Kenwood AVS Receiver KRF-V5300D in protect blinking LED

[tw2005]

Kenwood AVS Receiver KRF-5300D in protect with blinking LED. Would apply to other models like KRF-V5200D etc.

Unit would briefly power up and go protect, Standby LED rapid blinks.

Found both AVR & IC-PROT2 , & AMP DC-PROT1 active high

Checked -12V (7912 reg IC4) & +12v (7812 reg, IC3) missing voltage

Checked input side of both regs, missing -22.7V & +22.3V

Checked Transformer output at CN2 pin 1 12VAC & pin 3 -12VAC, both present

identified R527 , 528 1 ohm 0.25w flameproof resistors , discoloured, burnt , open cct.

Replaced resistors, At this point the receiver was effectively fixed but remained with the same fault symptoms. So this was my dumb moment I'll share.

voltages were restored but not in spec and unstable.
+12V was erratic and 11.2-11.5v
-12V was about -6V, replaced that 7912 and -12V but I'll get back to this.

unit still failed.

looking at the cct where the two protection circuits are, there was a checkpoint at zener cathode D305 3.3V and c303 + of 3.6v.
I had 10V and suspected bad zener, purchased a replacement but diode check indicated it was ok but swapped out anyway - no change

then proceeded to check all voltages and for anything shorted or open etc, could not find anything obvious

If connector cn601 is removed the unit will powerup since the protect signals are now isolated. Risky move but i could not find any shorted items especially the amp modules.
Nothing bad happened so connected cn601, earthed the protects and turned on, nothing bad, no smoke, hooked a speaker up and amp could be heard coming online through the speaker.

So I'm back at the 10V which should be 3.6 or less I suspect. If 10V is on the zener reversed it should be conducting and pulling that down

I've already checked that zener and swapped an axial 1/2w 3.3v so i'd run out of ideas. I thought I'd try it again but this time earthed to chassis and then on the + side on the cap. Voltage went from 10v to 2.5v

I think some of you know where this is heading.

Where did I go wrong? Nothing earthed correctly, floating gnds!

None of these boards earth with the mounting screws but via earth brackets screwed to the rear panel. none of these were bolted as i had removed all these.

Yeah, 2 nights poking and pondering the schematic with a dead end.

So what about the 7912 reg coming good, well i'm pretty sure I used the chassis gnd for the low reading and after replacement used the actual gnd at the reg so original was most likely good.

have not gone back to the original as I could not be stuffed now but once I realised what was going on, bolted all earth points up and working.

So short version, missing +- 12V rails , open cct resistors cut AC before the rectifiers.

I used the KRF-V5200d service manual as the boards are virtually the same, definitely the power board was.

Cheap, quick fix if you have better practices than I on this occasion

[budm]

Re: Kenwood AVS Receiver KRF-V5300D in protect blinking LED

Can you upload the service manual or give me the link for me to download?
Is this the one you are using?
http://elektrotanya.com/?q=showresul...at2=schematics
Are all the circuit board mounting screws are tight since the GND are tied to chassis via the board mounting screws?
Do do still get 10V on that Zener D305?

[SteveNielsen]

Re: Kenwood AVS Receiver KRF-V5300D in protect blinking LED

It may well have been just a bad ground connection. If you're real curious start removing chassis ground points for the board until the problem comes back.

[budm]

Re: Kenwood AVS Receiver KRF-V5300D in protect blinking LED

BTW, the Voltage feeding the 3.3V Zener D305 for running the protection detection circuits are fed from OR Diode D304 circuit via R320 (+11.9V), R321 (+9.8V).
You probably has bad GND if you use the chassis as the GND ref instead of measuring directly between the two legs of the Diode.

[budm]

Re: Kenwood AVS Receiver KRF-V5300D in protect blinking LED

So what DCV do you have at ''A', and 'B'?
BTW, the detection circuits have to be able to detect the Positive or Negative DC offset at the output of the power amps since the power amps use bipolar power supply.

[tw2005]

Re: Kenwood AVS Receiver KRF-V5300D in protect blinking LED

Hi BUDM and steve, as i mentioned this is fixed. Unfortunately i can't provide the info requested since I popped it in the car and took it to work to give back to the owner.

the original fault was 2 open resistors for +12V and -12V supply via the ac out of the transformer hence no + _ dc supply to the regulators.

no not all board screws were in but I did look at the underside and did not see any earth pads for the screws but maybe i'm worng, i took no photos eithersorry.

i do know though 100% that each board had a 90degree bracket that was soldered to earth and then all earthed together via the back panel which is steel.

Once I screwed those up i was in business. I then put the remaining pcb screws in.

Academic now but that's what happened. At the zener I saw 2.5v doing that extra zener across the other and earthing it. I did not go back to recheck where it was at with everything in place. i moved on happy with the fact it was fixed.

Never worked on audio before but it's always fun learning something along the way.
At least i was in the right place to work it out in the end

[budm]

Re: Kenwood AVS Receiver KRF-V5300D in protect blinking LED

OK, I thought you had to CN601 to make it work.
The only way I think you were getting 10V on the Zener was due to bad ground.
But I am glad you got it running. When I repair these units that depend on the screws for grounding the board I will solder the buss wires to the GND pad to the chassis so I do not have to worry about the corrosion between the GND pads and the chassis or if the screws become loose.

[tw2005]

Re: Kenwood AVS Receiver KRF-V5300D in protect blinking LED

OK, I thought you had to CN601 to make it work.
The only way I think you were getting 10V on the Zener was due to bad ground.
But I am glad you got it running. When I repair these units that depend on the screws for grounding the board I will solder the buss wires to the from the GND pad to the chassis so I do not have to worry about the corrosion between the GND pad and the chassis or the srews become loose.

Correct, disconnecting the ribbon at cn601 allowed the power board to remain on, but no main or display due to main board isolated. Forcing the 2 protect line to low/grounded with cn601 connected also gave full functionality.

I almost posted my problem up seeking help but gave it that bit more thought.

Try to work things out myself as far as i can, it's a pride thing but does show how easy you can do something not knowing and introduce a new problem which is how it turned out.

I hate quitting, was going to, glad i persisted, cheers

[tw2005]

Re: Kenwood AVS Receiver KRF-V5300D in protect blinking LED

Something else I should mention, I learnt today that it went out after lightning. something I forgot over time so probably explains why both resistors failed simultaneously which had me curious so unlikely this is a design flaw.