JVC RX-552VBK, no output from speakers or headphones.

[johnboy1313]

Let me preface this by admitting that I'm a tinkerer and sometimes, I screw things up because I don't know exactly what I'm doing.

I've been working on retrofitting the insides of this receiver into a wooden console shell that I bought at a thrift store. I only wanted two inputs, phono for the record player and video for the Bluetooth. I desoldered the variable resistor that controls the volume and added a couple feet of wire in order to be able to mount the pot into the appropriate hole in the console shell. At this point, the receiver still worked. I didn't want to have modern looking controls so I soldered a lead with a three position toggle switch to the backside of the control board in order to be able to switch inputs. I was successfully able to switch inputs by switching the toggle on (up for phono) then off, or on (down for video) then off. At this point the receiver still worked. I wanted to be able to power on and switch inputs with one knob so I put a 2 pole 6 position rotary switch in place of the toggle.

Pole 1:
Pin 1 - Video
Pin 2 - None
Pin 3 - None
Pin 4 - None
Pin 5 - Phono
Pin 6 - None

Pole:2
Pin 1 - None
Pin 2 - On/Off
Pin 3 - None
Pin 4 - On/Off
Pin 5 - None
Pin 6 - None

The theory was that the switch would be set to Position 3 in standby. Switching to position 2 or 4 would power the unit on, then switching to position 1 or 5 would select the source. To switch from one source to the other, you would power off, then back on, then select the other source.

So, here's where I screwed up. I soldered both the video and the phono wires to the opposite pins of the power wire without looking it over to see that I made a mistake. It was as if I was trying to select the source and power on at the same time. I didn't have a speaker connected so I'm not sure exactly when things went askew. When I powered the unit on, all seemed fine, when I switched to the first source, the display changed as it should. When I switched to the other source, the display again changed, but there was a pop. This is the point that I believed I damaged it. I looked over my wiring and corrected my mistake. Since I didn't have a speaker connected and because the display changed like it was supposed to, I thought I got away with something. The unit still seemed like it was working so I proceeded to add extensions to the Bass and Treble pots as well. I desoldered them and added two feet of wire between the board and the pot. This is when I connected everything back together with a speaker and realized there was no output from any source including the radio. I plugged in headphones and there is no sound there either.

Per the attached power schematic, all DC voltages are present except it looks like I've lost the 4.8V rail, it measures millivolts at all points across the board. I'm going to try to trace that rail.

Also, I notice there are AC voltages shown on the schematic. How to I measure the AC voltages? What do I put the black lead on? One of the legs of the main cap?

[DJduck]

Re: JVC RX-552VBK, no output from speakers or headphones.

To measure the AC voltages, there should be two AC wires, just measure between them. If there is only one "active" AC wire, measure between the wire and ground. At least that is how it should be, me thinks.

As for the 4.8V rail, It should either use a regulator or a transistor or something to regulate it, or perhaps a zener. Find the component that controls the rail and check it. If it's a regulator, measure input and output. If there is input but no output, that regulator is toasted. If no input, you have to trace even further to find what what gives it input voltage. Also check any resistors and caps on the 4.8V rail to make sure none of the fried along with the regulator.

I can't look at the schematic right now, but if this thing uses an input selector controller, you might have accidentally fried it, and if it's a special proprietary controller, you might not find a replacement.

Good luck with the repair!