SX-3900 Powers on, but no audio output...

I just got to sit at the work bench today with my newly acquired SX-3900 receiver and was able to at least bring it to life. When I got it, it did not power on. I replaced the blown 10A fuse and powered it up, and it blew within one second. I removed the bottom cover and noticed that one of the connectors to one of the transistors mounted to the Large Heat sink fins was broken and one of the pins was grounding out on the heat sink. I reattached the wire and used electrical tape to ensure that it was isolated and installed a new 10A fuse and it now powers on and stays on. The protection relay does not energize though. And no sound from either the headphones or speakers.

I pulled the pre-amp jumpers and connected it to another power amp and all preamp functions appear to work fine. The tuner works and I was able to listen to FM and AM stations, and I had a CD player connected to the AUX In and it worked fine with the pre-amp portion.

I used another thread (from May 2007) in which markthefixer assisted garagmahal with his SX-3900, that had the same problem.
http://www.audiokarma.org/forums/showthread.php?t=113309

I got to a certain point and found that there were a few voltage issues, listed below:

On the Power Supply Board I checked these points (to Ground):

22s = +55vdc
20u = -55vdc
23b = 0vdc
24a = -32vdc
19e = +13vdc
11d = 0vdc
D6 = +14vdc (across it)
Q1 - 55-33-0
Q3 = 56-55-73 (Heatsinked)
Q4 = 56-56-73

There also appears to be another Q3 transistor, which measured 0-0-0 (non-heatsinked)

I found what appeared to be a couple of cold solder spots on the Q1 and Q3 and hit them with a touch of solder. I powered it up and the voltage readings were the same. Then I noticed the Q1 transistor begin to put off smoke and I powered the unit down.

The PCB appears to have had some high levels of heat (discoloration) around the Q1 and Q3 areas, mostly the Q1.

Any thoughts? Thanks for any help.

Thanks markthefixer for your advice on my other post about the problem I am having. I figured I would post my other reply here as well, to get this thread back on track.

Thank you for the information. I located an issue on the Power Supply PCB, it was the Q3 transistor with a burned and disconnected trace. I decided to go ahead and prep the unit for a complete recap... It will be a huge undertaking. This is the reason I thought of going ahead and re-doing the wiring/wire wraps.

Does the power supply board need to be fully connected to the other boards to test the voltages on it? Or can it be checked thoroughly with just the power coming from the transformer and rectifier board? I ordered all transistors and caps for the Power Supply board to rebuild it completely, due to that burned Q3 and some other signs of excessive heat.

You want to do a MINIMUM of disconnecting. And the replacements for the 2sk34's are only available (that I could find) from ampslab.com at 20 for $20.

Fairchild just obsoleted the ksk30, which was one of the last substitutes avilable.

It looks like I'm going to have to research current regulator diodes much sooner than I expected, as these should replace the function performed by the 2sk34's in the power supply. (at about 2 bucks apiece....)

what did you order for q1 and 12 on the power supply?

markthefixer said:

You want to do a MINIMUM of disconnecting. And the replacements for the 2sk34's are only available (that I could find) from ampslab.com at 20 for $20.

Fairchild just obsoleted the ksk30, which was one of the last substitutes avilable.

It looks like I'm going to have to research current regulator diodes much sooner than I expected, as these should replace the function performed by the 2sk34's in the power supply. (at about 2 bucks apiece....)

what did you order for q1 and 12 on the power supply?

Click to expand...

I jumped the gun a bit on my post, thinking that I had the parts all located, but the 2SK34 seems to be a bit hard to locate, if not impossible.

For the Q1 and Q2 (2SK34) I found a cross reference part from NTE, the NTE312 or NTE459, but have read negative things about the quality of NTE components. (yay or nay) Is this a suitable substitute for this part? I didn't see them listed (at least as 2SK34) on the ampslab website. Thanks.

EDIT: Sorry, I see in another thread that you state that the ampslab part is the 2SK30. Is that a suitable replacement for the 2SK34? I also found a 2SK30A that is stated as being a replacement... How bout that one? I also see there appears to be a voltage difference in some of these (30 vs 50)... Thanks again.

