sx-939 static

Clicking back and forth rapidly? In and out of protection? Without sound too? Or just with sound?

We have gone over setting the offset voltage and idle current, correct?
 
Clicking back and forth rapidly? In and out of protection? Without sound too? Or just with sound?

We have gone over setting the offset voltage and idle current, correct?

yes, clicking in and out of protection with sound and as soon as I turn it down to minimum volume it stops.

I was starting to wonder if I need to go back and set the offset voltage and idle current again. Could changing those two transistors with KSA992 cause me to have to reset the voltage and idle current?
 
yes, clicking in and out of protection with sound and as soon as I turn it down to minimum volume it stops.

I was starting to wonder if I need to go back and set the offset voltage and idle current again. Could changing those two transistors with KSA992 cause me to have to reset the voltage and idle current?


--- sigh --- most definitely yes. anytime ANY work is done on the amplifier or power supply

Did you get(extra ?) ksc1845's or ksc2310's? They would be for q1 and q2 of the protection board, sometimes as the health of the amplifiers improves, other unnoticed weaknesses assert themselves. They (q1,q2) are unusual enough that routine replacement isn't warranted. Risk of repair problems higher than risk of occurrence and all that.
 
well...I hate to speak to soon and jinx myself...but it appears to be running solid for about couple hours last night using FM, and aux cd player running through it. Still need to check the phono stage but no static and no clicking in and out. :music: thanks again Mark for all your help over the last year or so with this, I'm glad I finally got back to finishing it. But, like you say other components might fail as I get this working, and I do believe I have extras for q1 and q2 for the protect board. :thmbsp:
 
I finally got a turntable hooked up to check out the phono stage inputs...

phono1 - noticed right channel not nearly as loud, was able to unplug rca's and plug back in (right first) and it suddenly became louder and sound fine then drop off again later after listening. but sounded really good and clean, with a tad bit of buzzing coming from the left channel.

phono2 - both channels sound equally as loud in volume but after a while i got some distortion and believe it tripped the protection on for a couple seconds. I'll test again tomorrow and see if i get same results.


I imagine the phono amp needs new caps and replacement of transistors?
-actually I'm looking at the manual and unable to locate the phono amp board.
-edit: I think I located it...is it the Equalizer amp board (AWF-013-0)?

if so, I have more KSA992's to replace Q1-Q4 (2SA725's) maybe I could start there and if that doesn't cure it, order and replace Q5-Q8 (2SC1313's) and maybe all the electrolytic caps?

Not quite out of the woods yet with this one, but feeling close! :thmbsp:

UPDATE: I replaced Q1-Q4 with KSA992's and now I have no sound from the right channel, looks like I need order some 2SC1313 and lots of caps and come back at this early next week.
 
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Missing (weak) right channel only on phono inputs

so Mark...do you think I'm on the right track if the phono stage is the only problem left with a weak or missing right channel? to replace all caps, and transistors?

see previous post before this one.
 
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ksa992 is ecb with lettering facing you and leads down, then go left to right.
(the 2sa725's were BCE, and I sure hope you didn't go by the way the old transistors were facing)

After caps and transistors, there isn't much left (you did check resistors when the individual transistors were out of circuit? Since you were having problems.) electronically to go wrong - except switching at the function switches. That's more than enough - they overthought the plumbing and the works are easy to jam up.

phono 1, phono 2 and mic are switched through the function switches (phono 1 , phono 2, mic) on the input side of the phono amp (three to one select), so dirty/bad contacts can mess up the lowest level signal in the receiver.

All of those three inputs when inactive are grounded through 100 ohm resistors. Measuring from the center of the RCA plug to ground with the input off will get you a read of the resistance of the common and grounding contacts, and from the center of the RCA plug to either pin 6(L) or pin 10(R) of the phono amp will get the resistance of the common and signal contacts.

There is ONE MORE GOTCHA, and it's a nasty one.

There is feedback in the phono amp to control the gain and alter the gain / frequency response curve intentionally, in the 950 the feedback network is selected by a switch, either RIAA equalization for phono 1 and phono 2. That's TWO different switches and contacts per channel for phono as well as a third switch and contacts per channel for MIC equalization. Guess what happens with bad contacts?

So with all that switching, I'm not surprised at the symptoms.

clean clean clean those function switches!!
 
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ksa992 is ecb with lettering facing you and leads down, then go left to right.
(the 2sa725's were BCE, and I sure hope you didn't go by the way the old transistors were facing)

yes, I did install them correctly, I read some posts about it on a similiar thread of others replacing them - the ksa992 went in with the flat side facing the opposite direction.

