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SX-434 Volume knob static

K

kyruxmacist

New Member
EDIT: Just discovered the post about cleaning with DeoxIT, will try that first. Apologies to the moderators for any inconvenience.

Hello, this is my first post here and I'm glad to have discovered the fine folks at AudioKarma. I've seen slightly similar threads, but nothing with my direct issue, so do forgive this new thread if this has been addressed before.

I just purchased a Pioneer SX-434 and set of Realistic Nova 8bs in decent shape. Hooked it all and was ready for some great new sound but met with almost no audio. When I touched the volume knob, instant static (crackling) out of both speakers, turned it a bit back and forth and the static was so loud. I quickly disconnected the speakers hoping I haven't damaged them and hooked up a set of "junk" speakers to test (decent little guys, but if they blow, no harm no foul).

In any configuration, the volume knob can be triggered to crackle just by tapping on it, turning it most assuredly is accompanied by crackling and extreme changes in volume. It will pick up radio signal (AM) and I did get my phono to play through it as well. It'll get sound, but just tapping on the knob will cause wide ranges of change in volume, almost as if you were turning the volume up and down.

I tried various configurations of hooking the speakers up to the A and B channels, left and right (i.e. A-Left and Right; A-Right B-Left, etc) and ultimately found neither channel seems to be working great, in with the B Left not giving any sound at all while switched on the B channel, but delivering sound on the A+B channel. Spoke to the seller and he was genuinely puzzled and concerned, and claimed he had both A & B connected with no issues just days before I bought it (I was leery but otherwise find him trustworthy and honest).

I'm not certain if the volume issue and speaker connect issues are part of the same problem or separate issues.

The seller offered to help troubleshoot if I couldn't figure it out, but he's 45 minutes away and I'm not opposed to learning. My intuition says it's a simple weak connection of some sort and likely easily remidied, but I'm not sure where to start.

My general knowledge about stereo equipment is novice and my experience is pretty much that I have a closet full of vintage estate sale-purchased equipment that's previously "broken" and been stored away for the day I learn how to fix it.

Appreciate any thoughts to start.
 
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The problem you have isn't a SX-434 specific anomaly. It is endemic in all electronic equipment that use potentiometers and switches. Welcome to the club, in a sense.

The contacts inside the Volume control are dirty, hence the crackling and noise. Actually all of the controls (both rotary and push-pull) on the 434 are all susceptible to contamination so do them all. You'll need to remove the TOP and the bottom plate to access the Rotary controls. The push - pull switches can be accessed from the front after the Front panel is removed. The Service manual, here will help with identifying how. hifiengine requires registration. its free however.

When you do the POT's (Rotary), Angle the straw on the DeOxit 90*. Stick a piece of wire in the straw, warm up the straw and bend to 100* and let it cool. It will keep the angle. remove the wire after cooling. Now stick the bent end into the opening in the pot (between the housing and the board where the leads are), and squirt some DeOxit D-5 in. Not much, just a 1/2 second or so. Then exercise the pot, stop to stop 40-50 times. The squirt a shot of DeOxit Faderlube to replace most of the lubricant lost with the DeOxit D-5. Do Not USE the D-5 by itself. The D-5 removes the junk but also removes the lubricant that was in the pot or switch. Without the lubricant the pot or switch can destroy itself. Both D-5 and F-5 are available locally at Guitar Center.
 
OK, So ... that didn't go well.

I did an initial clean on the pots with Deoxit. I didn't have the Faderlube the first time, but cleaned everything, let it sit and dry for probably 40 minutes, hooked the test speakers back up and - YAY! Scratchy volume knob was cured. Sounded good, just had the AM radio tuned in to test, but thought I was in good shape.

I reconnected the Nova 8Bs and hooked up the record player for another test. Got sound, not bad, but I realized it was off, the left speaker was performing distinctly louder than the right. So, I tweaked the balance back and forth - left speaker seemed OK, a little muffled. Right speaker, with the balance fully to the right was still quiet and the left speaker was still clearly performing. I went to turn the volume up and suddenly all the sound cut out. I immediately turned the receiver off and let it sit over night.