There's a bunch of power supplies down right now, all with suspect 2sk34's used.

It looks like I need to do some experimenting to see if current regulator diodes will replicate the function that the 2sk34 does. I primarily need to figure out the correct current to specify.

THEN I can name a specific current regulator diode that's about $2.50 to use. Since the diode is rated for 100v as opposed to 50 or 30 we then should be in good shape.

610-1N5306 $ 2.45 this is a 2.2 mA current regulator diode, and may be able to substitute for the 2sk34 in that power supply function.

That's a little easier, (and perhaps less expensive) than the current source that EchoWars put together for the sx-1980.

You see, there's just so many 2sk34's left in the world, and I'd rather see them used in the amplifiers, and let something else shoulder the load in those power supplies.

Later I will look at the amps and see if they really need 50v jfets, or if 30v jfets (common) will do as well.

Thanks Mark, I will anxiously await your research and findings in regard to this known issue and a feasible workaround. Seems very true in what you say, because this particular Power Supply board had previously had the 2SK34 (Q1) replaced at least once, and it has heat discoloration on the PCB all around the area of the 2SK34 (Q1) and the Q3.

Is the KSK30 or 2SK30 (or 2SK30A) a workable substitute for the 2SK34 in the meantime? I know that it may succumb to the same deadly fate as the 2SK34 in that spot, but was just curious. Would certainly rather have a long-term fix for the problem.

Thanks for your knowledge and assistance.

Located this, in reference to the 2SK34. I RFQ them on it... This company is right down the street from me. They have a high minimum order requirement though.

http://www.4starelectronics.com/part_detail/2SK34.html

ksk30 is a tried and true substitute. And it is assuredly 50 volts.

4star won't go with a small quantity, I'd almost bet they don't have them locally, if they are even in their possession, rather than them being a broker who has to go FIND them.

The "current regulator diode" is nothing more than a jfet junction with the source and gate connected together, like Pioneer does on the printed circuit board.

So it's nice to have a 100v overhead instead of 50 (or 30).

It would be prudent to get the mouser.com part number 610-1N5306 @ $ 2.45 this is a 2.2 mA current regulator diode, and may be able to substitute for the 2sk34 in that power supply function.

I didn't just pull a number out of a hat, EchoWars made a substitute circuit for the sx-1980's 80v regulator that originally uses the EXACT SAME 2sk34 as the one used in your power supply, and he determined that a current of 2.2 milliamps was the design objective for his replacement circuit.

I just have to establish if there are any variations in operation of a 2sk34 set up as a current regulator diode and an ACTUAL current regulator diode, by actual experimentation. I expect NONE - I'm just being my usual picky self....

EchoWars 's circuit is more appropriate for the 1980 because the 1980's regulated voltage is almost 100 volts, and depnding upon the transistors he uses to build it, it could withstand 150 to 250 volts.... which we don't need, 100v is quite enough....

markthefixer said:

ksk30 is a tried and true substitute. And it is assuredly 50 volts.

4star won't go with a small quantity, I'd almost bet they don't have them locally, if they are even in their possession, rather than them being a broker who has to go FIND them.

The "current regulator diode" is nothing more than a jfet junction with the source and gate connected together, like Pioneer does on the printed circuit board.

So it's nice to have a 100v overhead instead of 50 (or 30).

It would be prudent to get the mouser.com part number 610-1N5306 @ $ 2.45 this is a 2.2 mA current regulator diode, and may be able to substitute for the 2sk34 in that power supply function.

I didn't just pull a number out of a hat, EchoWars made a substitute circuit for the sx-1980's 80v regulator that originally uses the EXACT SAME 2sk34 as the one used in your power supply, and he determined that a current of 2.2 milliamps was the design objective for his replacement circuit.

I just have to establish if there are any variations in operation of a 2sk34 set up as a current regulator diode and an ACTUAL current regulator diode, by actual experimentation. I expect NONE - I'm just being my usual picky self....

EchoWars 's circuit is more appropriate for the 1980 because the 1980's regulated voltage is almost 100 volts, and depnding upon the transistors he uses to build it, it could withstand 150 to 250 volts.... which we don't need, 100v is quite enough....

