Adjusting Sony PS-X70 with scope

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According to the service manual when adjusting RV2 and RV3 to set resp. 45rpm and 33rpm a waveform similar to the reference waveform should appear (scope connected to the two pins of the block as in diagram). I get a completely different waveform than the block waveform and nothing changes when adjusting the pots.

Could it be that I need to setup the scope differently or perhaps there is another explanation?

The power supply voltages seem ok (negative voltage is -35v instead of -34v). Two diodes, VD1221, have been replaced as they sometimes cause problems. The turntable had a full recap and all joints have been resoldered.

What's the next logical step? Checking all voltages, checking transistors or something else?

Your help, as always, is much appreciated!
 

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I have 2 PS X70 TTs. The 45rpm function of the second one doesn't work properly. If you hold the key it goes to 45rpm, but the LED light doesn't come on (doesn't lock). And when first powered up the auto start function puts the needle in the wrong spot (after that it's fine). The TT does smell a bit when powered up. :) Not the most easy to fix TTs. :)
 
Started measuring all the voltage on the power supply, as indicated in the service manual, and one of the transistors was dead (Q501). Got a replacement transistor and the auto-return function works again! All the diodes in PS seem to test ok, but the voltage on one of the legs of Q401 and Q406 don't measure the indicated resp. 34V and 35V. Should I further investigate this? All the other voltages of the power supply are spot on.

When checking the waveform of the 33/45 rpm I still get a different waveform (noise) than the block waveform. Any idea what could be the problem? (apart from me not being a skilled technician ;) )
 
Can anyone explain how to connect the power supply and probe to calibrate the Hall Device Gain Adjustment and Motor Amp Offset Adjustment? Where should the power supply ground be connected to and the 1.5VDC? (I don't understand the ground symbol in combination with _ symbol at the top)

I have disconnected the white wire as indicated in the service manual.

Also, what about the ground for the probe? Should it share the same ground point as the power supply?

Hope someone can help me out here. :)
 
I forgot to include the page of the service manual which explains how to connect the external power supply (1.5VDC) and scope probes. With my limited understanding I don't understand how to connect the power supply exactly. :(
 

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Found out that the turntable needs to be powered on to adjust the motor offset with the lab power supply connected (1.5V) as well. Was able to adjust it by dealing the voltage to 0 connecting my VOM.

I still can't figure out how to connect the scope when adjusting both the Hall Device Gain and Motor Amp Offset. Hmmm... will have to study the Rigol manual a bit more ;)
 
Ok, hopefully someone can check me on this.



I have the regulated 1.5V DC power and scope set up this way:


Power + to the middle pin as shown in the service manual (this is labeled 37 on the component side of the board)
Power ground to chassis.


Scope probe to H1 to adjust RV4. What's shown in the service manual photo doesn't agree with the schematic. The latter shows H1 to be the pin with a solid red and white wire, coming from the group of five pins/wires right behind the adjustment pots. This pin/wire is labeled 57 on the board.


Scope ground to chassis.



While I believe these are the correct connections, I'm not getting anything on the scope. Checking voltages with my meter, I see 1.5V DC at the base of the pin where the lead from the power supply is connected. Then it drops to 1.2V after R63 (220 ohm). Then it comes to one of RV6 and RV4 as 1.2V, but then is nearly zero on the other side, after two resistors (R47 and R48) where H2 and H1 would be used for the measurements. So it makes sense that I'm not seeing anything on the scope (there's no voltage) but why?



#freebee. If you'd prefer I move this to a different thread, I will, but I thought it was relevant to your discussion,
 
One of the things I concluded from an other Sony service manual (different DD turntable) is that the turntable needs to be plugged in and switched on to get the waveform. which is counter-intuitive as you are feeding it 1.5vdc as well.

My problem is that the waveform isn't steady and not like the one described in the service manual. At first I thought it to be a defective part, but I have 2 Sony PS-X70 turntables which show exactly the same. Maybe it's my inexperience with a scope and I need to change the settings on my Rigol DS1054Z.
 
I noticed that the old solder flux attracts a lot of dirt and I had to clean the PCB with alcohol and a toothbrush to get rid of it all. This actually solved a speed problem with one of the turntables.

Can you do me a favor? I'd like to see the waveforms you get at pin 1 of IC1 with power on only, then with the Start button pressed, and lastly with a record playing. This would be helpful to me in my attempt to diagnose the motor issue I'm trying to diagnose.
 
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