I recently picked up an onkyo ht-r667 to try to repair. It powers on but turns back off right when the relays click with a blinking standby light (i assume thats protection mode.) at first i suspected a damaged dsp because it seems like caps were added to the dsp to fix the hdmi problems that is apparently common to these units. But i found a pair of shorted output transistors, so i have removed them. Can i power on the receiver without the transistors in place to see if it will go into protect? I want to be sure they are the cause before i try to locate a replacement. i also have plenty of MN2488 + MP1620 in my parts bin, could i drop those in as temporary replacements to see if it will power on? the originals are c5242 + a1962. Thanks for any help!
It looks like all the solder connections are good on this receiver. I found two shorted output transistors. Can i power it up without the output transistors or will that damage something? Thanks!
From a lot of others on this thread doing the same thing... I would say try it. With the shorts gone the power transformer can turn on the way it is suppose to.
my experience with Onkyo has been that if the outputs are shorted, so are the drivers, and possibly the VAS and it's current source. there will probably be a bunch of those little flameproof resistors burned open too..... some Onkyo receivers i've seen may have damage all the way back to the diff amps. DON'T use the sony transistors to replace the outputs, even for testing. those MN and MP transistors are darlingtons. they will not bias properly, and their huge junction capacitance may make the amp channel oscillate.
Thanks! i checked other small transistors that were close to the burned channel and none seem to be shorted. If i power on with no output transistors will that damage anything? I want to make sure that was the only cause of the protect mode ( the dsp may still be bad)
I looked over the schematics, and the blown channel is one of the surround channels, I plan to use the unit in stereo or 3 channel mode, can it function without that channel?
Yes, it will work provided you remove the faulty transistors. But then, you will have take care of any supervisory connection that detects fault.
In general, there will be a dc detection circuit that gets its input from the output of a power amp. This will be there for all the channels. Connecting the unused (without transistors) output to ground may be all that is needed. Will have to see the schematic to be sure.
Gajanan Phadte
In general, there will be a dc detection circuit that gets its input from the output of a power amp. This will be there for all the channels. Connecting the unused (without transistors) output to ground may be all that is needed. Will have to see the schematic to be sure.
Gajanan Phadte
Thanks! hopefully thats all there is too it, i do not plan on using surround channels. I have attached the schmatic for the damaged channel. Thanks.
if you connect a 1500 ohm/2W resistor between each B-E connection of the place where the output transistors go, it will close the feedback loop and you can test the channel that way. you can apply signal to the channel and get a waveform out.... but make sure you don't connect a load.....
Very helpful info, thanks! i do not have 2 watt resistors though, i have lots of 470ohm .25 watt resistors. ive put 12 of them in series parrallel to give me a 1.41kohm resistor at 3watts, is this value close enough? I put it across the two outermost legs of where the transistors went? and the waveforms i hopefully get out will be at the speaker terminals? Thanks, hopefully ill have it running soon!
Thanks for all your help guys! I reassembled with the resistors in place and it seems to work. There is even a signal output on the blown channel, so i assume the driving circuit is fine and i just need to replace the power transistors. The only issues are, volume level seems pretty low, especially on HDMI, although it can get pretty loud, i just have to turn it up alot. And the receiver turns off when i turn up the volume sharply, even if the input is silent. I will be ordering replacement transistors soon.
Ok guys, im back again. I finally got around to testing the receiver, before ordering new transistors, so i connected 2 front speakers and a center. After about an hour of very quiet tv watching, another one of the surround channels decided to blow for no apparent reason. I have given up hope on fully fixing the receiver, but id like to try having atleast the front channels work. What do i have to remove from the board to run the receiver without the blown channel? Ill remove the blown power transistors, but what else should i do so the receiver can work without them?
If power amps blow seemingly randomly, check idle current on ALL channels. The bias setting arrangement is not inherently failsafe (by which I mean that contact issues in the pot would increase bias). Is one of the transistors in the bias circuitry mounted on the heatsink?
That was gonna be my next course of action to clean and reset all the biases. But first i have to find the simplest way to make the receiver work without those transistors in place? I have a feeling that other stuff will blow if i turn it on without the transistors in place
I have decided to continue working on this amplifier over my holiday break, so far i have reset the idle currents on all of the non blown channels (they all are in spec now) I tested the output signal of the blown channels with resistors substituted for the blown power transistors and there is a clean audio signal present on the speaker terminals of the blown channels (so that means the drive circuitry is fine?). I just installed new power transistors, but the amp draws excess current upon power up, it shuts down after 2secs. The idle current on the channels i replaced goes up to 1.6volts. I checked the adjust pots, and they are not the issue. What other components do i need to check next? thanks for any help! and forgive my ignorance, im still trying to learn.
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