• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Pioneer SX-980: in protect mode with over 40v for DC Offset (continued)

JoeDotCom

JoeDotCom

Super Member
This thread is a continuation of the thread originally posted in the Vintage Solid State forum, here:
Pioneer SX-980: popping noise on startup yesterday and now lights up but no sound
http://www.audiokarma.org/forums/showthread.php?t=388208
(I changed this thread title here so it better fits what is actually going on.)

After describing my problem, posting come pictures and getting some feedback from some helpful AKers, MTF posted...
markthefixer said:
1. remove output transistor connectors
2. remove any speaker loads from amp
3. power up amps, measure dc offset on both channels. amps are in dc balance (have correct feedback) without o/p transistors in place. TRY to zero using vr2, if no effect, return vr3 to original setting (measure it's ohms in circuit).

if not balanced (protection does NOT connect amps and speakers) then:

check driver transistors and their emitter resistors.

also check that the stv-4h diode leads are unbroken.

post q3,q4,q5,q6,q7 voltages... (ground referenced)

just a note, this is better served in the Pioneer Audio forum. Also mtf (me) is local to you...
I'm usually kept too busy to go round up strays in other forums.
Click to expand...


So I removed the connectors for the output transistors and do not have any speakers connected. Measuring DC offset on both sides of the amp gives me 20.7v and 20.9 volts respectively. Rotating vr2 yields no change in that voltage whatsoever.

If i reconnect the O/T transistor connectors and test again, i get between 40v and 50v. Rotating vr2 does seem to make a difference but only swings the voltage a volt or two.

so the system remains in protect mode.

MTF mentioned "return vr3 to original setting". I scoured the poweramp schematic and the board and I only see vr1 (for adjusting idle current) and vr2 (for adjusting dc offset) is there a vr3 I am missing somewhere?

(Also just for fun, i confirmed the idle current was still at 30mV with the transistors connected and 0 when they are disconnected)

the stv-4h diode leads look fine on both sides of the amp. (photo below)

Also I located q3,q4,q5,q6,q7 but i am not sure how to collect the voltages for you. Those are the driver transistors, right? When i measure them referenced to ground... i connect my meter to ground, and then a specific leg of the transistor? (or each leg on its own?)

If I am on the right track, then my next question is how to check the resistors. do I check the side of the resistor that is "away" from the transistor so we see what the voltage change is?


I really appreciate MTF and everyone elses help here and i look forward to hearing back on my questions above.

thanks a bunch, this if fun!

-Joe

2011-08-24_20-14-21_197-annotated%20(Medium).jpg

The SX-980 Power Amp Board
View Full Size Here
un-annotated version

2011-08-24_20-16-36_366%20(Medium).jpg

The SX-980 stv-4h diode
View Full Size Here
 
Last edited:
Register to hide this ad
Testing Voltages for Transistors. Black lead to Chassis. Meter set to DC Volts. Red lead to Base, Collector, and Emitter in turn. Write B, C, E on paper with the Q#. Then take a voltage reading and write it down. Move on to next lead.

Resistor Testing. Lift one leg (desolder and physically disconnect that side). Take reading of the resistor with meter on oHms Setting. Write down. Trying to take the reading in circuit will give erroneous readings as the rest of the circuit will show up also.

It takes time, and it's sometimes aggravating, but it's time well spent. With MTF busy as he is, the rest of us try and take up the slack some. Me myself, I'm still learning, but can do the basics. The above should get some #'s we can look at and recommend a course of action.

Larry
 
Quick followup question... should i be testing these transistors with the Output Transistors connected? (Does it make a difference?)
 
At this point I'd leave the output's disconnected. Also read Echowars treatise on Testing BJT's on the DIY or General Audio Forums. (It's been a while since I've lookedit over. POST #11 is what you want here) This will be used to test the output's to see if good or bad. (edit: here's the link) http://www.audiokarma.org/forums/showthread.php?t=43186

As for the (vr3???) i think he made a typo and was referring to VR2.

Get the voltages and check back.

