ONKYO TX-DS575

[PRR]

> Dave from EEVblog might be the one that first uttered the first commandment of electronics troubleshooting - "Thou shalt measure voltages"

That commandment is older than Dave's grandfather.

Still super-true.

 

[Khron]

... Hence my "disclaimer" My bad, but yes - amen to that (pun very much intended)

 

[saxmonster]

So with the Receiver plugged in and the power button disengagged I am getting 93.2VAC on the lead  to the power switch and the output lead of the switch reads 3.78VAC.  There should be nothing on that wire cause that is the wire that take the power back to the power pcb right?  Where is that 3.78vac coming from.  Is it a back feed from the big caps on the other pcb?

Engaging  the power switch the lead going to the switch now reads 92.4 and the return lead back to the power pcb now reads 92.4.

The yellow lead from the power pcb to the huge transformer reads 3.4vac  The white lead from the power pcb to the huge transformer reads    3.4vac.  Are these correct?


When I checked the output of JL961A(B)  The Power lead has no reading and the +13V lead has no reading and when I touch the earth lead to check for continuity between the chassie and the earth lead my DMM does not beep.

Getting 3.3vac between chassie and each side of the fuse.

ERRRRRRR

 

[Khron]

The "circuit ground" isn't directly tied to the chassis, from what i can see on the schematics. On page 21, in the mains input region, you'll see that the "ground" for the standby circuitry (the +13v that's currently absent) is connected to the chassis via C953.

Just for the hell of it, probe between the actual pins of JL961A (specifically between what should be +13v on the middle pin, and "ground", which should be pin 1 - i wouldn't be surprised if the wire to pin 1 had a different color too). This probing needs to be on the DC setting of your DMM, by the way.

Does your DMM has a diode test setting? If so, try testing D952 (with the leads both ways), it should be near that small transformer, on the AC input board.

Hint: lead colours tell us (who have no idea how the device looks on the inside) pretty much nothing, i'm afraid

On a side-note, 92VAC sounds a bit low, for 110V nominal mains (some 17% off).

 

[saxmonster]

So I probed between the  earth pin and the +13v pin and I get 21.1 VDC.  and Nothing between the power pin and the Earth pin.  Doesn't matter if the power switch is engaged or not.  Still reads 21.1vdc  These three pins are on a 3 wire ribbon type cable with the earth having a black strip running along the cable. 

I put my DMM in diode mode and one way it was OL and the other way it read .537  So I think it is ok, no?

So why is the mains so low where is it loosing those 18volts?

Again thanks for all your help

 

[Khron]

First of all, that's most definitely NOT "earth" - i've yet to see one of these AV-receivers that IS actually earthed (3-prong mains plug).

The "power" pin is the signal for closing the relay that routes the mains through the big main power transformer, so... if "even" stand-by doesn't work, "of course" there won't be any power (not to mention signal) for that.

The diode sounds ok, but 21V's a bit much, considering 1) it's supposed to be in the 12-13V range, and 2) the mains is actually almost 20% low. Also, the cap that's supposed to be filtering that is (on the schematic, at least) rated for 16v, so i'm a bit worried about that.

Either way, if THAT section kinda-sorta works, then your attention should be back to the power circuitry on the main PCB (as indicated in

Then there's a whole bunch of regulators and whatnot, on page 24, mid-right (where the 3-pin cable from the above circuitry comes in, via connector JL961A). You should be getting something around 5.6v at the output of Q931. That seems to go through connector P7001 to the front pcb, where the Micom is.

Is yours the model with the switchable 120/220v mains input? And no offense intended, but just how much DO you understand from schematics? Not trying to be condescending, just trying to figure out the level i should be describing things.

 

[saxmonster]

Then there's a whole bunch of regulators and whatnot, on page 24, mid-right (where the 3-pin cable from the above circuitry comes in, via connector JL961A). You should be getting something around 5.6v at the output of Q931. That seems to go through connector P7001 to the front pcb, where the Micom is.

I will try to get a reading from q931 in a bit.


Is yours the model with the switchable 120/220v mains input?

No there is no switch for that, I though that first maybe I did that when I as moving it.

And no offense intended, but just how much DO you understand from schematics? Not trying to be condescending, just trying to figure out the level i should be describing things.

