Pioneer sx737 bad relay or something else?

DinD

New Member
My sister has an sx 737 that she wanted me to try to fix. I'm pretty sure it is the relay that is bad, but you all clearly know more about these receivers than I do, so perhaps you can verify that for me.

The symptoms: The unit powers up fine, tunes fine, all controls work, but after being on for an undetermined amount of time, the relay clicks and the sound cuts out. Everything is still on and running and the tuner is tuning, but no sound. Then it may click back on, or it may not.

I put a voltmeter across the relay, and the voltage climbs up and dips down when the relay turns off.

So my thought is either the relay itself is bad, or whatever is sending the switching signal is bad... but I'm no EE major, so I can't seem to figure out what sends the on off signal to the relay.

Any ideas as to what I might need to replace?

Thanks so much!
 
i would firstly monitor dc offset for both channels as its switching off .
if offset ok .then i would move in to power supply and check for cold solder joints .
mtf will no doubt be along soon with better info .
 
Ok, the protection goes on(drops OUT really...) for a reason - sometimes a VALID reason.

DC offset means that direct current (no sound, but HEAT) is flowing through the speaker, this must be kept low and STOPPED when it gets too high. This is the MAIN function of the protect system. There have been speaker fires, they are very rare and it takes some really stupid jerryrigging to bypass the protection and allow it to happen.

Your LUCK is that you can make voltage measurements while it is dropped out (in protect). That will clearly point to the problem.
You will need to download the service manual, (25 meg?) because it is an invaluable road map to the internals of the unit.

remember to INSULATE all but the TINIEST portion of the tip of your red dmm probe for when you (we ALL slip) slip, to avoid further damage. Plain old scotch tape works fine.

Then on the protection board AWM-025 measure and watch these pins :
pin 1 0.000v DC this is an amplifier channel output (to the speakers, before the relay cuts it off) DC offset when volume is turned to zero
pin 2 -13.0v DC a power supply voltage
pin 3 0.000v DC this is the OTHER amplifier channel output (to the speakers, before the relay cuts it off)
pin 4 a convenient ground point for the black lead of your dmm, although a bare metal chassis ground IS preferred
pin 9 this is the "bottom" of the relay coil, and is what allows current to flow to pull IN the relay, 35v when relay isn't activated, 9 volts or so when relay is pulled in
pins 10 and 11 +35v DC power for the whole shebang
pin 12 7.5v AC this is a "tap" on the lighting circuit and signals that the receiver is turned on (or off). a blown lighting fuse will shut down the sound!!

Now, IF all the INPUTS to the protection board say "things are OK", yet it refuses to work, that means there are some old and tired capacitors and transistors that need replacing. No big deal, we can tell you what to get, and where to get them. and they'll cost far less than the shipping... :dunno:
 
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Thank you so much for that in-depth reply. I haven't had the time to open the unit again and start testing, but I'll try to get to it before the weekend is out and I'll let you know what I find out.
 
Ok, sorry for the double post, but I had some time to work and started testing the unit.

All of the values you predicted on the protection circuit are right on. So I guess the problem lies somewhere down the line?
 
The protection board most likely needs some work. Like Mark said there are some capacitors and transistors that should be replaced. There are modern substitutes for the transistors. Capacitors can be sources from several large supply houses.
 
Now, IF all the INPUTS to the protection board say "things are OK", yet it refuses to work, that means there are some old and tired capacitors and transistors that need replacing. No big deal, we can tell you what to get, and where to get them. and they'll cost far less than the shipping... :dunno:

Ok, sorry for the double post, but I had some time to work and started testing the unit.

All of the values you predicted on the protection circuit are right on. So I guess the problem lies somewhere down the line?

The problem appears to lie IN the protection circuit.

there are some old and tired capacitors and transistors that need replacing.

edit - i've been working on the list but was distracted by a SHIPPING THEFT... thus someone beat me...
 
edit - i've been working on the list but was distracted by a SHIPPING THEFT... thus someone beat me...

I'm sorry, did I miss a post somewhere?

If one of you could post a list of what I'd need to replace, I'd love to get this thing working again. Thanks again for all your help!
 
the "beating" part was referring to the protection board's input readings being good (i.e. "should" be working) and the fact that HVHiFI said it first...
The list IS in progress, my cup runneth over - maybe when I get snowed in later today things will ease off for a bit.
 
Hi Guys and what a great forum you have here.
I am in the UK and have the sx-7730 which I believe is the Euro version of the sx737 (the wonders of google!). I think I have a problem with my 7730 that seems to be a common one and that is that "the unit powers on as normal but has no click from the relay and no sound output".
I have spent a lot of time over the last couple of days looking through this forum and reading many posts on this problem and think I have narrowed it down a little but would appreciate some expert advice before I go any further!

At first I thought the relay had failed and that I needed a suitable replacement but after reading MTF posts and others in this thread decided to do a few more tests and I'm glad I did!


Then on the protection board AWM-025 measure and watch these pins :
pin 1 0.000v DC this is an amplifier channel output (to the speakers, before the relay cuts it off) DC offset when volume is turned to zero
pin 2 -13.0v DC a power supply voltage
pin 3 0.000v DC this is the OTHER amplifier channel output (to the speakers, before the relay cuts it off)
pin 4 a convenient ground point for the black lead of your dmm, although a bare metal chassis ground IS preferred
pin 9 this is the "bottom" of the relay coil, and is what allows current to flow to pull IN the relay, 35v when relay isn't activated, 9 volts or so when relay is pulled in
pins 10 and 11 +35v DC power for the whole shebang
pin 12 7.5v AC this is a "tap" on the lighting circuit and signals that the receiver is turned on (or off). a blown lighting fuse will shut down the sound!!

