Pioneer sx-1050 restoration project

[zebulon1]

Make a print of the PS board.
Print out the rebuild list.

Thread 'SX-1050 Full Rebuild Parts List - Completed Project'

Aug 10, 2020

(EDIT: 9/12/2020 - Rebuild completed successfully and the following list has been updated to reflect all components replaced, and mouser replacement parts i used).

I just acquired a mint SX-1050 from the original owner at a great price - the kind of deal on local CL that rarely ever happens anymore. After a DeOxit/FaderLube treatment and bias/idle adjustment, the unit functions perfectly. But having rebuilt a few pioneer receivers, I know how much better they can sound after a re-cap/re-transistor treatment, and so am going to refurbish this one. I'd like to verify the main list and a...

• Wyatt Weeks
• sx-1050 recap list
• Replies: 47
• Forum: Pioneer Audio

• 

Cross check with the lists and print of the SM board illustration.
The PS is very accessible. Careful with the plastic standoffs, A small drop of Fader 5 on the plastic keepers lets the board slip past after you squeeze the retainers.. Loosen and remove all the wires harness from keepers on the bottom chassis. Have the receiver on its transformer side with the Amp heatsink and outputs removed. I push the amp board back through the chassis slot and work on it from the bottom. Use pipe cleaners or rubber bands to support the loose boards. You now should have a ton of room to access the PS.
The key is to have the receiver on its side, transformer down on the bench top.
I suggest to buy a cheap de-soldering tool for the job. Even the cheap ones are better than using braid or a solder sucker. You and the receiver will be the better. It makes the job very enjoyable. I use the Hakko FR301 (I actually have two, one as backup). At $300 its not cheap but it makes the work easy and professional looking.

 

[rdbolin]

I got it all back together. Dc offset on both side at 0.0v
Idle current on the left is 48.1mv
Right side is 50.1mv
But I have a issue on the protection board I cannot find. Wile on dbt when I turn the power on dbt goes bright then goes out. When the protection relay engages dbt comes on real dim. Only bulb i have is a 150w inconsistent.
With all speeker switches off if I slowly turn the volume knob up once it gets to about 75% ( no load ) it trips protection. Any ideas what im missing ?

 

[zebulon1]

Do not operate it on the DBT.
It sounds like it’s working.
Once the bulb goes dim it all thats needed. No shorts. Remove the set from the DBT and go to line voltage.
One thing to remember, is to reset the idle trimmers back to zero and make the final adjustments on line power.
If you set the idles on the DBT, they will be extremely high on full line power.
Copy?

 

[rdbolin]

Do not operate it on the DBT.
It sounds like it’s working.
Once the bulb goes dim it all thats needed. No shorts. Remove the set from the DBT and go to line voltage.
One thing to remember, is to reset the idle trimmers back to zero and make the final adjustments on line power.
If you set the idles on the DBT, they will be extremely high on full line power.
Copy?

Now you got me worried to put it on line power with it set the way it is..before I take it off dbt. Should I turn the idle to 0 by way of meter then turn it where it needs to be on line power. ?

 

[rdbolin]

Now you got me worried to put it on line power with it set the way it is..before I take it off dbt. Should I turn the idle to 0 by way of meter then turn it where it needs to be on line power. ?

No sir that didn't work. Took it to 0mv left and right took it off dbt set both sides at 48mv.
Still tripping protection at 50% on volume with no load.
.

 

[rdbolin]

If i go to 18 it goes into protection.
Have not connected any speekers to it yet.. lol I have no cheap ones.

 

[rdbolin]

This is the only board that would make it do this right ? If it was any other wouldn't it blow fuses ?
This is the protection board. The amp relay is working fine.
Clicks a sec after power on the the protection relay. And it stays out of protection until almost 50% on volume ( no load ).

 

[rdbolin]

Output transistors are warm to the touch ( not hot )

 

[rdbolin]

This resistor gets to hot to touch. Its the only one getting hot.

