Vestax clone

[allachikatillo]

Hi!

I'm trying to clone vestax from original circuit for study project. Made the PCBs, but it doesn't work properly. The volume is low, pots doesn't much effect the sound (completely turned down pots still sending signal) and phones doesn't work as well.

I've checked the pcb and everything is connected right. But I find out the problem with transistor 2sc1627, it is to weak to supply U19 and phones pcb part.
Shorting the C and E out makes U19 working, but U7 distort the sound in phones.

The solving this problem doesn't mean the solving problem of the whole circuit. The question is why the original circuit doesn't work as it should be. Changing the transistor or supply part doesn't solve the problem with pots (i use this https://lib.chipdip.ru/995/DOC000995779.pdf, every pot is well grounded). I think something is causing all this problems, but can't find it.

I surmise thats its all about GND or supply in general.

What should I check or re-check, to find the problem?

 

[Les Jones]

The fact that the phone output is distorted would suggest that the fault is in that part of the circuit causing it to draw too much current. Possibly U7 is faulty or an electrolytic capacitor in that part of the circuit is inserted with it's polarity wrong and changing the DC conditions on U7. I would see if the voltage "VM" comes up to the correct level if you unplug connector H7C (Or remove U7 if it is in a socket.) The problem with the pots not working as expected could be due to the way the ground connections are done. (NOTE there are two different symbols used for ground.) The two parts of the ground path are only connected at one point - H2C / CN2J connector. Check that the two ground paths are connected. If this is not the cause then just use normal fault finding methods by tracing the signal from a signal generator through the circuit with an oscilloscope.

Les.

 

[allachikatillo]

The fact that the phone output is distorted would suggest that the fault is in that part of the circuit causing it to draw too much current. Possibly U7 is faulty or an electrolytic capacitor in that part of the circuit is inserted with it's polarity wrong and changing the DC conditions on U7. I would see if the voltage "VM" comes up to the correct level if you unplug connector H7C (Or remove U7 if it is in a socket.) The problem with the pots not working as expected could be due to the way the ground connections are done. (NOTE there are two different symbols used for ground.) The two parts of the ground path are only connected at one point - H2C / CN2J connector. Check that the two ground paths are connected. If this is not the cause then just use normal fault finding methods by tracing the signal from a signal generator through the circuit with an oscilloscope.

Les.

I see. Removing H7C connection, totally removing U7 from the socket or that transistor do nothing. Capacitor polarity is right.
And, by the way, H4C connection provide right voltage. And ground is connected.
I have to pcbs with and two grounds are only connected at H2C / CN2J. The same for the GND & GND1 - the Single Point grounding for GND and ground plane GND1 .
I would like to use an oscilloscope to trace the signals but I don't have it now

UPD: Strange thing happen - if i totally disconnect GND2 point on H2C/CN2J the LED11 (Power Led) is still working (while the pwr is on). How it can be explained, there is no any GND connection on this board.