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How to make a silk purse . . .

merrylander

merrylander

AK Member
out of not quite a sow's ear.

A while back I bought a yamaha PX-3 strictly as a parts unit. It was filthy, had no feet and was not guaranteed to do anything, the story begins;

This past Monday I swapped my good PX-3 for a PX-2 whose arm did not move. As it turned out, puting a new belt on the arm and replacing the right hand limit switch (high contact resistance) passed the 9-volt battery test

Put the arm back and the only thing it responded to was the manual left/right switches. Thinking it was the big 24 pin YM-294 chip I pulled the one from the PX-3 and put it in the PX-2, same problems, so I put back the original and buttoned up the PX-2 for another day.

So I put the YM-294 chip back in the PX-3 and while I had the board out, sprayed all the switch mechanisms with Deoxit. For laughs I plugged it in and all the functions except one work. It will only run at 45, but in order to save one button Yamaha decided to switch speeds in the PX-3 witha D-type flip flop. Figurin Mitt was not available I ordered several TC4013BP from B&D Enterprises, at least this part is still available.

Now this poor PX-3 was filthy and had no feet. Well soap and water does wonders and while I had some feet heavy enough to support her they were too short. Found some short bushings that lifted it up enough to suspend it just fine. The back of the dust cover was broken but I have some 4mm Plexiglass and plenty of acetone so perhaps that can be replaced.

So this was quite a restoration, well almost as there is still cleaning and dust cover repair, but it does show that well built components can be saved. It also proves - in my mind - that the PX-2s YM-294 chip is good since the one in the PX-3 is good and swapping them did not change the symptoms.
 
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Just finished using metal polish on the platter and Joy on the mat, then some Goof-Off to get the label remnants off the bottom plates, she's gonna be purdy
 
Nice find and a good job of fixing it up!

I love buying vintage turntables at yard sales. I've found some very nice turntables including a Yamaha P-20 in near-new condition.
 
Got the broken back off of the dust cover and a new piece of 4mm Plexiglass rough cut to make a new back. Now for the tedious task of filing it down. It won't be as pretty as a new cover, but hey - it's a dust cover intended to keep dust out.
 
There are a few marks here and there, but she runs like a new one. Was not the chip but a 100 ohm fusistor on the motor board - right in the line where the 33/45 signal is sent in.

Got the new back piece for the dust cover glued in, by no means perfect but it does what dustcovers do - keep out the dust.

All in all, considering this was the one that noone wanted to bid on - think the BIN was $90 - I am quite satisfied.
 
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Sucess with one seems to lead to the other, I have everything working on the PX-2 except for the 30cm, 25cm and 17cm lead in buttons, just a slow track-em down problem.
 
Great job on that TT Rob! :thmbsp: Just goes to show what a little patience, elbow grease and and ingenuity can accomplish! :thmbsp:
:ntwrthy: You da man!
 
Hang on to it long enough to compare to the PX-2 once you have it behaving the way you want. Will be interested in what you hear.
 
Congratulations. :thmbsp:
The comparison between the PX-2 and 3 should be as easy as a headshell/cartridge swap between the two arms.
Use a pack of cards(like feeler gauges)to determine that the arm height is the same.
Keep us informed. :yes:
 
Today I will have to see what output I get from the YM-294 chip in response to pressing any of the three buttons, proved the input was good, but the SM is not very helpfull.
 
Got the PX-2 sorted out, but had to canabalize the PX-3 to do it. Tried posting pictures in another thread but something is amiss with the server.
 
Glad you got the PX-2 going.
It's a shame that you had to take from the PX-3 though.
So what did you take from the PX-3 to the PX-2?

PS.
That's why I'm keeping my PX-3.It's the spare parts unit for my PX-2. :thmbsp:
I've had offers for it from Aussie AKers(and my spare 700C,C2x,M2A)
 
I took the three photodetectors that sense the arm position, Allen says they are NLA but I am looking through Mouser's catalog and think I have found some.
 
I'm not asking this question in a challenging manner:
I thought you'd gotten the PX-2 operational except for the 30 cM,25cM and 17cM selectors?
 
Exactly, what was happening was that with power on none of the record size buttons would start it up, no arm movement at all. However, if you used the manual buttons to move the arm off rest and start the platter then pressing either the 30 or 25 button would park the arm and stop the platter.

The whole procedure depends on those photo detectors not sending a signal until the arm reaches the set point, but they were all sending a high logic signal. Once I got the ones from the PX-3 in place on the PX-2 arm everything behaved as it should. Both arms have a metal bracket on the rear with 'flags' hanging down at measured points. When the flag interrupts the beam of the photo detector it signals the logic to stop the arm and set the cartridge down. If you remove the rear panel there are two screws that you can loosen and a cam you can turn that moves the whole detector assembly left or right so the stylus drops into the lead-in groove.

The good part is that I have found several photo detectors in the Mouser catalog so I should be able to put the PX-3 right.

Still don't know why the server will not upload pictures, I even deleted a bunch of old ones in case I was over the limit, but it still does not work.
 
I think AK's server is experiencing problems.
I've had trouble getting through to AK over the past day or so,and I see on other threads that people are having difficulty posting pictures.
Let's hope it sorts itself out. :yes:
I'm loath to dismantle my PXs.I don't want to jeopardise the 'tables(If it ain't broke....),so I appreciate this education you are giving us with your troubleshooting of these units.
Glad to hear that it was worth the effort.:thmbsp:
 
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