:

My results on my AWM-025 are as follows...

pin 1 -02.5v DC
pin 2 -13.0v DC
pin 3 -32.5v DC
pin 9 36.8v DC
pins 10 + 11 36.8v DC
pin 12 7.4 AC

Would I be right in thinking that pin 3 is from the RIGHT OUT from AWH-033 and is the cause of my problem? Would this be down to a bad cap or another component on AWH-033? Are there any more tests that I can do to narrow down what has failed and will need replacing?

I do have the service manual and all the tools that I think I need to test and replace most of what I can see on the board.

Any help with this will be much appreciated.

Paul
 
Paul, welcome to AK! I would start a thread for your receiver as not to confuse messages to and from the OP of this thread.

It sounds like you may have a blown transistor on that amp leaking voltage, that is a very high value for pin 3. Pulling your outputs and testing them may be in order.
 
Hi Guys and what a great forum you have here.
I am in the UK and have the sx-7730 which I believe is the Euro version of the sx737 (the wonders of google!). I think I have a problem with my 7730 that seems to be a common one and that is that "the unit powers on as normal but has no click from the relay and no sound output".
I have spent a lot of time over the last couple of days looking through this forum and reading many posts on this problem and think I have narrowed it down a little but would appreciate some expert advice before I go any further!

At first I thought the relay had failed and that I needed a suitable replacement but after reading MTF posts and others in this thread decided to do a few more tests and I'm glad I did!




My results on my AWM-025 are as follows...

pin 1 -02.5v DC
pin 2 -13.0v DC
pin 3 -32.5v DC
pin 9 36.8v DC
pins 10 + 11 36.8v DC
pin 12 7.4 AC

Would I be right in thinking that pin 3 is from the RIGHT OUT from AWH-033 and is the cause of my problem? Would this be down to a bad cap or another component on AWH-033? Are there any more tests that I can do to narrow down what has failed and will need replacing?

I do have the service manual and all the tools that I think I need to test and replace most of what I can see on the board.

Any help with this will be much appreciated.

Paul

Paul, welcome to AK! I would start a thread for your receiver as not to confuse messages to and from the OP of this thread.

It sounds like you may have a blown transistor on that amp leaking voltage, that is a very high value for pin 3. Pulling your outputs and testing them may be in order.

CONGRATULATIONS IN GETTING AS FAR AS YOU HAVE!!!! :banana: :yes: :D


The power amp has 2sa726 and 2sc1451 transistors, either one of which can cause your problem.

The replacements (from mouser.com) are:
2sa726: 512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

2sc1451: 512-KSC3503dstu to-126 ecb 300v .1a 1.2/7w 150mhz 40-320hfe $0.28 ea

There are 6 ways to install a transistor, only one is correct, and if you don't know how to identify what goes where and how to determine (they can be different than the original) the lead arrangement of the replacement. ASK - there are NO stupid questions. OH, and do both channels, because it WILL eventually do THE SAME THING.

There are a few posts on transistor lead and symbol identification that I did, in the recent past.
 
Many thanks Mike & Mark for your very good advice. I have checked the transistors on AWH-033 and some appear to be leaking, quite a few infact! I will do a few more tests over the coming week to see what looks wrong and will start a new thread on it and hopefully get on the way to get this bird singing once again! Looks like I might have to replace ALL the transistors on this board for good measure :sigh:

Many thanks, Paul
 
Many thanks Mike & Mark for your very good advice. I have checked the transistors on AWH-033 and some appear to be leaking, quite a few infact! I will do a few more tests over the coming week to see what looks wrong and will start a new thread on it and hopefully get on the way to get this bird singing once again! Looks like I might have to replace ALL the transistors on this board for good measure :sigh:

Many thanks, Paul


AWH033 q1 2sa726 512-KSA992FBU $0.06
AWH033 q2 2sa726 512-KSA992FBU $0.06
AWH033 q3 2sa726 512-KSA992FBU $0.06
AWH033 q4 2sa726 512-KSA992FBU $0.06
AWH033 q5 2sc1451 512-KSC3503DSTU $0.29
AWH033 q6 2sc1451 512-KSC3503DSTU $0.29
AWH033 q7 2sd357 512-KSC2690AYS $0.76
AWH033 q8 2sc357 512-KSC2690AYS $0.76
AWH033 q9 2sb527 512-KSA1220AYS $0.74
AWH033 q10 2sb527 512-KSA1220AYS $0.74
AWH033 q11 2sd370 863-MJ21194G $4.07
AWH033 q12 2sd370 863-MJ21194G $4.07
AWH033 q13 2sb530 863-MJ21193G $4.07
AWH033 q14 2sb530 863-MJ21193G $4.07

With the exception of the outputs, the rest are just under four bucks worth of transistors....
 
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You don't want those 726's and 1451's in there anyways. Just remember to go over checking and adjusting bias after your done. Have you changed the electrolytic caps on the boards as well? May want to look at your power supply while the meter is warmed up as well.
 
I' ve been abit busy lately with work etc but am now just about ready to order from mouser.....

On my 7730 (euro ver of 737) I have 2x 2sd388 and 2x 2sb541 power transistors as opposed to those listed below. All the rest look the same. Would the replacements below be the correct ones that I need or do I need something different?
I have looked at the data sheets for the 388 & 541 but could not determine if MJ21194G and MJ21193G were suitable!!!

AWH033 q11 2sd370 863-MJ21194G $4.07
AWH033 q12 2sd370 863-MJ21194G $4.07
AWH033 q13 2sb530 863-MJ21193G $4.07
AWH033 q14 2sb530 863-MJ21193G $4.07

QUOTE]

Many thanks, Paul
 
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