Technics spares, spare parts

Have all sorts of Technics spares – parts from old keyboard assemblies, keys, hammers, fulcrum blocks and other bits and pieces for
SX-PX series of pianos
SX-PR series of digital ensembles
SX-KN series of keyboards

It is unlikely that I would have any circuit boards for sale because I usually manage to repair those that are sent to me.
Incidentally, there’s no such thing as a “new” board for an old model because any spare boards were manufactured at the time of production.
Companies don’t rejig to make new boards for old models. If they did, the price would be astronomical!

I can usually repair corroded boards too as long as the corrosion has not got inside a chip which is no longer available.

If you need other replacement parts I might have them to sell.

The part numbers in the service manuals can be a bit confusing
Example 1) The service manual for the original versions of SX-PR350 or SX-PR250 says
Hammer (White Key)  QMWG9005AA
but the number moulded into the body of the hammer says QMWG8001
Technics database does not find QMWG8001 – nor does the internet until it finds my page!
Later versions of these models used a different keyboard assembly which had different hammers.  You must use the correct part!
Example 2) The service manual for one SX-KN series keyboard says
C/F key is part number STBG1100A
The number moulded into the plastic of the key says STBG1100
In later KN models this part number became STBG1101A
The last number Technics used when keys were still available was STBG1101AK
The number moulded into the plastic of the key says STBG1100 but with the last zero crossed out and a number 1 above it.
Example 3) Many part numbers have suffixes like AA, AB, BA etc.
I think these just denote the period of production.

So, instead of buying a service manual it is best to look at the number on the part itself.  The service manual will give you a number which may or may not be recognised.
Unfortunately nearly every part is now listed on Technics database as “discontinued without replacement”.  Don’t despair – I may have the parts!

Nearly all Technics plastic parts have the part number moulded in somewhere.
The number might be very small so use a torch and a magnifying glass.
Nearly all Technics metal parts have the part number stamped into the metalwork somewhere.

I know many of the parts for various models already but it’s not a bad idea to give me the actual part number moulded into the key or hammer from your piano. Then I can be sure of supplying the correct part if I have one.

Chips, ICs, Integrated Circuits

NOTE – this section is only intended for service engineers and technicians who are used to working with surface mount chips and are very good at it!

Many chips have been produced in several different packages.
The correct chip in the wrong package will not physically fit on the circuit board.
To know if I can supply the correct part I need all of the info below.
1 – the model number of the piano
2 – which circuit board (get the part number from the service manual or find all the numbers printed and written on the board e.g. QJBGxxxxYY.
Usually QJBG is printed in white and “xxxx” is four numbers printed in white.
“YY” is two numbers written or stamped in black ink – not always found immediately after the QJBGxxxx but usually fairly nearby.
3 – the chip number printed on the board e.g. IC2 or IC17 or IC30 etc.
4 – all the numbers printed on the chip itself.

Enquiries without enough information will not get a reply!

All Technics custom chips with any sort of program written in are discontinued.
Waverom chips are a typical example – some are used in only one or two ranges of models – many are unique to only one range – many are unique to only one model.
They are not interchangeable and there are no substitute parts.
Only the correct waverom will work correctly.
The wrong waverom will either stop the piano working or will sound so terrible that the piano is unplayable.

All Technics tone generator chips are discontinued.

I still have various chips but ….
Some would have to be removed from untested circuit boards.
A few are new so should be perfectly ok.
There is no way of testing these chips without fitting them to a working board for which I have a piano in which I can test it.
Most of these chips are surface mount so I would have to remove the relevant chip from a good board, then remove the relevant chip from the untested board and then fit that chip to the good board for testing.
If it works ok, I still have a good board and could sell you the first chip I removed.
Not a terribly quick or easy job so the price would reflect this.

I have no way of knowing whether you fitted the chip correctly or damaged it physically or by static discharge. Also I can’t be certain that your diagnosis was correct. There might be other faulty chips and/or you might be changing a chip that wasn’t faulty.

Consequently all sales are non-refundable.

To be honest, it would be better to send me the board.
Although I can’t always promise to fix it, at least I won’t damage it.

A nasty example – PX226 with damaged pedal lead which shorted out 5 volts on the main board.

NOTE – on most main boards, if the 5 volt regulator goes short circuit (for any reason) this can short or damage any of the chips on the 5 volt rail. If the 5 volt rail still reads short circuit after removing the relevant regulator components, you’ve got trouble!
BTW don’t remove the choke – it’s a waste of time because it’s in series with the 5 volts, not across +5v and 0V which would short it out! I’m amazed at how many repairers do this.
Finding which chips (and even which chip capacitors) have gone short can take a long time.
If a chip has several legs connected to +5 volts or to 0 volts, it’s usually better to completely remove it rather than trying to lift all the legs going to one polarity.
I leave the chip capacitors to last because, although they are easy to remove from the top side of the board, they are more fiddly to refit than a chip.
I always try chips on the top side of the board first because all the components on the underside are bonded to the board with epoxy which makes them much harder to remove – and much harder to remove without causing some damage.

By now you’ve probably come round to thinking that sending me the board would be the best bet!

