PX-2 turntable hickups

[Dr. Ear]

Got a second PX-2 last week, mainly as a spare part donor. The cabinet is in a very good shape, so I am thinking of repairing the TT. The problem: The auto-mode does not work. Hitting the "30" button illuminates the corresponding LED only (no arm movement), the "17" button lowers the tonearm and the "25" button does nothing.
There are no open solder joints and all the components look fine. The manual mode (left, right, down, & up) works.

 

[rottalpha]

Got a second PX-2 last week, mainly as a spare part donor. The cabinet is in a very good shape, so I am thinking of repairing the TT. The problem: The auto-mode does not work. Hitting the "30" button illuminates the corresponding LED only (no arm movement), the "17" button lowers the tonearm and the "25" button does nothing.
There are no open solder joints and all the components look fine. The manual mode (left, right, down, & up) works.

I would suspect the contacts of those switches before anything else. Never worked on one so this is only a guess.

 

[Dr. Ear]

Switches are perfectly working.

 

[clinic-audio]

Hello Dr Ear

I have made many PX2 and work actually on PX 1

PM sent

 

[rottalpha]

and work actually on PX 1

how do you service that PX-1 without a service manual?

 

[Dr. Ear]

Today I transplanted the tonearm unit from my perfectly working PX-2 to the defective one. It showed the same erratic behavior in auto-modes as before. So it's definitely NOT the photointerrupters.
I have again looked carefully for bad solder joints, refluxed some, but it did not cure the problem. In manual mode the TT works fine.

 

[clinic-audio]

Do you mean that you put a "working" tone arm in a bad PX 2 ?
If something is dammaged on your bad tone arm , now it is the same with your "ex working tone arm " !
So it's definitely NOT the photointerrupters you can say that only if you place your " working" tone arm back in your working PX2 and everything go back to normal functions !
I hope you did not dammage anything in your working one !beause if it is the case , you have now two bad tone arms .....

 

[Dr. Ear]

I have put it already back in the healthy PX-2 and it works like before.

 

[clinic-audio]

Good news ! lucky man you are

 

[Dr. Ear]

So where to look now?

 

[Dr. Ear]

As the symptoms are exactly the same as with defective photo interrupters something in the circuit (outside the tonearm unit) is producing the same error.

 

[Dr. Ear]

Just tested: If I illuminate the photo interrupters with a strong light, the tonearm starts moving. But, the tonearm from my other healthy PX-2 does not work here either. There must be something in the circuit that prevents the IC YM294 from triggering. Not much in between the photo transistors and the IC

 

[rottalpha]

Just tested: If I illuminate the photo interrupters with a strong light, the tonearm starts moving. But, the tonearm from my other healthy PX-2 does not work here either. There must be something in the circuit that prevents the IC YM294 from triggering. Not much in between the photo transistors and the IC

there should be a source of light that hits the photo diode. If that source it is a simple light bulb, see if it is still working and replace if it is not working.

 

[Dr. Ear]

All 3 are working.

 

[Dr. Ear]

Will check all the voltages, maybe I find something.

 

[Dr. Ear]

Fixed. Found nothing suspicious in the arm control circuit. Did some surgery on the photo interrupters, which was the transplantation of new LED's. The first set I have tried was way too bright, causing malfunction of the auto return feature due to stray light. The other set was normal 3 mm 600 mcd red LED's. All the automatic functions are back to normal. I still do not have any explanation why the tonearm from my other, healthy PX-2 did not work here. Maybe some tired VD1212 or whatever. It is very important to keep the interrupters slim, i.e. bend the legs of the diodes immediately at the exit point from the plastic body, otherwise they will interfere with the shutters and potentially cause shorts. I used some black electric tape to prevent any shorts and to block stray light from the back of the unit.

 

[Dr. Ear]

I have tried 5 different photo interrupters from Digi-Key and Mouser which did not work. Either they are too tall (10 mm) or their pin layout does not fit.

 

[rottalpha]

The other set was normal 3 mm 600 mcd red LED's. All the automatic functions are back to normal.

the photo intrerupters seemed the main culprit based on your prior description. I am glad you did not give up. congrats!

 

[pfcs49]

somewhere here there's a thread on that and the guy only replaced the LEDs. I think he was from S Africa. I'll guess Shonover?- but he may be a recent PX2 player from Beo Forum. Was at least 5 years ago I think.

I have 3 new NOS interrupters and am considering selling two tables with one spare interrupter each, but expect you'd really need a set for full restoration?
If one of my PX2s got the syndrome, I'd definitely try 3 new LEDs nested in the old parts.
Good to hear your success. When the 2nd arm assy didn't work, my mind gave up
There's no motivation like when it's your own (valuable) piece!

 

[Dr. Ear]

Yes, I stumbled over this thread. This guy used 5mm LED‘s which are not suitable. He got problems with shorts and the auto stop feature did not work. Clinic Audio from France offered me NOS interrupters at a reasonable price, but he is quiet since then. So I had to find another solution.