Kenwood VR-505 Receiver No Audio, Loud Popping

[Robb]

I have a Kenwood VR-505 AV Receiver that powers on with display. It allows me to navigate the menu but I can't get any sound to come through and when changing the volume or switching input it makes a horrible popping or cracking noise. Does this sound familiar to anyone?

Service Manual -

[particleman]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

I would try cleaning pots with deoxit.

[rievax_60]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

Always a good idea to check all of the rails.

[Robb]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

I would try cleaning pots with deoxit.

Good idea, been meaning to get some anyway.

Always a good idea to check all the rails

Also a good idea but not sure where to check the voltages.

[particleman]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

You will have to d/l that service manual and it should show you voltage check points. Also those IC transistors (they may say darlington powerpack) that are screwed to the heatsink. A lot of the time those are bad you will need a volt meter. You will have to look up the type of module like stk-0050 or what ever. I have a kenwood ka-92b that had only one channel and needed the IC transistor replaced. I Also have a JVC that used stk-0050 darlington powerpacks and they both needed to be replaced. Once you figure out the module type you will be able to check resistance between the pins to find out if the module is bad.

[Robb]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

Thanks for helping me with this.

I d/l´d the SM but it's mostly just schematics which of coarse is good for someone who can read it still trying but it's slow going.

I checked the volts in/out of transformer
In: 120V, 1.2V
Out: -22V, -22V, 16V, .005V, 16V, 50V, 31V,.003V, 31V, 4V, 4V
Seems like some are low but it could be normal. I noticed some caps were rated at 75V and I'm not seeing any that high....

Those STKs seem a likely culprit as absolutely no sound emit except the popping and they're cold while other FETs/ICs seem to pass diode tests and get warm. But then again maybe they're not getting powered....
I will look into testing them.

Edit: I have an Oscope and ESR meter

[Robb]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

Apologies for double/triple posting but I'm having a hard time finding datasheets on these...anyone know a good source for datasheets?
STKs:
STK413-020A STK412-020A

[particleman]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

Just because the caps are 75V rated does not mean they will ever see that. The S/M should show you what the output from the power supply should be.

[Agent24]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

anyone know a good source for datasheets?
STKs:
STK413-020A STK412-020A

Sometimes it helps to search the main IC number eg STK412 without the suffix as some ICs in a family will have the same datasheet.

Thanks for helping me with this.

I d/l´d the SM but it's mostly just schematics which of coarse is good for someone who can read it still trying but it's slow going.

A schematic is easy to read. It's nothing more than a diagram showing component symbols and the connections (lines) between them.

For something like your amplifier there are many connections so there are many lines. One thing to note is that to avoid even more lines (and because there are multiple pages) not all lines will be drawn.

Some lines will be given a name (like Ground) and all lines with that same name are actually connected together, even if it's not shown directly.

I checked the volts in/out of transformer
In: 120V, 1.2V
Out: -22V, -22V, 16V, .005V, 16V, 50V, 31V,.003V, 31V, 4V, 4V
Seems like some are low but it could be normal. I noticed some caps were rated at 75V and I'm not seeing any that high....

Don't worry about the transformer too much. You want to check the output of the regulators etc. Page 13 of the schematic shows the transformer at bottom right and there are 3 diode bridges D1, D2 and D3 to the left of it. Also note regulators IC5 and IC6.

Each of these shows labels with voltages, You should check at those points for correct voltage to start with.

If the voltages are correct, make sure they are actually getting to the ICs.

The board layout on Page 10 shows where these components are physically on the board.

Those STKs seem a likely culprit as absolutely no sound emit except the popping and they're cold while other FETs/ICs seem to pass diode tests and get warm. But then again maybe they're not getting powered....
I will look into testing them.

Edit: I have an Oscope and ESR meter

Possibly they are bad, though it seems odd that both would fail at the same time. That would point to something else causing them to both not work.

They may have bad solder joints. There may be a problem with circuitry that affects both of them, eg: preamp, muting circuit etc.

A scope would be good for audio signal tracing. ESR meter probably not so much in an amplifier.

[Robb]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

Wow, thanx for all the practical info

Don't worry about the transformer too much. You want to check the output of the regulators etc. Page 13 of the schematic shows the transformer at bottom right and there are 3 diode bridges D1, D2 and D3 to the left of it. Also note regulators IC5 and IC6.

