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New Member With Technics SA-424 Problem

Traxxasislif

Traxxasislif

New Member
Hi All! I just got into the hobby of home audio. I've been into portable cassette decks and repairing them for some time now. I have a decent knowledge of electrical systems, soldering and the like, I purchased a technics sa 424 receiver and rs m222 cassette deck from a friends dad for $10, and a pair of technics sb l50 speakers. On to my problem.

When i set the whole system up, the right speakers sounded amazing, but the left sounded awful, like it was blown. I initially thought the speaker was blown, but after switching the speakers, i confirmed that they both worked. I thought that maybe there was an issue with the main speaker circuit, so I wired both speakers to the remote hookups, and the same problem occurred: poor quality from the left channel. after this, i wired both speakers to the right channel, one on the remote and one on the main, and they worked! however i didnt want to overload the right side amplifier. I took the unit apart and blew the dust off of it but could not see anything obviously wrong. If anyone has any advice or help i would greatly appreciate it!
 
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Just to eliminate the obvious, have you cleaned all the controls / switches? If not, give this thread a look:

http://www.audiokarma.org/forums/showthread.php?t=207005

Sometimes dirty controls can cause all sorts of problems, and cleaning with Deoxit is an easy fix in many cases.

Does the problem occur with any source? Try the tuner, aux, and phono input to see if the problem follows.
 
I have not cleaned the controls, and yes the problem occurs on every source. I'll try cleaning with DeOxit next. Thanks for the fast reply!
 
Hopefully, a good cleaning will fix things. If not, hifiengine.com has the service manual available for free (just need to create a free account) to download.

I had a SA-424 some years ago, and regret selling it. Sounded pretty darn good for a 45 wpc receiver.

Good luck, and welcome to Audiokarma. :thmbsp:
 
Update: I still have not had time to clean the pots and switches, but i made an observation: when I turn the unit on there a loud click of a relay about 3 seconds after turning the unit on. Is this normal?
 
Yes, the relay click is actually what you WANT to hear. It means the amp section works fine, and no components are blown. That's a promising sound. :yes:

Things could still be dirty, and if that doesn't fix the issue, I'd look at page 13 of the service manual, and check for amplifier DC offset and adjustments with a digital multi meter - according to the SM values. This thread (while VERY long) is a great help in testing:

http://www.audiokarma.org/forums/showthread.php?t=5634

If the left channel is passing a lot of DC, it could result in bad sound. If both channels measure similar (low) DC offset, then the issue is probably something else.
 
Cleaned all the pots, no change:/ I guess l'll try the DC offset
*edit* what do you mean by page 13 of the service manual? that page isnt in english:| the left channel sounds really bad, how "bad" can dc offset make it sound? could there be something simple I'm overlooking? this is my first hifi setup. Also, it sounds perfect when listening through headphones. Not sure if that has anything to do with the problem but I thought I'd mention it. Really appreciate the help and support of this forum! Hifirob2 you rock!
 
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Cleaned all the pots, no change:/
Click to expand...
How about the switches ? Deoxit (clean) the Main and Remote speaker switches.
DC offset won't really effect sound quality. Icq(bias) can effect sound quality. Page 8 "amplifier adjustment" is in english.


Try the headphone jack with a set of headphones. See if SQ is any better.
 
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I was looking at page 13 using the Adobe reader for the pdf file of the service manual. On the actual SM, it's page 8. It talks about amplifier adjustments number 1 and 2.

But....you say the sound out of the headphones is fine? No issues at all, even in stereo? That's interesting. That would mean all is well with the amp section, and the problem maybe lies in the speaker connections? The relay comes in before the headphone output, so if the headphones sound fine, then the relay is ok.

Try to measure DC offset at the speaker outputs per the link in post six, and see what numbers you get. If the numbers are within a normal range (zero to about 30mv), then I would take a closer look at the speaker selector switches. Maybe they need another cleaning. If the numbers for the left channel are out of whack, then it could be something more serious.

edit....looks like Avionic posted while I was typing.
 
If headphones sound the same as the speakers. Give the protect relay a couple taps and listen for any changes in sound quality.
 
When I took the unit apart it looked like the switches are sealed, I couldn't find any openings on the switches. As for the headphones, they sound phenomenal. No problems whatsoever. Listening through headphones makes me more eager to get sound pumping from the speakers!! This unit has the technics twist and lock connectors on the back, I cant really tell when they work or not. However, I've disconnected and reconnected the both speakers from the left and right as well as main and remote speaker connections, and still get sound issues from the left channel... kind of at a loss. I will test again to reconfirm.
 
Most likely need to disassemble the switches to clean the contacts. Post a photo of them.
Check the solder connections on the switches for ring cracks in the solder.
 
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Hmm look the circuit board over real close where the speaker jacks are soldered. A crack in that area of the printed circuit board or a bad solder connection could also be the issue.
 
checked solder joints at speaker connections, they looked okay but i went over them with my iron anyways, reassembled. no change:(

ill check the solder around the switches. I read an article about cleaning a different technics model with the sealed switches, the author of that post said to heat a paper clip and melt a hole into the switch for cleaning... does this sound right? how does a sealed switch get dirty? Will post pics when possible.
 
Aside from cleaning the pots & switches, move up or down, or push in & out the tape monitor switch. The tape monitor and tone defeat switch (if yours has one) can also cause said symptoms.

A sealed switch does not get dirty from external sources such as dust persay, but rather it gets dirty from carbon build up caused by electrical spark and/or contacts.
 
okay, I went over the solder joints on the main and remote switches, nothing changed. I've had enough for today :boring: I'll try cleaning the the sealed switches tomorrow. Thanks for all the help! Will update tomorrow. Happy Listening:music:
 
I will post a video of the problem at some point this weekend, as well as pictures of the switches. In the mean time, is there any reason to not run both speakers on the right channels? right now i have the left speaker wired to the remote connection and the right speaker on the main connection (both on the right channel). is this a bad thing? because it sounds nice right now. I really want to get it working how its supposed to be but in the mean time is this "okay" to do?
 
Personally, I would not run it with speakers hooked up to both the right channel speakers connections. This amp uses STK8040 outputs, and they don't play well when running under 8 ohms. Hooking both speakers to the right channel will put a 4 ohm load on the amp (this assumes your speakers are 8 ohms each). You could run into trouble doing that. At low volumes, maybe not such a big issue, but check the top vents for a lot of heat. If the receiver gets hot, shut it off until you resolve the issue with the left channel.

Plus, you'll only hear the right channel - it won't be true stereo.
 
cademan said:
Aside from cleaning the pots & switches, move up or down, or push in & out the tape monitor switch. The tape monitor and tone defeat switch (if yours has one) can also cause said symptoms.

A sealed switch does not get dirty from external sources such as dust persay, but rather it gets dirty from carbon build up caused by electrical spark and/or contacts.
Click to expand...

the tape monitor switch
Click to expand...
If it was the Tape Monitor the headphones wouldn't work either.
 
I can't figure out why I'm not getting sound... The headphones sound phenomenal on all inputs, the controls don't produce cracking sounds when adjusting then.. The left speaker just sounds awful
 
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