Pioneer SX 737

[STUKINDA70S]

I am having a service problem with a Pioneer SX 737. I am fixing this for a friend. The unit goes in to protection when the volume is at 9-10 oclock, This occurs weather there a source going through it or not. When the unit goes into protection, there is no DC at the emitter resistors. I have basically recapped the entire amp board,protection board and power supply board. I have also swapped out all the problem transistors on the same boards. I even replaced the protection relay. All the voltages at the power supply board are perfect. The same goes for the amp and protection board. Pins 5,6,7 & 8, coming from the amp board, when tested when the receiver goes into protection also have no DC at those pins, but yet still goes into protection. Very puzzling! I removed the 4 wires from pins 5,6,7 & 8 0n the protection, receiver plays clear with no issues. There is no DC on those 4 wires coming off the amp board while the unit is playing. Does anybody have any ideas what I might be overlooking. Also the voltages are adjusted and the bias is set, thanks Danny(Yesterdaysaudio)

Hey Mark I posted this in the wrong place, I am following your advice and started a new thread. I've been on Audiokarma for many years but this is the first time I ever reached out to anybody. you responded back to me in a private post, I will check and advise and get back to you thank you so much Mark.

 

[markthefixer]

This went out by PM: (easier to just copy and paste it.... multiple purposes served)

I'm gonna chalk this up to lurker being unaware of the etiquette, or an unaccustomed mistake in posting.( thus sending a private message versus a forum post.)
I can't do private help, I do PILES of public help.

usually I just send a slightly sarcastic boilerplate complaining about my horrendous PM traffic and how things get lost in the rush so please start your very own thread.

I WILL respond on the forum, and you seem to have hit significant milestones.
Removing wires from protect pins 5,6,7,8 really narrowed the problem.

Attaboy's freely given. And that's an ATTABOY...

Of course the major protection players are C1 & C2, being Sanyo solid aluminum leaky abominations, the other is of course Q1 & Q2.
It's possible these weren't recognized as electrolytic capacitors, due to 0.22 uF capacitance. Make them film caps and never have that to think about again

For me, problematic transistors are actually ALL old silicon on the power supply and protect boards. They get a new "deck" of silicon.
volume dependent, over-current protect being triggered has mostly been the Sanyo caps, but the transistors can be leaky too. Look at their legs - if blackened, that's a creeping problem, probably INTO the epoxy case....

q1- q4 ksc1845, q5 ksa992, q6 ksc2383, q7 ksc2690, D8 1n4004 etc, pin 9 to pin 10 snubber 1n4004 too


LOOKING FORWARD to continuing this in the Pioneer Audio forum.

mark

 

[STUKINDA70S]

Hey Mark, all the problem transistors on the amp board,power supply board and the protection board have been changed as per your recommendation. Also all the same boards have been recapped. As i stated in a previous post,with the wires removed from pins 5,6,7 & 8,of the protection board, receiver will play loud and clear for hours. Nothing gets overly warm, and the voltage coming from those 4 disconnected wires is as follows 0.064/0.107/0.115/0.083. these voltages were measured with the receiver playing at 10 o clock.Reconnect any of these wires with a jumper wire without touching the volume, receiver goes right into protection.All the voltages at the power supply,amp board are correct. You mentioned adding a diode between pins 9 & 10.I did that with no effect. One thing i have noticed when it goes into protection there is some sort of sound coming from the relay.I hope this is gonna post to the forum Mark, Thanks Danny(Yesterdaysaudio)

 

[bzenic]

if everything works without PB I would double check all the transistors pins and polarity of e caps on the PB.

 

[markthefixer]

You mentioned adding a diode between pins 9 & 10.I did that with no effect. Danny(Yesterdaysaudio)

You won't see any effect...

The diode is a flyback diode, protecting the relay drive transistor over the long run. All the more expensive models have one.
When the relay current stops, there is about a watt of magnetic energy that converts to electrical current. If the current isn't allowed to flow, the voltage climbs higher and higher until it does flow.

as for your protect problem: are you SURE that you have the transistors installed correctly?

Protect only triggers when D5 gets pulled down.
Either the transistors are correctly connected, which isolates that protect trigger,
and it can only be pulled down by convincing a transistor to conduct.
HOWEVER, a miswiring exposes the conductor to all manner of mischief.

Reconnect any of these wires with a jumper wire without touching the volume, receiver goes right into protection

This seems to bolster that thought.

I also wouldn't expect the mis-installed transistors to survive with usable low leakage.

 

[STUKINDA70S]

Hey Mark,I double checked the transistors on the protection board, that was It!!! One of the subs for the 2SC869, I believe its KSC1845, one of the legs was in the wrong location. I have a peak Transistor checker Mark, but i guess i need glasses, my error, but thank you for making me go back in and looking at that. Like i said with the wires removed from pins 5,6,7,8 the receiver played fine.Thanks for your help Mark, I really do appreciate it.

 

[larryderouin]

Danny; You still got your parts shop, or did you close up?

 

[STUKINDA70S]

Hey Larry, i stopped with the website and repairs.Just maintain my own gear. ,Still have alot of stock, transistors. caps and stuff. Also have alot of Pioneer parts on hand. Ebay really went south, as far as linking bank accounts. and sellers basically having to eat any problems. As far as doing repairs, shipping costs went to the moon. UPS breaks almost everything, too many headaches Larry. And you know, sometime these repairs can get very time consuming.

 

[larryderouin]

Thanks. I WAS Curious.