Pioneer SX-980: in protect mode with over 40v for DC Offset (continued)
- Thread starter JoeDotCom
- Start date
JoeDotCom
Super Member
My Parts should arrive today!! I am super excited to get started. I have been studying the service manual and learning about the right way to install a transistor. I will wait to get my task list / order from MTF before i dig in. I cant wait to get this thing powered back up... and then move on to BEEFING IT UP!
(welcome lurker Thomas.
)
sipuser
Well-Known Member
Hey Joe,
Good luck on your repair job.
This is good timing (for me), I also have a 980 with problems.
Using one of markthefixer other threads on 980's I've traced the problem to the power supply board, but haven't had time to order parts and start the repair process.
You can learn alot from reading all the AK threads on a particular unit.
Good luck on your repair job.
This is good timing (for me), I also have a 980 with problems.
Using one of markthefixer other threads on 980's I've traced the problem to the power supply board, but haven't had time to order parts and start the repair process.
You can learn alot from reading all the AK threads on a particular unit.
JoeDotCom
Super Member
Thanks. I am super thankful for all the help I have had so far. And I am hoping that if i continue documenting my process clearly it will be a good reference/inspiration for others.
you should NOT power up without one, especially after amplifier work.
it will save the output transistors from inadvertent damage.
there will be a LOT more discussion before powering up the unit after ANY work.
it will save the output transistors from inadvertent damage.
there will be a LOT more discussion before powering up the unit after ANY work.
Dim Bulb Tester ( DBT ) Follies
The thing to remember is that the equipment that is connected to the dbt can do strange things because of the reduced AC voltage the unit is "seeing". The brighter the bulb, the lower the AC voltage at the unit.
It may be enough that the protection circuit thinks that the AC is turned off....
OR, as idle current is increased (part of testing) and the bulb grows brighter the AC dips below that "magic" protection circuit threshold. It CAN induce butterflies when that happens.
Also while adjustments are done while "under the bulb", they will be in error when the unit is connected straight to the power line.
Of these adjustments:
Offset can be adjusted into the ballpark
BUT
WE NEVER LEAVE IDLE CURRENT SET ANYWHERE BUT THE MINIMUM WHEN TRANSITIONING FROM THE BULB TO THE POWER LINE.
That is because this fresh infusion of FULL AC voltage WILL cause that idle current setting done on the DBT to be WAYYY too high off the bulb.
But we do test the idle current one channel at a time ON the DBT, trying to turn it up to the indicated reading to see if we can tease out any nasty responses while under the safety (and complication) of the bulb. We may NOT get high enough idle current because of the reduced AC voltage while "under the bulb" but it's better than nothing.
THEN we turn back down the idle current on each channel after the test.
to power up a unit, thumbnail of ideal sequence ONLY, there will be variations and decisions/exceptions (none major - especially for idle current):
connect the dbt
turn it on
after it dims, try to adjust any adjustable power supply voltages (only a few units have this)
try to adjust the offset voltages down to zero
one at a time, try setting (then turning back down) the idle current.
if none of these causes the DBT to go on "hard", then:
connect to AC line directly
set any power supply voltages for real
set any offset voltages for real
set any idle current settings for real
go back after 20 min or so of "soak time" and tweak offset and idle.
The sequence of power supply, offset then idle adjusts is paramount, BECAUSE the power supply adjustment affects the offset voltage.
Thus as the power supply warms up, the offset WILL drift a bit - it is unavoidable.
As the output transistors warm up, the idle current will drift a bit, it is also unavoidable.
The thing to remember is that the equipment that is connected to the dbt can do strange things because of the reduced AC voltage the unit is "seeing". The brighter the bulb, the lower the AC voltage at the unit.
It may be enough that the protection circuit thinks that the AC is turned off....
OR, as idle current is increased (part of testing) and the bulb grows brighter the AC dips below that "magic" protection circuit threshold. It CAN induce butterflies when that happens.
Also while adjustments are done while "under the bulb", they will be in error when the unit is connected straight to the power line.
Of these adjustments:
Offset can be adjusted into the ballpark
BUT
WE NEVER LEAVE IDLE CURRENT SET ANYWHERE BUT THE MINIMUM WHEN TRANSITIONING FROM THE BULB TO THE POWER LINE.
That is because this fresh infusion of FULL AC voltage WILL cause that idle current setting done on the DBT to be WAYYY too high off the bulb.