Back to this PX226 – removed shorted regulator components – the 5 volt rail now not reading short circuit so replaced shorted components with new ones. Tested. Piano now works but sounds absolutely dreadful. Sends MIDI ok so CPU probably ok. This board uses two identical tone generator chips and two different waveroms.
All these are discontinued. I could try changing the two TG chips (180 pins on each chip!) by removing ones from some good boards. If this doesn’t work it’s probably one or both of the waveroms. At this point I would have to give up but still have to remove my two TG chips and fit them back on my good boards and re-test those! It would make more sense to first check the customer’s TG chips to see if they are ok but this would mean fitting each to a good board and testing it. Ideally this would be a board which uses only one TG chip so it can be tested individually. On a board using two TG chips, I reckon that if only one TG chip was damaged it would still make the piano unplayable.
Eventually I’ll find out the answer to this but it will be an extremely long-winded process!

Note – the two waveroms in question are only used on PX224, PX226 and PX228 so it would not be possible to repair this piano without finding a working one of these for sale reasonably cheaply and not too far away. It could be months before one came up for sale and then travelling to collect it and cannibalising it for parts would be crazy unless its cabinet was badly damaged! It would be simpler to give up on the job and tell the customer to buy themselves another piano.

I keep telling myself “don’t despair until you have to – the waveroms may have survived.”

More info about waveroms …
The programming can only be carried out by someone who has stock of the unprogrammed chips, an EPROM programmer with sockets for these surface mount chips and, of course, the programs for the waveroms.  There’s not much chance of anyone still having stock of the blank chips – the ones I’m thinking of are a Hitachi product manufactured about 20 years ago.  It seems pretty unlikely too that anyone who owned a suitable programmer would also have gone to the trouble of removing these surface mount chips to read and save the programs.  
Afterwards they would have had to refit the chips to the circuit boards.  No-one is likely to have bought programmed waveroms from Technics because these parts are very reliable indeed.  It is crazy to have money tied up in stocks of parts which in all probability will never be needed.

Meanwhile back in the real world of “can we repair it or not?”, if a board needs a special chip, no-one can repair the board unless they have the right part.

Chips occasionally fail just because they’ve decided to, sometimes because of a lightning strike or because of a damaged pedal lead.
The models most likely to be affected by pedal lead damage are
SX-PX 222, 224, 226, 228, 552, 554
As said above, if a waverom gets zapped the board may well be unrepairable.

This is a very good reason to make sure that your pedal lead doesn’t get damaged.

There are two common ways that pedal leads get damaged.
1) the lead was trailing on the floor and the piano was dragged across it
2) the piano was pushed back too hard against the wall behind it –
this can also damage the socket which the pedal lead plugs into.

Possible disaster stories
A while back I had two main boards, both with short circuits caused by damaged pedal leads.
These boards had been to other repairers before they came to me.

One repairer had realised the +5 volts rail was shorted out but had started trying to islolate the location of the short circuit by cutting tracks.  This is NOT the way to do it!  The tracks for +5 volts and earth (ground) go all over both sides of the board.  There are dozens of connections through the board too.  It would be almost impossible and extremely messy to try isolating a short circuit by cutting tracks.  Luckily this repairer had been very sensible and given up early on, so there wasn’t too much for me to tidy up.
Result – another repaired piano and a not too happy customer who had paid for the first repair attempt and then paid for me to test, tidy up and repair the board.

The other repairer should give up forever!  Why?  Read on …
A quick but sloppy way of checking if a 2-legged component is short circuit is to cut one of the legs (much nicer to desolder it and lift the leg out of the board) and then meter across it.
This person obviously has no common sense because they cut both legs.
They had made a fairly average job of soldering this diode’s leads back together.
The best thing they did was to find that the regulator transistor was short circuit.
The worst thing they did was to try replacing the regulator transistor.
This is a very, very simple and easy job IF YOU KNOW WHAT YOU’RE DOING!!
In my opinion this person must either be blind (and you don’t find that many blind people using soldering irons) or very stupid or both … I could say clumsy and ham-fisted but I won’t – not out loud anyway.
The sequence of events and the resulting mess were as follows:
They removed the transistor and whilst doing this
1 – ripped out two of the three through-hole platings
2 – ripped off two of the circuit tracks on the underside of the board
3 – apparently did not notice this damage! (How could you NOT notice??)
Fitted a new transistor in an interesting new way
How?  Just one leg soldered …. why was this?
A lot of solder had been used to TRY to solder the other two legs
Surely it must be pretty B***** obvious that you can’t solder to bare fibreglass …..
it has to have at least SOME copper left on it!
The transistor survived.
Unfortunately I expect this so-called repairer did too.
Oh Crikey!  Hope I didn’t just insult the owner – I’ll never get paid!

Incidentally, the transistor would not have survived if it had been possible to solder all three legs.  Why?  Because there was a short circuit between +5 volts and earth (ground) which is why the original transistor had blown.

I found and removed the shorted chips, made as good a job as I could of replacing the regulator transistor securely – quite hard when there’s nothing much left to solder to – thank you very much Mr Bodger.

I suppose the lesson here is – if using a repairer other than myself, for goodness sake make sure you use a good one!

How stupid of me … how would you know whether another repairer was any good?
Tricky one – I suppose you’d have to find out the hard way or come to me first.