Harman Kardon AVR 146 Won't stay powered

[Bslodk]

I am a novice at this, but I am trying isolate a problem with my brother-in-law's Harmen Kardon AVR 146. I suspect a bad cap, but not sure where to start looking. I think it is going into Power Fail mode? I looked at the control boards I could visibly see and do not see anything standing out like a bulging cap or cracked solder connection.

I did do a full processor reboot and have all the speakers disconnected, but it still will not stay powered on, nor will the front screen show any signs of life.

The symptom:

With the system in standby mode, when source is selected the unit tries to power up and I hear a relay kick in and after about 3 - 4 seconds it goes back into standby mode. During the attempt to power up,
there is no sign of visible life on the front screen. I have the schematic, but not sure where to start tracing. Any help/assistance would be greatly appreciated.

I am a new member and read through the guidelines and posted a picture looking down and some of the schematics. Maybe one of the big caps on the main board? I am just not sure where to start tracing.

[Bslodk]

Re: Harmon Karden AVR 146 Won't stay powered

Anyone? I was hoping to start troubleshooting this weekend.

[dmill89]

Re: Harmon Karden AVR 146 Won't stay powered

It may just be the angle of the picture but it looks like some of the caps on the front power supply board (the one in front of the transformer)may be bulging. That transformer also looks like it got very hot (yellowing of the plastic and what appear to be dark marks on the blue plastic wrapping) there is a chance it may have tripped the thermal fuse inside of the transformer (will show as an open circuit).

If none-of those are the culprit it would probably be a good idea to test the power transistors (the ones on the big heatsink), since it is shutting down immediately on start up, one of those may be bad and tripping the protection circuit.

[R_J]

Re: Harmon Karden AVR 146 Won't stay powered

What you can do is with your meter on dc volts and black lead to chassis ground, check on one of the small pins of the white plug (by the large white resitors and nothing connected to them) (there are 5 one for each channel) with the amp turned on there should be less than 1 volt to ground, If you measure more than that, then that amp channel has a problem. you can then check the output transistors etc.
Between those two pins is where you adjust the bias for that amp section, but it is also the center of the output pair and should be close to zero volts, any large plus or minus voltage will trip the protection circuit.

I should also add these are a pain in the ass to work on, they rely on the tin chassis for grounding so if you remove a board to work on it, you need to reassemble it to try it. all I can say is be carefull and don't let the smoke escape.

That transformer has varnish on it, they always look yellowish.

[dmill89]

Re: Harmon Karden AVR 146 Won't stay powered

On a side note, while it would probably be beneficial to check the "simple" and "cheap" stuff I'd be hesitent to put too much money/time into an AVR 146, they were an "entry-level" model and you can find them for less than $50 on ebay. Though you could probably also find a better used reciever for $50-100 on ebay, especially if you don't need HDMI switching, non-HDMI recievers are selling for next to nothing these days with even high-end models routinely selling for less than $100.

[Bslodk]

Re: Harmon Karden AVR 146 Won't stay powered

Ok, guys I took R_J's advice and checked voltage at each of the channels (white plugs with nothing connected). All are below 1 volt. Some were as low as .02 while others were at .07 and .08 and climbing until it shutdown. I thought about mucking with the bias, but thought I better wait until one of you experts provide some additional guidance.

Is it of any importance that the front panel is not displaying any information whatsoever OR is this normal assuming the unit is going into power fail? Also, looking at the schematic I wanted to be sure I understand the difference between "P_line fail" on the block diagram and "protect". They are two different things, correct?

Also, I understand these are cheaper units, but I am looking more to learn about reading circuits and repairing. Any additional advice where to look next would be greatly appreciated.

[Agent24]

Re: Harmon Karden AVR 146 Won't stay powered

Have you checked that all the power supply rails are present and correct, and that any secondary regulators (there will likely be some for the digital control section) are outputting the right voltages? Also check they do not go out of spec when the system tries to power up.

[kc8adu]

Re: Harmon Karden AVR 146 Won't stay powered

iirc these have a standby independant of the main tranny.
the display,ect needs supplies from the main section.if it does not start and come ready within a certain time it shuts down.so while it up check that the main supplies come up.
the one i had was a thermal fuse in the main transformer.