Click to expand...

Please forgive me if I sound like a bonehead, but I know just enough about electronics to be dangerous. BUT I AM PASSIONATE ABOUT THIS LEARNING EXPERIENCE AND WANT TO GET THIS RECEIVER IN TIP-TOP SHAPE. Kind of a personal vendetta of mine, as I owned a brand new SX-3800 when I was in high school. My wife thinks I have gone nuts (but is very supportive of my new addiction), all the time I have been spending on this project!

I see that the Q1 and Q2 (2SK34) share the pins on the PCB. I would love to be able to put the 610-1N5306 Mouser Current Regulator Diode in place of them. And I certainly trust your strong hypothesis. Just would like to hear from you that it is a proven substitute, but I know in regard to vintage electronics, nothing is definite...

If I go with the 2SK30A-Y (20 for $20) at Ampslab, would that also work for the 2SK34 (Q1 and Q2)? I know you mentioned before that it was a replacement for it, but just wanted your advice on whether I should go that route, or do the diode as a replacement, upon your go-ahead? It seems like you are leaning toward the diode in the Q1 and Q2 spots, with the 100v overhead...? Longevity is the key.

Also, when I check the diode at D11, it appears to be bad. It is not OL (open lead) on that diode. Just wondering if I am checking it correctly. All other diodes on the board check out fine with OL indications. Any thoughts?

I also checked all the resistors (27 of them) and they all seem to check perfect, or very close. I had to lift one end of a few of them. Would it make sense to go ahead and replace the resistors while I have this thing out? It would be pretty cheap and fairly quick to do.

It looks as though the board has three 1-watt, four 1/2 watt and the rest 1/4 watt resistors. Am I on track with this? If so, what are the best kind to get for replacement?

I would just like to ensure that the power supply board along with the rectifier board are doing exactly what they should do, and that they are as fresh as possible to deliver the rest of the receiver with good clean power.

Thanks again!

For right now, if you don't mind the outlay for 18 extra fets from ampslab ( I think while I was getting them I paid all of $0.10 in quantity, until they became much less obtainable) go with the ampslab parts.
Partly because I'm a frugal bastich, and partly because they have become a hard to obtain part, and I don't want to encourage wasting them in a power supply when something that IS still being made can do the job.
I loved an old commercial for some sort of potato chips - "eat all you want, we'll make more!!!"

OK, we are focusing on the power supply repair. Which parts DO you have (or have incoming), you can link to a thread with a parts list if that's what you used. Hopefully a list I posted, with some caps having higher voltages, which are less likely to be killed during a power supply fault. Also some transistors (Q7 & Q8) are more robust, they are run HOT in the original.

The EASIEST way to fix a power supply is to use all new transistors, diodes and caps - a "shotgun approach".
The caps dry out, so it is worthwhile to just replace them. pretty much all under a buck, most much less.
and a piecemeal transistor replacement may hurt the replacement transistors and diodes - confusing the issue.
Plus most are REALLY inexpensive, less than a dime for some transistors and diodes, less than a buck for Q3, Q5, Q9, Q11

Your particular problem MAY be something off board that is pulling too much current from one of the supplies. Most typically it is a shorted (or failing in the process of shorting - and getting hot - capacitor.
That's why you pull the wires sending the power off the board, to interrupt the current to allow you to fix the supply. Then you stick a resistor in line to limit the amount of current flowing (and NOT blow the regulator you just fixed) and find the problem.

I am willing to explain HOW the regulator(s) work, BUT it would be a HUGE amount of typing. Suffice it to say that the 14v zener D6 is the key to it ALL, with Q3 and Q4 performing a see-saw balancing act. a transistor LIKES to keep 0.6v (neg or pos depending upon npn or pnp) between it's emitter and base, and the circuits exploit this fact to work.
Q4 emitter is at 14v because of D6. Q4 base is at 14.6v because R19 and R10 step the 54v down at a particular ratio - they're a voltage divider. If the Q4 e-b voltage is less than 0.6 the transistor shuts off allowing it's collector voltage to rise, which raises Q3's base voltage , which raises Q3's emitter voltage until there is a 0.6v difference between base and emitter. eventually q3 is turned on enough (base = 54.6v) that the emitter hits 54v and that gets 14.6 at Q4's base which gets everything in balance. If the load changes, the 54v rises or drops, changing Q4's voltage again until it gets back 14.6v at the base and 54v out.