Larry
 
Last edited:
Awesome. thanks again Larry. I had read that thread a few days ago but will reread it now that i will be able to understand it a bit better. :)

I was anxious so i already tested q3,q4,q5 since I can get to them without removing the circuit board (which i realize I will need to do in order to unsolder the resistor legs for testing. (one leg per resistor)

Here is the first set of numbers....

q3: b: 2.1v c: 47.3v e: 1.4v
q4 b: 2.1v c: 10.0v e: 1.4v
q5 b: 49.8v c: 50.4v e: 50.5v

Interesting about q4... the collector took about 2 minutes to reach that voltage. when i flicked the power switch on after attaching my lead, the voltage slowly rose to 10. all the other values stabilized within a second or two.

I will go back and remove the board and get the q6,q7 and emitter resistor values for ya'll shortly.

Should i do these same measurements for the other side of the amp?


Another (possibly noobish) question... I have only tested one side of the power amp section so far. But is it weird that both sides are exhibiting the same symptoms? that doesn't point to the problem being elsewhere so that it would be impacting both sides of the amp?

again thanks to all!!!

2011-08-24_22-06-33_126.jpg

testing the q4 base
 
When BOTH channels are misbehaving in the same manner, look to a common fault.

In this case look (on the amplifier card) for:

pin 12 +52v DC UN regulated
pin 8 +50.0v DC regulated
pin 4 +23.0v DC regulated
pin 5 -23.0v DC regulated
pin 1 -50.0v DC regulated
pin 21 -52v DC UN regulated

actually when anything is misbehaving, the first thing is to check all the power supply voltages.

vr3 was a typo - meant vr2

IF the 4 above voltages are not within 10 % of expected values, don't bother taking the transistor voltage readings.

I have NOT read every post on this thread tonight, just the first few.
 
Last edited:
markthefixer said:
actually when anything is misbehaving, the first thing is to check all the power supply voltages.
Click to expand...

Thanks MTF, I will go over those voltages before deciding to go on to the transistors.


markthefixer said:
In this case look (on the amplifier card) for:

pin 12 +52v DC UN regulated
pin 8 +50.0v DC regulated
pin 4 +23.0v DC regulated
pin 5 -23.0v DC regulated
pin 1 -50.0v DC regulated
pin 21 -52v DC UN regulated
Click to expand...


when i go to look for these pins on the "amplifier card" is the same board I have been working with? the Power Amplifier Assembly (AWH-073)? I was expecting to need to tinker with the power supply card. I just want to be sure i am messing w/ the right pins and that I have my terminology straight. :)
 
Yes the AMP Card(s). That is the AWM 073 (board)card(s). These pins are the power leads from the Flat amp, protection board, and the power supply. Getting the voltages here is easier than flipping the unit over and around to get voltages from other spots.

Eventually you may end up working on the Power supply board.

My overiding question right now is and I'm not trying to dis ya. You DO have a copy of the Service Manual with schematics and can read them at least enough that we can walk you thru it? If not the AK Database should have it. If not PM me.

Larry
 
larryderouin said:
Yes the AMP Card(s). That is the AWM 073 (board)card(s). These pins are the power leads from the Flat amp, protection board, and the power supply. Getting the voltages here is easier than flipping the unit over and around to get voltages from other spots.

Eventually you may end up working on the Power supply board.
Larry
Click to expand...
That is what i though / hoped. Thanks. I will get those measurements tonight.

larryderouin said:
My overiding question right now is and I'm not trying to dis ya. You DO have a copy of the Service Manual with schematics and can read them at least enough that we can walk you thru it? If not the AK Database should have it. If not PM me.
Click to expand...
No dis perceived. I am very open to admitting THIS IS MY FIRST TIME WORKING INSIDE A RECEIVER. :)

Yes, I have the service manual (downloaded from http://www.hifiengine.com/manuals/pioneer/sx-980.shtml ) Though the diagrams are kinda hard to make out. If you had a sharper copy of the specific circuits we are working on here i would love to have them.

