Onkyo TX SV727: Found bad transistors, what else?

[rievax_60]

Re: Onkyo TX SV727: Found bad transistors, what else?

Does the amplifier stay on? You forgot to say what the offset voltage is. Does the heatsink get hot quickly?

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

The unit stays on, just in protect mode, no matter whats hooked up to it. No heat on transistors or heatsink. Will measure voltage on the emitter resistors tonight.

[Drack]

Re: Onkyo TX SV727: Found bad transistors, what else?

Hi guys one question, when you are using your amp is normal to have DC and AC voltages on the speaker terminals (10vdc and 18vac respectively if I remember correctly at 60/70% of capacity)

[rievax_60]

Re: Onkyo TX SV727: Found bad transistors, what else?

Hi guys one question, when you are using your amp is normal to have DC and AC voltages on the speaker terminals (10vdc and 18vac respectively if I remember correctly at 60/70% of capacity)

A fluctuating AC voltage would be normal if it is only the output audio signal that is being measured. A DC reading like that would not be normal and is capable of causing distortion and damaging speakers.
I'm possibly misunderstanding your message.

[petehall347]

Re: Onkyo TX SV727: Found bad transistors, what else?

10 vdc is serious clipping ..dont ever go there unless you are a pyromaniac with a strange sense of humour .

[Drack]

Re: Onkyo TX SV727: Found bad transistors, what else?

That's while playing some songs, there is almost no distortion at all, is a Technics su500, and it's working perfectly just wanted to know if that was normal

[budm]

Re: Onkyo TX SV727: Found bad transistors, what else?

I doubt that you actually have 10 VDC on the speaker Voice coil.
Must be measurement error, how did you set the meter to AC, DC at what scale, V, mV, etc.
Ni way you can have 10 and still working, that much DC the speaker cone will either be all the way in or all the way out. Is the test done without signal applied?
When the DATA is wrong you know something is not done right.

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Ok guys.
Took her to work where the guys here have good Fluke meters.

We got a problem!

So i measured all the resistor legs with respect to ground. Starting from the front of the stereo, to the back.

R1->GND = 0.016v
R2->GND = 0.01v (center leg)
R3->GND = 0.003v

Now where i did my repair:

R4-> GND = 49.01V (uh oh!)
R5->GND = 49.03V (center leg)
R6->GND = 49V

R7->GND = 0.008v
R8->GND = 0.02V
R9->GND = -0.005v

R10->GND = 0.008v
R11->GND = 0.003v
R12->GND = -0.003v

[Drack]

Re: Onkyo TX SV727: Found bad transistors, what else?

Budm i said it was while playing a song, and I checked again and had the same results, but everything is working fine so I now used my dad's DMM and the maximum DC while no signal applied on 200mv range was 7mv and while playing a song at low volume was 20mv.
So now I have good and bad news, my amp is ok(good) but my meter is not and it has a new battery so it's not that.
Sorry op for using your thread for my question

[rievax_60]

Re: Onkyo TX SV727: Found bad transistors, what else?

Ok guys.
Took her to work where the guys here have good Fluke meters.

We got a problem!

So i measured all the resistor legs with respect to ground. Starting from the front of the stereo, to the back.

R1->GND = 0.016v
R2->GND = 0.01v (center leg)
R3->GND = 0.003v

Now where i did my repair:

R4-> GND = 49.01V (uh oh!)
R5->GND = 49.03V (center leg)
R6->GND = 49V

R7->GND = 0.008v
R8->GND = 0.02V
R9->GND = -0.005v

R10->GND = 0.008v
R11->GND = 0.003v
R12->GND = -0.003v

If the symptom was intermittent, there should be no permanent damage. There could be a broken track somewhere between the Base of the PNP output transistor and the Voltage Amplifier stage.
Also check for C to E short on the NPN output transistor.

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

I'll do some digging and probing. I recall doing a continuity test right after this happened on all the big transistors and none showed shorts. I know the 2 i replaced arent shorted...first thing i checked lol.
I have the 2SD transistor on the left, and the 2SB15560 on the right. Any chance i switched em?

I'm printing off the schematics tomorrow at work. Preferably on the plotter for ease of reading.

If i screwed up a track/caused a short id guess itd be by where my soldering was. I'm just still puzzled why this was "working" until i hooked my meter to the outputs. Unless my junk meter showed up as a short?

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Well i screwed up royally. Not even sure how!!
I checked all my transistors. No shorts. Checked my new resistor, it was making continuity.

The one thing i did do was clean up the crud and grime around my solder joints.

Apparently. I screwed something up doing that because when i powered it on: POP!

Fuse is gone. Also, more troubling, i dont have standby it seems! Before when the transistors were shorted itd blow the fuse, but id still have standby.

Even worse, both of my replaced transistors are now shorted. Different pins it seems this time.

So i guess im back to step 1. Remove the shorted transistors and replace with 1k resistors to see if she turns on.

Im half tempted to take it to a repair place, but now it's personal!

[rievax_60]

Re: Onkyo TX SV727: Found bad transistors, what else?

Considering that there was no load on the output, the only other cause for what happened is a fault in the idle current setting circuit. Likely a cracked track or a poor solder joint.
Even faults that cause large DC offsets will not necessarily blow the output stage unless the output is purposely shorted to ground.

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Reivax so i understand better, the 2 transistors i replaced, is that the output stage? I thought it was the 2 bigger transistors next to it

[rievax_60]

Re: Onkyo TX SV727: Found bad transistors, what else?

Earlier you said, "The old 2SB1558 and 2SD2387? yes. Both showed shorts from B to E in both directions both in and out of circuit." Are these the transistors that have just failed again? These are large transistors. Im not certain what the 2 biggers ones are. I have not seen them.
"Output Stage" usually refers to the large transistors and other components in the final stage of the amplifier that outputs the amplified signal to the speakers.

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Yes these are the same 2 that shorted.

Ok, yeah i was referring to the "bigger" ones as the "last" ones before the output stage.

When i plug it in now even with the blown fuse i hear a relay click on, which i dont remember getting before...