Q1 should only make a difference at powerup, C7, C5, C10 keeps the circuit from oscillating, Q7 is a separate regulator that delivers a percentage of it's input. The negative 54v regulator is a mirror image without the zener, and it wants -0.6v at the base of Q5, but IT'S reference divider (R11,R12 and R13) is connected not to ground like R9 & r10 but to the positive voltage, and arranged so that at +54v and -54v the base of Q5 is at -0.6v.
This is a TRACKING regulator, that mirrors the positive voltage with the negative. Q8 is another proportional regulator, made for the opposite polarity.
Q9 & Q10 steal a sample of the 14v from the zener, and use it to control the 12.8 v supply (14.0 - 0.6 (Q9) - 0.6 (q10) = 12.8V). so if the 14v from the zener is messed up, so is thais voltage, OR it can HURT the 14v zener if IT shorts out.
Q11 is a 5.5v regulator that has a 6.1v reference made by a voltage divider (12.8 to 6.1 OR zero!!) on another board and coming back to it. This is so some other board can shut down the 5.5v and turn off some circuits when they are not being used.

This is a lot to chew on, and some of this may need some lookup on wikipedia.

The nice part about a power supply is it's less finicky than some audio circuits as far as replacement transistors.

I will get the 2SK30 (Qty of 20) from Ampslab tomorrow. I will do the "shotgun" approach to the Power Supply board for sure. I want to make sure I get it right and solid.

Your explanation of the regulator functions made my head spin! You certainly have your head around this whole process, no doubt.

So far, I don't have much firmed up as far as parts go, unfortunately... But here is what I have researched thus far. I have not purchased any of them:

Caps
C23 CEA 471M 16L 470uF 16v Replacement part= 647-UPW1E101MED
47Uf 63v, Replacement= 647-UPW2A470MPD
100Uf 25v, Replacement= 647-UPW1E101MED

Transistors/Diodes
Q1, Q2 2SK34, Replacement= 2SK30A-Y (from ampslab)
Q10 2SC2575, Replacement= 512-KSC2383YBU
Q4 2SC1885, Replacement= KSC2310
Q6 2SB682, Replacement= KSA614
Q7 2SC1915, Replacement= KSC1845
Q8 2SA905, Replacement= KSA910 or KSA992
Q9, Q11 2SD313, Replacement= KSD880
D1, D11 1S1555, Replacement= 1N4152 or 1N4150

And that is really as far as I got. Not too much I know.

I think for the caps, I might be able to figure them out. Should it be OK if I bump up the voltages a bit? Say if the OEM is 50v, bump it to 100v? Maybe double or so?

It's the Transistors that are killing me for finding the alternate parts.

Thanks again.

You've done pretty good, I KNEW I had done this recently:

http://www.audiokarma.org/forums/showthread.php?t=187712

The sx-d7000 power supply is VERY close to the sx-3900's power supply - there's a few gotcha's but you can use that thread for what you seek.

Download the 3900 power supply diagram / svc man and compare IF the Q number designations are different, the 5.5v reg is a 8.6v integrated circuit, but the transistors are the same parts.

The capacitor lists have: part designation, capacitance, voltage pioneer used, MY voltage recommendation (a few are more due to availability/price as opposed to longevity) and the mouser part number. You got pretty far with your last post, so this should be easier.

