off I can refit them.  Quite frequently I get sent boards with no brackets at all, and sometimes earth (ground) wires missing.  Presumably these have come adrift and not been replaced during previous repairs.  The board will work normally without these and I am not aware of it having caused any problems.

Remove the two screws going through the two rear corners of the board.

Now for the “fun” part … getting the board off its mounting posts.
The board is mounted on five nylon posts which are a very tight fit
Each nylon post has flared-out bits which must be squeezed together using long nose pliers whilst you try to ease the board part-way up the post.
Instead, work your way round the posts, easing the board a little way up each one in turn.
Take care that your long nose pliers don’t skid off a mounting post and damage any circuit tracks on the top side of the main board.

Packing – Pack the board well. The box you use should be large enough and strong enough to protect the board. DON’T USE A JIFFY BAG!!
Main boards – use a box deep enough that the board won’t get crushed and large enough that the board is not a tight fit. A shallow box is no good.
Amplifier boards – a shoe box is about the right size for this – deep enough and quite strong. I would use several layers of bubblewrap laid flat first. Place the board on this flat bed of bubblewrap and then add bits of bubblewrap or loose-fill on top. Don’t squash this down hard on the board. You just need enough to stop the board moving around.
If sending both boards pack them very carefully so they cannot damage each other.
It is possibly a good idea to face the undersides of the boards towards each other because the undersides are fairly flat. Use sufficient packing between the boards.
Maybe pack the main board it its own box to protect it better but not in a shallow box.

When refitting the main board take care not to trap any wiring or connectors or the black earth (ground) wires underneath it.
Push the board on to its nylon mounting posts until fully seated.
PR703, PR903, PR1000 – DON’T mix up the VOLUME and MIC connectors! See earlier note about this.
Make sure each connector is firmly plugged in, especially the white one half way up the left hand edge.
Refit all the screws correctly – DON’T DO THIS WITH THE PIANO SWITCHED ON!