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SX 727 crackle, hiss and pop. Help!

P

Pioneer SX 1

New Member
Ok!
So I have a 727 that has a crackle and pop in on of the channels. How can I go about trying to resolve this issue? I'd really like to overcome it!

When It turns on the power supply has a gentle hum...then a CLICK occurs and the left channel (I think) starts to crackle, and the other side does not. I have been told it sounds like a failing transistor?! When I opened it up, I noticed four large ones at the back at the left protected by fins... Could these be the likely culprits? Or should I start elsewhere?
I have not cleaned pots or switches yet, as I an finding it difficult to get to them... suggestions?

any help would be much appreciated :)

cheers.
 
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Pioneer SX 1 said:
Ok!
So I have a 727 that has a crackle and pop in on of the channels. How can I go about trying to resolve this issue? I'd really like to overcome it!

When It turns on the power supply has a gentle hum...then a CLICK occurs and the left channel (I think) starts to crackle, and the other side does not. I have been told it sounds like a failing transistor?! When I opened it up, I noticed four large ones at the back at the left protected by fins... Could these be the likely culprits? Or should I start elsewhere?
I have not cleaned pots or switches yet, as I an finding it difficult to get to them... suggestions?

any help would be much appreciated :)

cheers.
Click to expand...

The culprits will be the LITTLE transistors, they are the bosses that control the BIG ones.... Our known troublemaker transistors are not represented in here, it predates them, thus any of the old transistors could be doing it. The replacements are inexpensive, once we figure out which ones to use. Then you get talked through replacing them.
 
So is there a particular board that I should start with? by just replacing all the components?
Thanks very much for your time!
 
Along with a total recap, Check the W21-002 board (HEAD AMP) and see if the transistors are 2sc458's or 2sc871's. the 2sc458's are problematic in that they breakdown and become noisy. I've replaced the 458's in numerous units with 2sc2240's (reversed leadout) but Mark is a lot better at figuring out the best replacement transistors. Get the manual for it and STUDY IT! And ask questions on anything you don't understand. There will be a few tests along the way. Don't get ahead of yourself. Take it slow and steady. And don't work tired(ask my 1010 how I know that!). Build yourself a Dim Bulb Tester (search AK for how). And get a Digital Multimeter with a DIODE Checker, and a hfe tester(transistor checker). These two sections of the meter will get almost as much use as the voltmeter and oHmmeter parts.

Start out with recapping the power supply board 1st. Your voltage supplies need to be up to snuff when replacing with new parts on other boards.

Do one board at a time. Power supply, test, Protection board, Test, Head Amp, Test, AF Unit, Test, Main Amp, Test.

Transistors can be installed 6 ways, only one of which works. The other 5 result in smoke, and a pile of parts that don't. So triple check the leadout, on the board, the old part and the new part so they co-exist without problems.

Larry
 
I just checked the Head amp, and I found that the transistors are all the same and the code is neither of the two: C131205G. they are also mitsubishi parts. Im assuming its either a completely different replacment, or its a pattern part with a different number? pictures of the amp are too follow soon!!!!!!
 
If you can get a readable close up of the above transistors on the board, I'm curious, if they might be 2sc1312's.

All the manufacturers made line changes that didn't get into the manuals. So it's possible that this is an authorized change.

Larry
 
I have a Pioneer SX-990 with very similar problems.

The advice here is the best you'll find.

I would start by taking a lot of photos for reference to later. I use my camera for everything to stay straightened out, and these photos come in handy to post here on AK to show others generous enough to help others.

I hope you figure this out. I'll be watching/ helping you where ever I can.

Peace,

Jim
:music::music:
 
DSC01305.jpg
Head amp
DSC01306.jpg
bottom of the board at the rear ( near the fins hahah) the soldering here has gone a bit discoloured
DSC01307.jpg
Bottom of the amp
DSC01308.jpg

DSC01309.jpg
More burning
DSC01310.jpg
THis is the transitor that is in question, Cant find any info on it!!!
 
Pioneer SX 1 said:
I just checked the Head amp, and I found that the transistors are all the same and the code is neither of the two: C131205G. they are also mitsubishi parts. Im assuming its either a completely different replacment, or its a pattern part with a different number? pictures of the amp are too follow soon!!!!!!
Click to expand...

the last zero is probably an O (as in orange) and refers to HFE range. The 5G would be a production date code, and the type is 2sc1312. Unless you are getting a lot of noise in phono, I wouldn't worry about the head amps, except for maybe changing electrolytics. If problem isn't changed by volume setting, you should be concentrating on the amplifier channel. Best to get problem remedied before recapping. Good luck.
 
Concur with sregor. 2sc1312. The "burning" on the board/wiring is from a previous attempt at repair.

Lets go thru the whole thing again, to localize the problem. yes or no to each question and which side.
1.) Does the "crackle, hiss, pop"(hereafter referred to as "RICE KRISPIES") occur in ALL functions? ie: Phono,FM, AM, AUX, etc.
2.) Are the Rice Krispies independent of the volume control?
3.) One channel or BOTH Channels?
4.) do they go away after a few minutes or there constantly?

Answer these and we can dig a little more. This will help in getting down to one board. Like sregor said unless you are getting a lot of noise in phono, it's probably down stream. This is why the questions are important. Different functions insert in the amplifier chain at different points.

Larry
2.) Is
 
The 2sc1312 can (and I emphasize CAN) be replaced by the ksc1845. BUT... there are exceptions.

I DID a cap list for the 727, but transistor replacements is a whole nuther project, that I will not get to any faster by any attempts to use unvetted transistors.

The 2sa572 is not a known troublemaker. it can probably be replaced by the ksa992.

between those two transistor numbers you can probably do the phono amp and the af unit as well as the differential input for the power amp.

but I have NOT checked these circuits for exceptions. might NOT be any - but you never know until you check.
 
Hello everyone! Exciting new developments that are annoying!
ok in answer to your questions Larry:
1) Yes, the Rice Crispies are in all functions
2) Yes, they are present with no or full volume, makes no difference
3) The crackle is only in ONE channel (right)
4) This is the wierd part. On the first test of the amp a few months ago, it had no rice crispies when I turned it on...I found after about 20 mins use, it started to Krispy and it got realy bad and I turned it off. It did this the next time I tried it.
I have just connected it all up again and its all the opposite. The Krispies came along as expected, and after 5-7 mins, it had gone completely, CLEAR AS ANYTHING! I turned it off, and back on a few times, all with no krispies. I then left it off for about 40 mins and turned it on. Krispies back, but took about 1 min to go, ive had it on for about 30 mins, and still nothing
:S very confusing!!!!!!!!!!!!!
 
Just for Sh*t's &Giggles, pull the jumpers from the PRE-OUT / Main IN RCA's. Turn on the unit. If the HISS and or the "Rice Krispies" are heard, then the problem is in the AMP.
Hook another (known good working) amp to the pre -out's and listen thru that amp. If you hear the hiss and or Rice Krispies, then the problem is in the AF UNIT.

Larry
 
Update on the situation,
Went to try it out today, massive amounts of crackle and pops in BOTH channels, the right channel was crackling away, and then the left joined in! It got so bad that the speaker relay actual cut in and shut them off, this happened multiple times too! AHHH!
 
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