[/quote]

no worries, i kinda understand it but hate following it from one section to another that's how I get lost. I like seeing it visually on a pcb.  But I know that's not how it works.  I am a music teacher by trade but have always taken stuff apart I have built chungers c12 mic.  I couple of others like a u87 type and also 500 series stuff like a sb4000,  La3a, and also a full DLA2A  from here.  I can following directions really good but don't necessarily understand why aand what a component exactly does in a circuit.

 

[Khron]

Well, in this case, it's not even THAT big of a deal, since all connectors and wires/signals are quite clearly (and even explicitly) labeled

 

[saxmonster]

Ok so the output of Q931  is reading  2.17VDC  So its not even half for the 5.6vdc needed.  I used the chassis for the ground / earth what ever it is yea there is no ground wire on the plug just a standard two pronged, stupid.  So does this mean that something has gone wrong on the power pcb?

Again thanks for you help.

 

[Khron]

That measurement was with the black probe on the chassis? That's not necessarily circuit ground.

Try probing again, if possible, on the legs of C935 (should be next to Q931).

 

[saxmonster]

Still got the same 2.17vdc using the negative side of Cap 935 for the black.

 

[Khron]

With that 21v on the input to Q931? That's quite odd indeed.

With the device unplugged from the mains, what's the resistance reading across C935? You could also try with the diode mode (both ways again).

 

[saxmonster]

I will try to get these readings tonight,  We were hit with a blizzard and lost power and all that fun stuff.  What controls the output of the power pcb.  It is so pose to be sending 13VDC right and its up to 21vdc.  Maybe it sees it as being too high and is doing something safe?  The thing is the power pcb is at the rear of the unit no where near the front panel where I replaced the parts.

Thanks again.

 

[saxmonster]

So with with the DMM in diode test mode and with black on the negative side the DMM reads .704 and when I switch them I get .602.

In ohms mode with black on neg it says 2261 and reversed it says 2280. 

Is this good or bad.

 

[Khron]

I don't suppose you have an oscilloscope handy, do you?

Regardless, considering you're getting 21v where normally you'd have 13v or so, i'm starting to seriously doubt the health of C952 (on the mains input board), since it was rated for 16v. I wonder what result replacing that one might have.

If that one's quite dead, or at least it's lost a lot of capacity, instead of DC at the input of that regulator there's only going to be some half-rectified AC, and that's not quite well. That would sort of explain the low output it has, since i have certain doubts the regulator itself has failed.

 

[saxmonster]

No oscilloscope handy sorry.  What would I be using that on? 

For c952 I can see if I have  one laying around the same 330uf 16v.

How do you think it went bad?  I always touch the case first to discharge static electricity.  I will try to replace it.

 

[saxmonster]

Well no luck with having that same size cap or anything close.  Will have to see if radio shack might have one or order one from digikey.

 

[Khron]

Well, the scope would've helped to see if / how much ripple is at the input of that voltage regulator.

At least the same capacitance (330u, 390u, 470u, 560u etc) and at least 25v (oe 35v or 50v) rating should be fine, as long as it can physically fit where the original one was.

Caps aren't affected by static electricity (as far as i know). But if it's rated for SIXTEEN volts, and since not long ago it has TWENTYONE on it... At least where i come from, 21 > 16, and when you apply more voltage than a part's rated for... that's usually bad

Aaaaand i'm pretty sure its age hasn't helped things either - electrolytics DO have a finite (shelf-)life, especially under load. The half-wave rectification "only" means more strain on that cap (their ripple current rating falls as the frequency gets lower).

 

[saxmonster]

Could it have gone bad from moving the unit around while working on it and storing it on the dinning table as I waited for part.  So fustrating how I wanted to fix one thing and another thing breaks.  So stupid.

Anyways I am going to place and order at digikey for C952 I will try to get 330 / 25v and a 35v one as there is a lot of room around it.  I will have to read up on the other capacitance and why they would also work.  Still have a lot to learn.

Are there any another parts you think I should order for questionable parts.  Should I rebuild the whole power pcb, hahhahah.

 

[Khron]

Well, at least for now, those would be the most obvious(?) culprits for why that 5.6v rail that supplies the main processor, isn't what it should be.

I quite doubt that 78M56 regulator crapped out, but... Ah hell, might as well order a 7805 (regardless of manufacturer), some plain ol' diode (from the 1N400x series should do) and a TO-220 silpad (or maybe a "kit" that comes with an insulating washer as well).