markthefixer said:

sx-d7000 awr216 power supply parts..... messy but complete

mouser.com parts numbers
nichicon upw caps, fairchild transistors, I.C. and diodes
cap uf spec v real v part number each subtotal
c3,4 220 80 100 647-UPW2A221MHD 1.26 2.52
c10,11 47 63 100 647-UPW2A470MPD 0.48 0.96
c23 10 63 100 647-UPW2A100MED 0.25 0.25
c12,13 47 50 50 647-UPW1H470MED 0.25 0.5
c16 10 50 50 647-UPW1H100MDD 0.16 0.16
c5 2.2 50 50 647-UPW1H2R2MDD 0.14 0.14
c18 1000 35 50 647-UPW1H102MHD 1.26 1.26
c17 100 35 50 647-UPW1H101MPD 0.36 0.36
c20 100 35 50 647-UPW1H101MPD 0.36 0.36
c9 100 25 50 647-UPW1H101MPD 0.36 0.36
c19 100 25 50 647-UPW1H101MPD 0.36 0.36
c15 2200 16 35 647-UPW1V222MHD6 1.71 1.71
c22 220 16 35 647-UPW1V221MPD 0.41 0.41
c2 3300 10 25 647-UPW1E332MHD6 1.33 1.33
c21 470 10 25 647-UPW1E471MPD6 0.55 0.55



d6 512-1N5244B 0.05
d13 512-1N5244B 0.05
d12 512-1N4148 0.03
d14 512-1N4148 0.03

q5 512-KSA910YBU 0.12
q4 512-KSC2310YBU 0.12
q6 512-KSA940TU_Q 0.54
q8 512-KSA940TU_Q 0.54
q3 512-KSC2073TU 0.54
q7 512-KSC2073TU 0.54
q9 512-KSC2073TU 0.54

q10 512-LM7808CT 0.26


rough total at posting time: 14.59

q1 & q2 are 2sk34 jfets (50v) set up as constant current sources. either 2 current regulator diodes can be used at about 100v max for ~2.00 each
or
2sk30a-y jfets from ampslab.com.(20 for $20 at last check)

I have a few too.

Click to expand...

So, after toiling over both the SX-D7000 and SX-3900 schematics, I have a more complete list. There are a few holes in it however, being the following mainly:

Capacitors
AGC-004 103Z 150v Replacement P/N? (Is this a 10,000 pF 150v cap?) If so, I found 75-125LS10-R (Vishay 250v) at Mouser...
CEA331M 25L C22 330µF 25v Replacement P/N? (I found 647-UPW1H331MPD 50v (Is this correct?)
"101" Is this a 100 pF cap? What is the voltage? I found P/N 75-WKP101MCPEF0KR 440v. Is this correct or appropriate?

Transistors/Diodes
2SC1915 Q7 KSC1845 (is this the correct P/N? What is the Mouser P/N?)
2SA905 Q8 KSA910 or KSA992 (is this the correct P/N? What is the Mouser P/N?)

Also, this transistor is listed as 2SD313P on the SX-D7000 schematic and listed as 2SD313 (Q9, Q11) on the SX-3900 schematic. Is it the same? Will Mouser P/N of 512-KSC2073TU work here?

Mark, can you please look at my list (Word Doc attachment) and tell me what I have right or wrong thus far. I have gone completely cross-eyed at this point! The formatting does not display correctly on the forum if I copy/paste it. Also, my Word Doc has some notes on it that will assist me at my low-level of electronics knowledge, so disregard them please.

Thanks a million.

EDIT: I edited the Word Doc (10-30-08 at 8:42pm Pacific Time) and highlighted key areas and filled in additional P/N data that I found. Not sure if it is correct. Please verify for me before I order the parts from Mouser. Thanks.

:yes:
Hey Mark, Don't mean to bug and I know it is a lot, but were you able to give my parts list a lookover and see if I have all the bases covered correctly?

Thanks so much!

SolutionRoom said:

:yes:
Hey Mark, Don't mean to bug and I know it is a lot, but were you able to give my parts list a lookover and see if I have all the bases covered correctly?

Thanks so much!

Click to expand...

Sorry - been busier than a 9 tailed cat in a room full of rocking chairs - building code mandated construction project complete with contractors and ( idiotic or picky? ) engineering code inspectors failing the inspections because they haven't bothered to READ the prints. Couple that with year old medical bills that have suddenly reared their supposedly paid heads and dealing with TWO separate bureaucracies (public and private) that want to just pass the buck as to WHO dropped the ball rather than resolve the bills.

