View Full Version : SX-950 went into protection playing an LP


39cross
04-05-2013, 08:08 AM
Had this strange thing happen last night. We were listening to an old LP of a reading of Wind in the Willows, when suddenly the output when silent and I could hear switching going on inside the unit. Turned it off and back on, the tuner put out sound as usual. Went back to the same spot on the record and the same thing happened again - the SX-950 went into and out of protection mode, then went silent.

Turned the power switch off then back on, and moved the needle further in on the record, it played fine until the end. Switched over to FM for a while, no problems.

We've been using this receiver for several months on a daily basis. I recapped the EQ board last November, replaced the transistors then too. Never any problems until last night. Been using that phono input the whole time.

Is this a sign of an issue with the receiver? Or was there something odd about that record? Was it just a coincidence it happened in the same spot? Otherwise it played fine. I've never had that happen before.

1TUFSS
04-05-2013, 09:22 AM
Static discharge? :eek:

markthefixer
04-05-2013, 01:30 PM
did you recap the protection circuit? there are some very vulnerable caps in there too. 0.22uf iiac... Then it will become more sensitive to transients - which is indicated by repeating that section of the record and getting the same trip.

39cross
04-05-2013, 02:12 PM
Thanks Mark - I haven't done any other work on it. The phono section was unusable until it was repaired. Otherwise it is untouched.

tsd71
04-05-2013, 02:31 PM
Search the database, there are many threads just like yours, if you have a multimeter you can post power supply, & protection voltages. Here is a good thread to learn from.
Also download the service manual if you haven't done so already.

http://www.audiokarma.org/forums/showthread.php?t=351569

39cross
04-05-2013, 03:08 PM
Search the database, there are many threads just like yours, if you have a multimeter you can post power supply, & protection voltages. Here is a good thread to learn from.
Also download the service manual if you haven't done so already.

http://www.audiokarma.org/forums/showthread.php?t=351569
Thanks for the suggestions and the link. I was planning on doing a more extensive recap/rehab at some point. Looks like that time is now.

I thought it was strange that a voice recording would trip this thing on a record in good condition...it just seemed kind of flukey.

I have read many of the threads here on recapping the SX-950. I'll make use of them.

39cross
05-10-2013, 06:32 AM
An update and a question or two. I recapped the protection and power supply boards, replaced the AWM062 Q1 and Q2 2sc869's, and replaced the AWR101 Q3, Q5 and Q7 with the suggested KSC2690 and KSC2383 replacements. All seems right now, hopefully it will stay that way. As a bonus the sound quality is noticeably improved.

Question 1: The AWR101 Q3 and Q5 transistors were not 2sc1318's as on the schematic and as listed in the posts I've read. They were 2N2102's. Could these have been original, or replacements? I noticed that one of the plastic stanchions had it's top broken off. Otherwise I don't see any evidence anyone was in there before.

Question 2: I've read in some of the sx-950 posts that it's recommended to put an 1n4004 diode across pins 9 (anode) and 10 (cathode) on the AWM062 protection board. I wanted to 2x I have that right before going ahead and wrapping it up for now.

tsd71
05-10-2013, 07:50 AM
An update and a question or two. I recapped the protection and power supply boards, replaced the AWM062 Q1 and Q2 2sc869's, and replaced the AWR101 Q3, Q5 and Q7 with the suggested KSC2690 and KSC2383 replacements. All seems right now, hopefully it will stay that way. As a bonus the sound quality is noticeably improved.

Question 1: The AWR101 Q3 and Q5 transistors were not 2sc1318's as on the schematic and as listed in the posts I've read. They were 2N2102's. Could these have been original, or replacements? I noticed that one of the plastic stanchions had it's top broken off. Otherwise I don't see any evidence anyone was in there before.

Question 2: I've read in some of the sx-950 posts that it's recommended to put an 1n4004 diode across pins 9 (anode) and 10 (cathode) on the AWM062 protection board. I wanted to 2x I have that right before going ahead and wrapping it up for now.

those 2N2101's look to be replacements, MTF recommends the flyback diode on pins 9 & 10, I use this method on every 850, 950 I restore. Nice work!

EchoWars
05-10-2013, 08:16 AM
'2N' devices are rarer than hen's teeth in Japanese gear (I can only recall a few '2N' FET's being used in some Kenwood gear). That said, they were never used on the PS board.

qguy
05-10-2013, 08:46 AM
Is it possible that the portion of the track could have subsonic info ? Have you tried engaging the subsonic filter ?

39cross
05-10-2013, 12:05 PM
those 2N2101's look to be replacements, MTF recommends the flyback diode on pins 9 & 10, I use this method on every 850, 950 I restore. Nice work!

Thanks! I appreciate the confirmation. I have an 850 that could use these updates too, someday.

'2N' devices are rarer than hen's teeth in Japanese gear (I can only recall a few '2N' FET's being used in some Kenwood gear). That said, they were never used on the PS board.

Good to hear this, I wondered if it was a production run substitution. There was a long moment of cognitive dissonance when I was looking for the 2sc1318's and couldn't find them.


Is it possible that the portion of the track could have subsonic info ? Have you tried engaging the subsonic filter ?

The problem was unrepeatable the next day with the same record, but then started showing up randomly. It must have been a early warning sign. Hopefully it's all fixed now.

39cross
05-16-2013, 12:01 PM
I was looking over some of the recap lists, and I was wondering if I should reconsider the replacement I used on the power supply board, AWR-101, Q7 next time I go in there. I used a KSC2690AYS.

I was working off the list here, http://mail.audiokarma.org/forums/showthread.php?p=6612375, which listed:

AWR-101: Q7 2SC1318 +28v series pass reg
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40

But elsewhere I'm seeing:
AWR-101: Q3, Q7 2SC1318
512-KSC2383YBU to-92 ecb 160v 1a .9w 50mhz 160-320hfe $0.17

I'm not sure how much it matters, since it seems to be working fine, the 512-KSC2690AYS is used as a replacement for Q5 2SC1318, but that seems to be because it carries more of a load.

markthefixer
05-16-2013, 02:13 PM
look at the dates of my two recommendations, the 2690 is later. Also notice that the 2383 is q3 and q5, while the 2690 singles out q7 only. in that case q3 is the 2383.

the q7 substitution of just a to-92L case had always bugged me a bit.

39cross
05-16-2013, 04:40 PM
OK, thanks for confirming! That seemed to be the latest list I could find.

Just for the record, here's a picture of the transistors formerly occupying AWR-101 Q3 and Q5 as mentioned above.

http://www.audiokarma.org/forums/attachment.php?attachmentid=430620&stc=1&d=1368740496

markthefixer
05-16-2013, 06:47 PM
yeeesh..

tsd71
05-16-2013, 08:39 PM
those are definitely not original, looks like something from a Dynaco restore I just got done with