[Bslodk]

Re: Harmon Karden AVR 146 Won't stay powered

I know I am showing my ignorance here, but where do I check for the main supply voltages? I am attaching the entire schematic, but I do not see anywhere on the schematic where it shows I can see the direct output voltages from the transformer. What I have primarily been looking at is page 170.

I do find all of the plugs and the boards. Looking at the connector on 11916-4 (9 pin connector) the nomenclature is confusing to me. pin 1 +5vd pin 2 17v, etc. what is +5VD? Does that mean +5 dc volts? and pin 8, 5.6VC. What is VC ?

On board 11916 I see the two rectifiers (I believe that is what they are), but once again no voltages on the schematic. I apologize for being so delusional and confused IN ADVANCED. HELP!

[Agent24]

Re: Harmon Karden AVR 146 Won't stay powered

The block diagram on page 38 might help you (centre right). Note you have two transformers. Standby one and main one.

Anyway the connector is labelled as you say, so you could measure the voltages there for a start.

The extra letters after the +5V are talking about certain rails for certain functions. So yes, +5VD would be +5v. You know it's DC because the diagram shows a regulator. According to page 38, +5VD is for the DSP. I can't see where it says what +5.6VC is for.

Anyway, it doesn't really matter, as long as the voltage is correct.

[Bslodk]

Re: Harmon Karden AVR 146 Won't stay powered

Thank you for the clarification. I start this weekend on tracing. I appreciate the guidance.

[Bslodk]

Re: Harmon Karden AVR 146 Won't stay powered

Guys,

I am beginning to suspect a bad transformer. I cannot tell what type of A/C voltage I should be getting out of the posts at the transformer, but all are less than 1VAC. There is a slight vibration coming from the transformer (like a bad connection of some sort internally), but not a hum. Additionally, when I check voltages for DC at the rectifiers on D991 and D992 I get nothing. Presently, the transformer is completely disconnected from the chassis with the exception of only the 120 VAC power supplying the transformer. I have verified I have 120VAC going to the transformer.

I cannot find anywhere in the specifications or schematic what kind of voltages I should be seeing at the transformer. Oddly enough, the user saw no smoke or anything like that when it quit on him. I see no powder burns, smell of smoke, etc. at the transformer either. Do you concur with my findings OR should I be disconnecting both circuit boards from the transformer to ensure there is not a short somewhere on one of the soldered boards that are attached to the transformer?

[stj]

Re: Harmon Karden AVR 146 Won't stay powered

that's a terrible design, it's just screaming for cracked solder joints.

[R_J]

Re: Harmon Karden AVR 146 Won't stay powered

With no ac connected, what is the resistance accross the primary (accross the ac plug)

[budm]

Re: Harmon Karden AVR 146 Won't stay powered

Check the transformer primary winding resistance on connector CN91 which is connected directly to the two wires of the primary winding, unit not plug in of course. The resistance will be very low <5 Ohms. You do have low resistance reading, then you can plug the unit into the outlet, hit the power button, then you should hear the relay RY94 kick on to supply 120VAC to CN91 pin 1 and 2.

[budm]

Re: Harmon Karden AVR 146 Won't stay powered

BTW, this unit uses the similar circuit as used here in the power supply section:
https://www.badcaps.net/forum/showth...=HARMAN+KARDON

Check all those ceramic caps and fusible resistors.

[budm]

Re: Harmon Karden AVR 146 Won't stay powered

Hi R_J, what did you use to unlock the PDF on post 9? Thanks.

[stj]

Re: Harmon Karden AVR 146 Won't stay powered

it's not locked,
i just opened it wih both okular and foxit

[budm]

Re: Harmon Karden AVR 146 Won't stay powered

Hmm, I use ACR9, as you can see in the post 16, the header shows (SECURED). I can open it but cannot do any modification such as page extraction.
I am able to do work around and able to extract the SCH pages.

[Bslodk]

Re: Harmon Karden AVR 146 Won't stay powered

Disconnecting the wires at CN91 and checking resistance on the wires to the transformer I get NOTHING! No resistance so I assume this means the transformer is indeed shot, right?

I did not check the resistors eariler and they checked out. I have not checked the caps in your highlighted diagram because at this point I am not getting resistance on the wires and secondly, I did not want to start unsoldering the caps if it looks like the transformer is indeed bad.

Do we agree that it looks like it is indeed the transformer?