Couple that with being dead tired, and it makes it risky for me to accurately evaluate large amounts of intricate data until I have gotten some good rest. Maybe tomorrow, definitely on or before sunday night. But that may slip because bright and early Monday morning (after a time change no less) I have ANOTHER inspection scheduled, so I HAVE to get enough sleep to peel my tired carcass out of bed to BE there for the inspection - the inspector WON'T even ring the doorbell (he didn't the LAST time - when he was EARLY), he'll just drive away. I wanna do a dick cheney on him.......

markthefixer said:

Sorry - been busier than a 9 tailed cat in a room full of rocking chairs - building code mandated construction project complete with contractors and ( idiotic or picky? ) engineering code inspectors failing the inspections because they haven't bothered to READ the prints. Couple that with year old medical bills that have suddenly reared their supposedly paid heads and dealing with TWO separate bureaucracies (public and private) that want to just pass the buck as to WHO dropped the ball rather than resolve the bills.

Couple that with being dead tired, and it makes it risky for me to accurately evaluate large amounts of intricate data until I have gotten some good rest. Maybe tomorrow, definitely on or before sunday night. But that may slip because bright and early Monday morning (after a time change no less) I have ANOTHER inspection scheduled, so I HAVE to get enough sleep to peel my tired carcass out of bed to BE there for the inspection - the inspector WON'T even ring the doorbell (he didn't the LAST time - when he was EARLY), he'll just drive away. I wanna do a dick cheney on him.......

Click to expand...

Wow. Sounds like a mess indeed. I am sure it will all work out. I am sure that if the inspector cannot even ring a doorbell, that a cell phone call is DEFINITELY out of the question huh! Gotta love it.

Yes, good clear rested eyes and brains is a necessity for this for sure. I wanna make sure that the list is accurate and complete before dropping the Mouser order. I just got the SA-9100 in the mail today. Boy does it look like a mess. Case all busted and dirty as hell. Miraculously, every function on it works though and it sounds nice. On first inspection, it appears that the boards have been untouched as far as component work. I tried all I/O and everything works. It will be a cinch to work on as compared to this SX-3900. It will take a back seat until I get this 3900 all purring smoothly and looking slick.

So do what you have to do Mark. I apologize for pressuring on it. Just biting at the bit to get this running. I got a new baby coming on Nov 11th, so wanted to get some of the parts inside it before then... Cause I will be bleary-eyed myself for a while after the new addition arrives! You can bet on that. Thanks!

Oh, and while you're at it... Are the Sanken SC2921 and SA1215 transistors a good replacement for the outputs?

SolutionRoom said:

<snip>

Oh, and while you're at it... Are the Sanken SC2921 and SA1215 transistors a good replacement for the outputs?

Click to expand...

Yes, but it'll run you 60 bucks for 4 sets at a REPUTABLE supplier (ampslab.com), so I might not be quite as quick to condemn the originals. The danger of counterfeits is high, and the lower the price, the greater the danger.

IF you do replace all the outputs, remove them carefully and SAVE the mica insulators, that outline for insulators is very hard to find.

B&D Enterprises has them for about $39 for the entire set of 8. Are they reputable, with a small risk for counterfeits? I will, per your suggestion, wait to see if the originals are still good. Would this affect the sound in any way by replacing them? Better, worse, same or???

SolutionRoom said:

B&D Enterprises has them for about $39 for the entire set of 8. Are they reputable, with a small risk for counterfeits? I will, per your suggestion, wait to see if the originals are still good. Would this affect the sound in any way by replacing them? Better, worse, same or???

Click to expand...

Let's let the comments on B&D trickle in.

In most cases, the original transistors are left in.

The power supply is the exception.

EDIT: (12-15-2008) They trickled in, EchoWars no less says they're ok.

Thanks Mark. I will keep the originals in if possible. Did a search on AK and Google for B&D and found nothing relating to their rep, either good or bad. But based off of your comment, you must have some not so good info about them, so I will obtain elsewhere if need be. Thanks again...

At least you will get an extra hour of sleep (or work) tonight, whichever is the case!