After caps and transistors, there isn't much left (you did check resistors when the individual transistors were out of circuit? Since you were having problems.) electronically to go wrong - except switching at the function switches. That's more than enough - they overthought the plumbing and the works are easy to jam up.

I did not, kinda jumped the gun and started replacing (Q1-Q4) before I heard back from you.

phono 1, phono 2 and mic are switched through the function switches (phono 1 , phono 2, mic) on the input side of the phono amp (three to one select), so dirty/bad contacts can mess up the lowest level signal in the receiver.

I can hit these with deoxit again, believe I did in the beginning.

All of those three inputs when inactive are grounded through 100 ohm resistors. Measuring from the center of the RCA plug to ground with the input off will get you a read of the resistance of the common and grounding contacts, and from the center of the RCA plug to either pin 6(L) or pin 10(R) of the phono amp will get the resistance of the common and signal contacts.

Checking...

There is ONE MORE GOTCHA, and it's a nasty one.

There is feedback in the phono amp to control the gain and alter the gain / frequency response curve intentionally, in the 950 the feedback network is selected by a switch, either RIAA equalization for phono 1 and phono 2. That's TWO different switches and contacts per channel for phono as well as a third switch and contacts per channel for MIC equalization. Guess what happens with bad contacts?

So with all that switching, I'm not surprised at the symptoms.

clean clean clean those function switches!!

Yessir - focusing on cleaning the switches!
 
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Yessir - focusing on cleaning the switches!

Your mission is to get sub 1 ohm connections on each and every function switch position.

BUT

after 2 more tries and IF it doesn't work, we must assume problems with the deoxit technique, so either you get it, or we discuss the cleaning a bit more... The deoxit may not be making it in..
 
these are the measurements i got from the center RCA function inputs to ground and also pin 6 (L) and 10 (R) for phono1, phono2, and Aux

Ohm reading for center RCA inputs to ground for all L and R = 00.1 (is this the sub 1 ohm we want?)

Ohm reading for center RCA inputs to pin 6(L) = 100.2

Ohm reading for center RCA inputs to pin 10(R) = -1

they were all checked in the de-pressed (not active) position

I'll have the rest of the caps and transistors to finish the phono board as soon as they thaw out Texas!
 
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looks like I should have my mouser parts tonight to get the caps/trans replaced on the phono board and see if it cures my weak right channel.
 
Mark, I've now replaced all the caps and transistors on the phono board and still have the same symptom (but did get rid of the slight buzzing from left channel)...really weak sound from the right channel on phono 1 and 2...I can turn the balance all to the right and get sound plus alot of what sounds like wind noise on a mic and can see the woofer moving in and out alot.
tried switching the rca's from the turntable and still only get sound from left channel. Aux and FM sound fine, have even sound coming from both channels.

I can press the mono switch and of course get sound from both the channels.

I can go back and deoxit those switches more, but I really sprayed them good from front and backside and worked each one in and out tons.

Does my readings above tell you anything? :scratch2:

At this point, the only thing I can figure (see post #45 update) is maybe after installing Q1-Q4 - I put one in wrong? I'm going to go back and double check everything closely.
 
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I am going to have to explicitly spell out every resistance test for the feedback and output switching in the unit. Because there IS a problem there.

Only then will I be able to tell whether or not the deoxiting has taken, or if the deoxit is getting to the contacts. Sometimes one can spray and spray and it doesn't get where it's needed.

It's frankly going to take me a while to get the explicit instructions figured out, written and posted. I'm seriously swamped here.

for the next five weeks I am going to be busier than the Devil in Las Vegas.... so my time on the forums will be severely reduced. If I catch up, Then I will be on the forums a bit more often....

BUT I stole too much time from this outside issue to instead post on this forum, and now it's coming back to bite me on the a** with a vengeance. It's a deadline I have no control over, and a longstanding commitment I cannot shortchange.
 
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protect tripped after running awhile...

good news! I went back and checked the EQ (phono) board over and found a transistor (Q6) that I had the emitter and collector legs foolishly installed wrong. So all is well with the unit, right channel working now and spinning some vinyl through it and it sounds really good.

Thanks again Mark, and hope you Vegas stuff go smooth for you. :thmbsp:

EDIT: after it ran for about 20-30 min. it tripped the protection on, so there must be something not right with my voltage/idle current. I will go back and take readings again and reset if needed.
 
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OK, there are several possibilities, starting with a weak protection relay driver transistor (heat related?), through having the dreaded 2sc1451 (and 2sa726) transistor(s) in your amplifier.

I didn't want to confuse the situation earlier. I now regret not telling you to get them too, at the same time, for future need.

The bright side is, that as far as problematic transistors go, with the addition of a pair of 2sa725's in the control amp (like in the phono amp) that's all the transistors that get dicey over time. Toss in (out really) the few sky blue Sanyo caps and only age related effects of things drying out (small or cooked electrolytic caps - transistor thermal paste etc) are working against you.