I took electronics in highschool and recognize the symbol for resistors and capacitors, etc. But I never learned about transistors and other more advanced stuff. So I have been doing a lot of reading here on AK these past few days. I am confident w/ a soldering iron in my hand, though i have not worked w/ circuit boards much. I am knowledgeable enough to get through this as long as I have some adult supervision (even though i am in my 30's. haha.) and every interaction I am having with you guys is making me even better at this. :)

I am VERY thankful for the guidance and i do understand that you awesome people are helping in multiple threads. I am trying to think for myself a bit as you are guiding me and trying to keep my personal "logic" circuits running so i can understand what I am doing and why I am doing it. So I hope nobody takes my followup questions as defiant or mistrusting. It is just me soaking in and really trying to understand the process we are going through so I can be even better the next time.

In the forum world, i read once that there are three levels of participation most users go through (paraphrasing here)...
1) The Lurker: I read only and hope someone else has already asked my question.
2) The Asker: Now I will ask my own questions and seek answers for myself.
3) The Helper: Now I know enough to help others find answers.

I hope one day to reach that 3rd level. So I am soaking in all the knowledge I can. :)

:thmbsp:

-Joe
 
markthefixer said:
When BOTH channels are misbehaving in the same manner, look to a common fault.

In this case look (on the amplifier card) for:

pin 12 +52v DC UN regulated
pin 8 +50.0v DC regulated
pin 4 +23.0v DC regulated
pin 5 -23.0v DC regulated
pin 1 -50.0v DC regulated
pin 21 -52v DC UN regulated

actually when anything is misbehaving, the first thing is to check all the power supply voltages.

vr3 was a typo - meant vr2

IF the 4 above voltages are not within 10 % of expected values, don't bother taking the transistor voltage readings.

I have NOT read every post on this thread tonight, just the first few.
Click to expand...


OK, got some numbers. all readings were near spec except pins 1 and 5 which were nearly zero. I am going to start poking around and see if i can focus on what feeds those pins and look for signs of damage. The right track? :)

pin 12 +51.7
pin 8 +50.6
pin 4 + 23.7
pin 5 +0.7 <-----
pin 1 +0.8 <------
pin 21 - 51.3
 
Well, you found the problem, and the -23v depends upon the -50v to be there first.

no poking around.... please...

get familiar with looking at the power supply board.

q4 is a power pass element

q3 is a feedback amplifier

d9 is a -13v reference supplied to Q3's emitter

q3 wants to keep 13.6v at it's base, so it varies it's collector to emitter current to do so. That collector to emitter current drives the series pass transistor q4 to let a voltage through to it's emitter (-50v) which then the r15/r14 voltage divider divides down to -13.6

thus q4, q3 and d9 get replaced. also some new capacitors won't hurt, and the death of a cap could have caused the problem. if so I hope that cap is on the power supply board.

it could be as simple as q4 being baked to death. need to get some thermal paste to mount the transistor.

i'm gonna have to get a parts list together for this. Hopefully before sunday night, (it's thurs nite so ordering it on friday won't help to get it here any faster).
----------------------------------------------------------------------
edit: I had one, now to make sense of it:

q1 2sd712 npn to-220 bce 100v 4a 30w 55-300hfe 8mhz

q2 2sc1735 npn to-92 bce 100v 0.5a 0.8w 50-300hfe 130mhz

q3 2sa850 pnp to-92 bce 100v 0.5a 0.8w 50-300hfe 130mhz

q4 2sb682 pnp to-220 bce 100v 4a 30w 55-300hfe 8mhz
512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54

Q5 2sd712 npn to-220 bce 100v 4a 30w 55-300hfe 8mhz
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54

Q6 2sc945 npn to-92 ecb 60v 0.1a 0.25w 50-600hfe 150mhz
512-KSD1616ALBU to-92 ecb 160v 1a 0.75w 160mhz 135-400hfe $0.09