But we do test the idle current one channel at a time ON the DBT, trying to turn it up to the indicated reading to see if we can tease out any nasty responses while under the safety (and complication) of the bulb. We may NOT get high enough idle current because of the reduced AC voltage while "under the bulb" but it's better than nothing.
THEN we turn back down the idle current on each channel after the test.
to power up a unit, thumbnail of ideal sequence ONLY, there will be variations and decisions/exceptions (none major - especially for idle current):
connect the dbt
turn it on
after it dims, try to adjust any adjustable power supply voltages (only a few units have this)
try to adjust the offset voltages down to zero
one at a time, try setting (then turning back down) the idle current.
if none of these causes the DBT to go on "hard", then:
connect to AC line directly
set any power supply voltages for real
set any offset voltages for real
set any idle current settings for real
go back after 20 min or so of "soak time" and tweak offset and idle.
The sequence of power supply, offset then idle adjusts is paramount, BECAUSE the power supply adjustment affects the offset voltage.
Thus as the power supply warms up, the offset WILL drift a bit - it is unavoidable.
As the output transistors warm up, the idle current will drift a bit, it is also unavoidable.
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JoeDotCom
Super Member
I am glad I got to cut my teeth on the bias and idle current settings on this receiver during the few weeks when it was working. I would be kinda nervous making the adjustments if I had not learned about adjusting them previously.
(just for reference and to tie it all together, here is the link where EchoWars, ryuuoh, and a few others help get my DC offset and idle current into usable shape. My New Pioneer SX-980, but afraid to use it... (DC offset high?!?) )
(just for reference and to tie it all together, here is the link where EchoWars, ryuuoh, and a few others help get my DC offset and idle current into usable shape. My New Pioneer SX-980, but afraid to use it... (DC offset high?!?) )
JoeDotCom
Super Member
Hi ToTek,
It is going well. i have not started replacing anything yet. I just built my Dim Bulb Tester in preparation of the work and am about ready to start on the rapair. As you can see above i am receiving help from the magical and fabulous MarkTheFixer, and from the look of his recent post activity he has a big list of folks he is working with currently. So, I am in his queue waiting for his input to get started. Hopefully it will be soon, but I am not in a big rush, and i am super thankful for the help so i dont mind waiting.
Good luck with your recap once you find time. take pics / document. it is awesome to see.
-Joe
It is going well. i have not started replacing anything yet. I just built my Dim Bulb Tester in preparation of the work and am about ready to start on the rapair. As you can see above i am receiving help from the magical and fabulous MarkTheFixer, and from the look of his recent post activity he has a big list of folks he is working with currently. So, I am in his queue waiting for his input to get started. Hopefully it will be soon, but I am not in a big rush, and i am super thankful for the help so i dont mind waiting.
Good luck with your recap once you find time. take pics / document. it is awesome to see.
-Joe
Hi ToTek,
It is going well. i have not started replacing anything yet. I just built my Dim Bulb Tester in preparation of the work and am about ready to start on the rapair. As you can see above i am receiving help from the magical and fabulous MarkTheFixer, and from the look of his recent post activity he has a big list of folks he is working with currently. So, I am in his queue waiting for his input to get started. Hopefully it will be soon, but I am not in a big rush, and i am super thankful for the help so i dont mind waiting.
Good luck with your recap once you find time. take pics / document. it is awesome to see.
-Joe
what's the hold up? basic questions can be answered by MANY "fixers" (in training
) here...
JoeDotCom
Super Member
I just wanted to be sure I had heard you out before i jumped in. Being new at this, I want to be sure I go about this the right way and take my time.
so....
So I think my plan is to replace q4, q3 and d9 all at once. Then can I power it on using the DBT? How do I confirm it is working OK? Set Idle, and DC offset? Then do i try to get signal out of the speakers? (All the while watching for the bulb to go bright signalling a problem)?
Then once i have the 3 above replaced and happy... can i just work across the circuit board replacing the other items to beef things up?
C16
c18
c20
c25
q4
q3
d9
come up on the dbt and measure (from page 1) pins 27 (pin 1 on amp) -50v dc and pin 26 ( pin 5 on amp card) -23v dc
adjust offset on amp(s) using vr2 (100k ohms) to 0.000 volts dc (read pin 10 on amp : red dmm lead, ground : black dmm lead)
(note: still on dbt)
do the rest of the power supply replacements
if and when you change D11 on the power supply board, the -23v will change a bit and affect your zero setting, unavoidable.
the same applies for a bunch of parts used in the +50v regulator.
you can check idle current for now, don't adjust it even off the bulb until we talk. adjusting offset multiple times is fine, on or off the dbt.