I didn't have high hopes, but I went and got some Faderlube, pulled the unit apart again, cleaned and lubed all the pots, let sit for several hours, reconnected - still no sound. Not through A or B channels, and none through headphones (which I hadn't previously tested so I can't say they ever worked or not, but I suspect it's all related). (Also, worth to note there is a slight audible pop when the selector is turned to the B channel, though no sound - tried AM, FM, and an AUX hookup).

Here's a good time to mention that while I was running the speaker wire I tacked it down to hold in place with a few staples and in some of the tighter spots ran a couple staples through the speaker wire. Ultimately a dumb and hasty move that was a little ahead of where I needed to be, but there it is.

So, where I'm at is I have a receiver I just purchased, haven't used to listen to music yet, and pretty sure I broke something.

With that info, I'm open to any thoughts.

The unit cost me $70. Not insignificant to me. But my inclination at this point is to chalk it up to "lesson learned" and seek out another receiver in better shape and keep this one as a test patient of sorts to keep learning on.
 
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Take out the staples from the spkr wire and just let it sit on the floor. If you must attach it so it sit's against the wall, cable staples with plastic inserts will work fine. Otherwise leave them alone. You've probably got a dead output transistor ($2.50 or less @ mouser) or an output capacitor or both. The 434 is relatively easy to overhaul, and replace the caps, & Transistors (output's) on. And considering they aren't the sizeof beer cans (thank god) it's fairly cheap to do also.

If the 8B's sound muffled in one channel, swap them left and right, at the receiver. If the muffled sound stays with the spkr it's the spkr. If it stays on the same side it's the 434. I'm betting on the 8B. Did you clean the selector switch for the speakers and exercise it??? If not do so.
 
So, upon a closer inspection, I realized two fuses on the power board were blown. I don't know how I missed this the first couple times I looked, but alas. Replaced them and hooked up a pair of Realistic Minimus 26s I found at Salvation Army over the weekend ($5!) and low-n-behold everything was working and sounding great. While the receiver was down I did a second deep cleaning on all the pots and switches and was very pleased. Now I have a good barometer to test the 8Bs.

Unfortunately, one of the 26s lost sound in the woofer toward the end of my testing ... so, over to the speaker sub I go :)

Very much appreciate the advice so far.
 
OK, so I ran all new speaker wire (no staples this time), connected the 8Bs and tested them out first with the FM, then AUX connected to my phone, then hooked up the turntable. They sounded pretty great, left and right channels were working great, no static, no clipping. I got them decently loud, about ¾ volume but didn't feel like I was pushing either them or the receiver. Really overall pretty pleased with the sound.

I listened at the loud volume for about maybe 15-20 minutes and then turned it down to about ½ way, modest level and settled in to reading through some forums here. Then out of nowhere the right speaker started cutting loud static cracks, similar sounding to before I cleaned the pots, but only the right side and turning the volume knob didn't seem to have much of an effect to make it better or worse.

I turned the receiver off, checked the fuses on the power board, all still in tact (perhaps worth noting the fuses I replaced call for 4A 125v and I put in 4A 250v as that was all that was available locally). I disconnected both speakers from the A hook ups and connected to the B hook ups, turned the receiver back on and had the same issue with the right speaker cracking.

Am I looking at an issue with the speakers or the receiver at this point?

As I mentioned before, my back up speakers are down to one but I suppose I can try hooking that up to the right and then the left and see if the issue repeats, which would tell me its the receiver, correct?

In that case, am I looking at possibly needing to replace the pots or the caps or both?

Thanks again. You guys' input has been really helpful.
 
Deoxit is good, deoxit is cool, but excuse if this has been mentioned before. some things, should NEVER be deoxited (such as sliders on high class EQs, ball bearing detent switches) and somethings should be faderlubed only (like real old pots from 40's, 50's and 60's tubers) and in most cases, once you do a real bad pot, follow up with faderlube and keep working it and do it again after a week, takes a while to get the bad chemicals out of there
 
quaddriver said:
Deoxit is good, deoxit is cool, but excuse if this has been mentioned before. some things, should NEVER be deoxited (such as sliders on high class EQs, ball bearing detent switches) and somethings should be faderlubed only (like real old pots from 40's, 50's and 60's tubers) and in most cases, once you do a real bad pot, follow up with faderlube and keep working it and do it again after a week, takes a while to get the bad chemicals out of there
Click to expand...