Each of these shows labels with voltages, You should check at those points for correct voltage to start with.

D1, D2, D3 all had correct voltages
IC5, IC6 should have had +20V/+12V & -20V/-12V respectively, however, all I could get was +20V from IC5 & -12V from IC6 the other two legs on each IC had .00xV. I found the ICs for $6/...ya think that's it?

[Agent24]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

You should get 20v on the input of IC5 and 12v on its output. Similarly, -21v on input of IC6 and -12v on the output.

Measure with respect to ground - put your meter negative lead on ground, probe the other two pins.

Note on Page 10 how IC5 and IC6 don't have the same pinouts for input, output and ground.

[Robb]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

I can't tell you how much I appreciate your putting the schematic into perspective for me...makes alot more sense to me now.

On IC5 I got +20V, .003V, .005V & on IC6 I got -12V, .003V, .005V. It looks to me like IC5 & IC6 need replaced.

UTSOURCE has the ICs for $2/each + $4 shipping so I'm going to replace em & hope for the best, unless otherwise advised.

[Agent24]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

No worries, glad I helped

Those readings are a bit odd, if you say the voltages from all the diode bridges are correct. Are you getting the +/-20v rails from the D3 bridge rectifier that feeds IC5 and IC6?

Are getting the +20v and -12v at the inputs to the regulators or the outputs? I assume at the inputs if your outputs are only millivolts. Did you check D3 and the regulators for dry solder joints?

In any case, new regulators are cheap but not sure I would buy them from eBay, especially China. If you can get them from Digikey\Mouser even RS etc that would be better.

[Robb]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

I was checking the voltages from the legs of the components. The diodes had four legs each. The outer two legs produced significant voltages - which were correct. The inner two legs did not.

As for the ICs, I think I should have measured a current on all three legs of each of the ICs, but I could only find volts on one of each.

I don't think there much between the Trans/diodes/ICs so, if I am measuring from the right spot, I'd guess it's the ICs...can't think of anything else at least.

[Agent24]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

The diodes (actually diode bridges as they have 4 diodes in each) take AC in on the inner pins (those marked with a ~) and rectify it to produce DC on the other pins marked + and -

If you are in DC volts mode when you measure the bridge input it will show nothing because there's actually AC there.


The regulator ICs should have an input voltage and an output voltage - and nothing on the third pin because it's ground.

I don't know how you checked before but the correct way would be this: If you look at the board overlay you will see how IC5 and IC6 have their leads labelled with G, I and O. G is Ground, I is Input and O is Output. Note also that the pin functions are not the same on each regulator.

Take the negative probe of your voltmeter and put it on the Ground\G pin, and then test the input and Output pins. Do the same for the other IC.

[Robb]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

Take the negative probe of your voltmeter and put it on the Ground\G pin, and then test the input and Output pins. Do the same for the other IC.

My previous voltage test was taken w/multimeter ground on a ground screw. I retested w/MM ground on the ground (middle) pins of IC5 & IC6 & got 20V/9V & -20V/-.5V where it should have read 20V/12V & -20V/-12V.
I also retested D1, D2 & D3 & got -66DC/50AC/50AC/66DC; -40DC/30AC/30AC/-40DC; -20DC/16AC/16AC/20DC respectively. The DC outputs were correct but I couldn't find a reference for the AC inputs.

Seems like IC5 should have 12V output instead of 9V & IC6 should have -12V instead of -.5V. Is it common for both to go out & is the 9V output within working range?

[Agent24]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

Seems like IC5 should have 12V output instead of 9V & IC6 should have -12V instead of -.5V. Is it common for both to go out & is the 9V output within working range?

I don't know about common failures on those regulators but yes, those voltages are wrong. 9v is not correct for a 12v regulator. It should be 12v.

Since the input voltages are OK, Either the regulator is bad, or something is shorted and loading it down, or the filter capacitors for it are bad.

You might as well replace the regulators anyway, but there may be other problems too.

[Robb]

Re: Kenwood VR-505 Receiver No Audio, Loud Popping

Ok, I'm going to go ahead & order the regulator ICs. Thanx for clearing things up for me.

I'll post the outcome of the replacements. Cheers