Vx Valvetronix VT15

[redneckgeek]

I have one of these on the bench. It has no output. I have a good signal through the pre amp board and into the main board (I call it the "main board", it's the bigger of the two with PS and Power transistor and tube on it).

I am trying to trace the signal. I have it on the input jack, the 12AX7 (6 and 1) one of the op amps (there are two) but no signal gets to the final audio power amplifier. It's difficult to trace a path because of all the toys incorporated into the amp.

I contacted Korg USA and asked politely for a schematic but, no dice. The docs are not available to the public yet.

I have tested all transistors, many resistors, all electrolytic caps. All test ok.

I was in hopes someone might have knowledge of this amp or even a source for a schematic for it. Thanks.

[Enzo]

Did you contact Vox directly?

[redneckgeek]

Vox Korg???

When I went on the Vox website I went to "contact us" and the result sent me to Korg USA. I don't remember the exact sequence of events. Suggestions?

[redneckgeek]

I have tested all of the transistors, tube, and the power transistor. I am unable find the op amps on mouser Newark or any other supplier. The op amp has on it: 0720 beneath that JRC and below that 9012B. I've tried to enter these markings in every way I can including separately to no avail. There is a JRC company - Japan Radio Company, but they manufacture marine radios, sonar and the like. Does ANY ONE HAVE ANY KNOWLEDGE OF THIS PART???

[Enzo]

JRC is like the Japanese version of what RCA was here. They make parts too. And as we mentioned in your other thread, this is a plain old VERY common TL072. 9012 means it was made in the 12th week of 1990.

The output IC is a TDA2050, and pin 1 is the input. Touch pin 1 with something like a little screwdriver or a paper clip bent straight. Careful not to touch pin 2 or anything else. Does sound come out then? If you hear a hum, then it is working, but if you get nothing, it may be bad. Pins 3 and 5 should have power for it. And is the speaker OK? And is there sound in the headphones? The headphones jack has a cutout contact on it that grounds the power amp mute. If that contact doesn;t work, then teh amp stays muted. One way to check that - on the phones jack pc board are there not two conectors - a three pin and a five pin? Check CN7-3 - that is the middle pin of the five pin. It should be grounded.