I did follow up with Faderlube on the pots and the switches (selector knob and the loudness, etc) that I cleaned. Let it sit over night and lubed it again. I haven't gone back in but thanks for the recommendation. Certainly wouldn't hurt.
 
Presume it's never been De-Oxited and Lubed before. Cutting down thru the gunk and environmental corrosion will take more than 1 or 2 applications. More like 5 to 8 applications over a month's time. Plus everytime you DeOxit it, the De-Oxit must be friction forced into the crap to soften it up and remove it. This is what DeOxit does best. Regular contact cleaner won't do this. The cutting out is most likely a heat related breakdown of one of the transistors in the amp or preamp. There are some of the AKBI's top ten most wanted transistors in it. The 2sa725's in the AWK-034 are usually rated as tied for #2 with it's kissing cousin 2sa726.

Here's a list of the parts I used to rehab my SX-434 3 years ago. Updated today. Not all the transistors were updated.
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=06a372cfb1
It's already a parts list so you don't have to go looking for parts. Feel free to add to it. I didn't add the Main Filter caps.

Based off this list.
Power Supply (all electrolytics and semiconductors)
C7 330 50 647-UPW1H331MPD
C8 100 50 647-UPW1H101MPD
C9 100 25 647-UPW1E101MED
C10 100 35 647-UPW1V101MPD1TD
C11 100 16 647-UPW1C101MED
C12 220 16 647-UPW1C221MPD
Q1 2SC1384R 512-KSC2690AYS
Q2 2SC945R 512-KSC945CGTA
Q3 2SD313D 512-KSC2073TU
D1-5 S1B01-02 512-UF4004
D6 WZ-140 78-1N5244B


Power Amp (SA720 and 725, output transistors, emitter resistors)
R83-6 0.5 2W 71-CA0002R5000KE14
Q10-11-12-13 2SA725g 512-KSA992FBU
Q18-19 2SA720R 512-KSA1013YBU
Q20-21 2SD313D 512-KSC2073TU
Q22-23 2SB507D 512-KSA940TU


BOM LIST
647-UPW1H331MPD
647-UPW1H101MPD
647-UPW1E101MED
647-UPW1V101MPD1TD
647-UPW1C101MED
647-UPW1C221MPD
512-KSC2690AYS | 10
512-KSC2073TU | 4
78-1N5244B | 2
512-KSA992FBU | 20
512-KSA1013YBU | 4
512-KSC2073TU | 4
71-CA0002R5000KE14 | 4
512-UF4004 | 4
512-KSA940TU | 2

The Main's were not included. Uprate them to 4700uf 50V. 661-ESMG500L472MP40S United Chemicon. $4.90ea. Need 2. Or if you want to keep the original value, but bump the voltage a little, this is ideal for the job. 647-UPM1V332MHD1AA Nichicon $2.52 ea


Cost for the parts from Mouser is about $22.00 Not including the Main's. Including the Mains about $34.00 plus shipping. Some of the transistors had extra's ordered so I could match them or use on other projects on the crapstack.

If your DVM has a hFe setting for transistors you can match the readings. The KSA992's need to be as close as possible as these affect the center voltage.(offset) . The closer the better. Getting back to the meter. Put the transistor in the correct side and leg pinouts. Let it sit for about 2 minutes to gie the transistor time to settle down. Grab the transistor and hold it for a count of ten. The reading will go up, and eventually come back down. This is thereason for the two minute warning. (Damned ump's and their Instant replay)

Get a copy of the SX-434 Service manual with the schematics. HifiEngine has it. Or go here for the schematic, brochure,etc. http://www.kallhovde.com/pioneer/Pioneer/Main scan page.html bookmark this one in case you get more PIONEER stuff.
 
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