D8 mz140
512-1N5244B Fairchild 14 V, 0.5W Zener

d9 mz130
512-1N5243B Fairchild 13 V, 0.5W Zener

d10, d11 LZ230
512-1N4748A Fairchild 22 V, 1.0W Zener

substitutions:

q1 2sd712 100v 4a 30w 55-300hfe 8mhz
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54

q4 2sb682 100v 4a 30w 55-300hfe 8mhz
512-KSA940TU pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
neither side is going to come close to an amp of current, no less 4 amps


q2 2sc1735 100v 0.5a 0.8w 55-300hfe 130mhz
512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17
q3 2sa850 100v 0.5a 0.8w 55-300hfe 130mhz
512-KSA1013YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17 (R=60-120, O=100/200, Y=160/320)


Q5 2sd712
512-KSC2073TU

q6 2sc945a eCb 50v .15a .25w 300mhz 40-700hfe
512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17

d8 mz-140 512-1N5244B Fairchild 14 V, 0.5W Zener
d9 mz-130 512-1N5243B Fairchild 13 V, 0.5W Zener



c19,c20 4.7uf 50v 647-UPW2A4R7MDD 4.7uf 100v $0.14
c17,c18 47uf 16v 647-UPW1V470MED 47uf 35v $0.16
c24,c25 47uf 25v 647-UPW1V470MED 47uf 35v $0.16
c11,c12,c15,c16 220uf 80v 647-UPM2A221MHD 220uf 100v $1.02 ea
c13 220uf 35v 647-UPW1V221MPD 220uf 35v $0.28
c23 2200uf 35v 647-UPW1H222MHD 2200uf 50v $1.49 ea


you will need some thermal paste to mount the power transistors:
532-249 1 oz thermal compound $6.45

---mouser bom tool --- entry text block ------
512-KSC2073TU
512-KSA940TU
512-KSC2383YBU
512-KSA1013YBU
512-KSC2073TU
512-KSC2383YBU
512-1N5244B
512-1N5243B
512-1N4748A|2
647-UPW2A4R7MDD|2
647-UPW1V470MED|4
647-UPM2A221MHD|4
647-UPW1V221MPD
647-UPW1H222MHD
532-249


eleven bucks parts, 6.50 for thermal paste, all in stock at 11 pm thurs...
 
WOW.

that is some amazing info there MTF. wow.

I am going to read this a few times, then read again with them service manual in front of me, then again sitting above the circuitboard. wow.

SO i have my next action steps right... i can use the BOM tool on mouser.com and order all these parts. (already imported, that is an awesome import tool!)

order the parts ASAP. (tomorrow AM)
**I also need to get a solder sucker tool. :)

then once they arrive check in here and let you know i am beginning work. I can remove the screws from the power supply board (being careful of the wire connections) and begin replacing the components. Can i just do q4, q3 and d9 to start to see if she will power back on and then do the caps 1 at a time verifying she still works after each one? I guess what I am asking is can i break this list of items to install into smaller chunks so i can verify she is working and then do the caps making sure i dont re-break anything? Or will it be safer to replace this whole list at once? (or am i getting ahead of myself altogether?)


I am super grateful for this assistance! (and this is fun!!!)

-Joe
 
balancing risk and exploring/learning, I'll delineate the fix parts INCLUDING some caps, then the rest for "beefing up".

learn / refresh emitter base and collector lead designations, and how only 1 of 6 ways to install a transistor will actually work. learm\n the symbol and how it identifies ebc layout and how to install at THAT location.
 
JoeDotCom said:
Bummer, maybe next year. :)

OK parts order is in. Thanks for making that so easy. I was worried about how i was going to get an accurate parts list together. :thmbsp:
Click to expand...

What's this "next year" bupkus, LOTS of local AK'ers have visited the fixer's lair, a far more interesting experience....

p.s. It's WAY past my "bedtime"....
 
markthefixer said:
What's this "next year" bupkus, LOTS of local AK'ers have visited the fixer's lair, a far more interesting experience....

p.s. It's WAY past my "bedtime"....
Click to expand...
Sign me up, I'll bring beer!

bedtime: what the!?! I hope you don't work a 9-5 on top of all the forum work you do.
 
You must log in or register to reply here.
Back
Top Bottom