I tested the output transistors on that channel and they’re still testing good on my transistor meter. Should I still worry about them?
Dan
My fault or fault of the dog?
- Thread starter saabracer23
- Start date
I tested the output transistors on that channel and they’re still testing good on my transistor meter. Should I still worry about them?
Dan
UncleBingo
Super Member
What is the rail voltage on those output transistors?
ETLS
metacarpophalangealcranium
Wow, good thing you saw the wire damage. Not your fault the dog chewed the wiring. Glad he didn't try to hide the damage, and try to shift the blame for a free repair.
shelly_d
Not An Audiophool
With that much voltage on the output my first guess would be a output as well. If indeed the output transistors are good, you may have a fault that is driving one of them to full on at saturation. I would check the driver transistors Q413 and 415 on the posted schematic. Get the EBC voltages and check them against the manual. Then pull them and check them on your transistor checker. If the transistors check good, there may be a fault that is driving one of them into saturation.
Warning: This is somewhat guesswork on my part but if you don't have any better suggestions, this may be worth a shot.
Good Luck
Shelly_D
Warning: This is somewhat guesswork on my part but if you don't have any better suggestions, this may be worth a shot.
Good Luck
Shelly_D
petehall347
the brandy coffee man
whether voltage is actually plus or minus can help here .
Well this is super weird. I get home from the dentist (where I find out my dental implant needs to be removed and reseated deeper...cool) and the first thing I do is I remove the outputs and measure them with the meter and all measured good. So I swap them, left channel to right and right to left and I expected to see the same results after I powered it up. Instead both channels appear fine to a point. I can adjust bias on both channels and the dc offset on the right (one always been fine) is hovering around 30mv and the left is now at 70mv.
Should the outputs be replaced? What do you guys think is going on here? Should I switch them back to their original channels to see what happens?
Dan
Should the outputs be replaced? What do you guys think is going on here? Should I switch them back to their original channels to see what happens?
Dan
petehall347
the brandy coffee man
may have been cold solder .or possibly heat from soldering temporarily fixed an open output .
Q406
E -36.3v which is dead on
C -27.73v way too high (-14.19v)
B -36v which is good.
Q406 does not appear to be fully on (Vbe=0.3V), so volt drop
across R442 is not as expected causing higher collector voltage.
Maybe check D402 and C426, iff possible m,easure voltage at this point.
Intermittent problem, solder joint as above...
E -36.3v which is dead on
C -27.73v way too high (-14.19v)
B -36v which is good.
Q406 does not appear to be fully on (Vbe=0.3V), so volt drop
across R442 is not as expected causing higher collector voltage.
Maybe check D402 and C426, iff possible m,easure voltage at this point.
Intermittent problem, solder joint as above...
My thought was a cold solder joint as well and I completely went over the board with lighted magnifying glass. I’ll just resolder the board. By temporarily, you think I should switch out the outputs?
D402 was the only diode it did not replace, the RD5.6c. I have -36.9v anode and -31.44v cathode as of this morning.
I measured the voltages at Q406 again this morning and they’re still off.
Base I measure -35.0v, manual says -35.6v
Collector I measure -21.7v, manual says -14.19v (before I was measuring -27.73v so it has changed)
Emitter I measure -35.9v, manual says -36.3v.
I’m it this point going to power down, recheck every resistor and reflow the entire board. Should I swap out all of the ceramic resistors? I’ll get back after powering it back up.
Also, should I just remove Q406 (2sc1400) and replace it with one of the ksc1845s?
Dan
D402 looks ok (36.9-31.44=5.46V)
Q406 also looks reasonable, Vbe=0.9V high but...
The 2 likely scenarios are
- one of the outputs is breaking down/shorting
- failed component causing one half (+ or -) not to be turned on
Q406 also looks reasonable, Vbe=0.9V high but...
The 2 likely scenarios are
- one of the outputs is breaking down/shorting
- failed component causing one half (+ or -) not to be turned on
Note sign +/- of large dc "offset" voltage
teal'c
Nuclear Cardiac Parent
Or dogs.
Oldsansui441
Super Member
Damn dog, this is entirely the dog owners fault and you shouldn't have to wear ANY of the repair costs involved. I would be replacing all of the outputs and the drivers at a minimum. Check pre drivers and all resistor values on that board to be sure. Sounds like you have all of the diodes covered.
Alright, so I took part of the day and just completely rebuilt the amplifier board. I replaced every resistor, every ceramic capacitor, and every diode (with the exception of the RD5.6C) on both channels so they were uniform. I replaced all the 2SC1400s, but the rest of the transistors are stock along with the larger power resistors and stacked film caps. I know that was probably way overboard, but I’m done with this amp and just want to get it out of here.
One odd thing is I rechecked the transistors I put in and again Q404s gain had dropped a lot. Down to under 300 and I just put it in yesterday. Q402 was fine. Could there be something that is damaging Q404? Two brand new transistors put into that position have been pulled and measured to find the gain had dropped significantly.
On a plus note, the dc offset is sitting at about 3-4mv on the left channel and 5-6mv on the right. Lowest it has been.
Now I’ll just let it burn in and see how it goes.
Dan
One odd thing is I rechecked the transistors I put in and again Q404s gain had dropped a lot. Down to under 300 and I just put it in yesterday. Q402 was fine. Could there be something that is damaging Q404? Two brand new transistors put into that position have been pulled and measured to find the gain had dropped significantly.
On a plus note, the dc offset is sitting at about 3-4mv on the left channel and 5-6mv on the right. Lowest it has been.
Now I’ll just let it burn in and see how it goes.
Dan
You know I don’t know. When I left his place it was just setup on a table with some speakers so that he could here it before putting it in the final sitting place. When I went back the amp was up on a cabinet, too high for the dog to reach so not sure at what point his dog got to the wiring.
Dan
How stable is this amp, anyone know? On the terminals it says 8-16 ohm speakers and I’m guessing you could run both speakers A and B at the same time if they’re 8 ohms. He plans on running a pair of Infinity SS-2005s (6 ohm) and a pair of 8 ohm pioneers.
Dan
Dan
shelly_d
Not An Audiophool
That will produce a net impedance of about 3.4 ohms when both speakers are operating at the same time. Amps that say 8-16 ohms on the terminals are probably not real stable at those low impedances. I would caution against that.
Shelly_D