2sa725,2sa726 are replaced by the ksa992's

the Q7 relay driver transistor 2sc1384:
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
(q6 a 2sc945 could be replaced by:
512-KSD1616AGBU to-92 ecb 60v 1a 0.75w 160mhz 135-400hfe $0.09
while you're in there and get a 1n4004 diode
512-1n4004 to add on across the relay coil to protect Q7 in the future)

the 2sc1451's:
512-KSC3503estu to-126 ecb 300v .1a 1.2/7w 150mhz 40-320hfe $0.28 ea

for now, just see if heating / cooling the relay driver transistor Q7 on the awm-062 board cures the protection trip if the offset voltage is ok, which it probably is, it takes quite a bit of offset to trip...
 
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protect tripped after running awhile...

OK, there are several possibilities, starting with a weak protection relay driver transistor (heat related?), through having the dreaded 2sc1451 (and 2sa726) transistor(s) in your amplifier.

I didn't want to confuse the situation earlier. I now regret not telling you to get them too, at the same time, for future need.

The bright side is, that as far as problematic transistors go, with the addition of a pair of 2sa725's in the control amp (like in the phono amp) that's all the transistors that get dicey over time. Toss in (out really) the few sky blue Sanyo caps and only age related effects of things drying out (small or cooked electrolytic caps - transistor thermal paste etc) are working against you.


2sa725,2sa726 are replaced by the ksa992's

the Q7 relay driver transistor 2sc1384:
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
(q6 a 2sc945 could be replaced by:
512-KSD1616AGBU to-92 ecb 60v 1a 0.75w 160mhz 135-400hfe $0.09
while you're in there and get a 1n4004 diode
512-1n4004 to add on across the relay coil to protect Q7 in the future)

the 2sc1451's:
512-KSC3503estu to-126 ecb 300v .1a 1.2/7w 150mhz 40-320hfe $0.28 ea

for now, just see if heating / cooling the relay driver transistor Q7 on the awm-062 board cures the protection trip if the offset voltage is ok, which it probably is, it takes quite a bit of offset to trip...


I'm a little confused with this last post from you above...

Those trouble transistors have already been replaced (except for pair on the control board)

This is my progress of components changed so far...(as of 2/10/11)


amp board (awh-030)

Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, Q12

C1, C2, C3, C4, C5, C6, C11, C12


protection board (awm-062)

Q6, Q7

C1, C2, C3, C4, C5, C6

1n4004 diode across pins 9 and 10


control amp bd (awg-027)

Q1, Q2 (I put back the orig. 2SA725's because I only had enough
left to replace the ones in the EQ board at the time.)


EQ - Phono board (AWF-013)

Q1, Q2, Q3, Q4
Q5, Q6, Q7, Q8

and all the Electrolytic caps
---------------------------------------------------

NOTE: the only two remaining 2sa725/726 are Q1 & Q2 on the ctrl board.

I am not completely sure my offset voltage/idle current is ok, I will check carefully again tonight.

Are you saying in the last sentence of your post to simply run the unit for awhile (heating up) and then turn off, let rest (cooling down) and see if it stops going into protect ? like a break-in period ?
 
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ok, borrowed yet another multimeter and this one is registering with the turn of the VR pots...

DC offset - was able to nail down 0.00mv for both L & R

Idle Current - was only able to go as high as 00.3mv and the pots wouldn't turn any further in that direction. I take it this is 30mv

Is that bad I wasn't able to reach 00.5mv or 50mv ?

DMM was set to 200v DC - and the unit was warmed up for 20 min.
 
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it ran for 2 hours sounding great with turntable hooked up!

and then...it started going in and out of protection again. :thumbsdn:

it felt awfully warm to the touch on top of vents. :scratch2:
 
Mark,

I found more ksa992s...so going back to control board and replace the last 2sa725s (q1,q2)

and recheck DC offset/idle current and see if that makes a difference since you said those get dicey over time.
 
it ran for 2 hours sounding great with turntable hooked up!

and then...it started going in and out of protection again. :thumbsdn:

it felt awfully warm to the touch on top of vents. :scratch2:

No mention made of power supply work, relay runs off of +35v, pin 5 of power supply - it could be falling down on the job. Q3 through R18 (33 ohms) drives it = watch the +35 or check it when it goes into protection.

Q3 is a itty bitty 2sc1318, a
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
may be more appropriate to the situation.

also check the -13v and the 7.5v AC to see if they is still there while it is in protection.

sorry about the mix up about what had been done and if any frustration showed through it is about non AK matters and sorry if it got loose.
 
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