 

[rdbolin]

This resistor gets to hot to touch. Its the only one getting hot.

 

[rdbolin]

And its cracking.

 

[zebulon1]

It might be a backwards transistor in the tone amp circuit. The volume control is at the end of the flat amp circuit and before the tone amp.
If you have another pre-amp you could use that to check the main amp?
Or another amp and run the 1050 pre through it?
Edit:
Second thought don’t do the pre or amp thing. Not a great idea.
Does it go into protection with the defeat switch off?
Using a 1khz tone at a input, use a scope, looking for a voltage spike at the pre out jumpers. You even determine the channel. You could even do that with your meter set to AC volts.
Double check all your work in the tone and main amp. Most likely in the tone amp. A wrong or backwards transistor.

 

[rdbolin]

It might be a backwards transistor in the tone amp circuit. The volume control is at the end of the flat amp circuit and before the tone amp.
If you have another pre-amp you could use that to check the main amp?
Or another amp and run the 1050 pre through it?
Edit:
Second thought don’t do the pre or amp thing. Not a great idea.
Does it go into protection with the defeat switch off?
Using a 1khz tone at a input, use a scope, looking for a voltage spike at the pre out jumpers. You even determine the channel. You could even do that with your meter set to AC volts.
Double check all your work in the tone and main amp. Most likely in the tone amp. A wrong or backwards transistor.

I only worked on the protection board and the amp board. And changed 3 caps on the main power supply..
I've reached my capability. Im gonna put the hood on this one.. ive got 1100 invested in it. And I know is something simple.
There's a shop 4 hours from me. And before i really mess somthing up this unit is worth me taking it there. When I get to this frustrating level it's time to do something different.

 

[raycarr00]

I'd check the resistors for drifting on the serviced boards and for solder bridges. dc offset.

 

[rdbolin]

I'd check the resistors for drifting on the serviced boards and for solder bridges. dc offset.

Lol. Yep did all that. I dont think it would take much investigation. To find it.. but I really have gotten to frustrated to mess with it.. ive just quit smoking and my agitation level goes way up. And its just best me not do it.
And I want the tuner adjusted and at its peak performance. And the adjustments needed i dont have the skills or equipment.
But at least the tech won't have much to do.. it got a very good deep cleaning. Pots, switches, and buttons,. There's only one mark on it..
So im just gonna let a professional finish it up.
I'll come back and let yall know what he finds.
Thanks guys for your help and suggestions.

 

[rdbolin]

Well the tech is really backed up and gonna be a wile. Sovi opened it back up and for some reason have a whole different track than before.
I have no light on dbt. And power relay activates the protection relay does not.. ive lost power some how. Pin 12 on the protection board awm 090 has 0.11v and should be 60v
And connects to pin 17 on the power supply .. and thats where im lost.
When I powered it on. I Hurd a audible pop. In the area of the power supply.. I have a feeling one of the cut bits from installed parts touched somthing.

 

[rdbolin]

Ok I have narrowed it down pin #2 has the correct voltage.
Pin #17 the pin that feeds the protection board has 0v. So one of the transistors has went kaput. And they're all new. So ive done touched something somewhere i should have. Witch one should I pull first.. I have the old ones. They was good.

 

[rdbolin]

Ok I have narrowed it down pin #2 has the correct voltage.
Pin #17 the pin that feeds the protection board has 0v. So one of the transistors has went kaput. And they're all new. So ive done touched something somewhere i should have. Witch one should I pull first.. I have the old ones. They was good.

Found it these got put in backwards.

 

[rdbolin]

ok got it powered up and that issue resolved.
But there is still a issue. Idle current both sides set at 43mv off dbt
Both sides DC offset at 0v
Still something going on on the protection board. One of the resistors is getting hot and gets hotter as volume is increased. Around 5% of volume it trips protection. Turn it down one click and it comes out of protection and the resistor starts heating up agian.

 

[rdbolin]

After some more reading of Ben's kit instructions. It called for two transistors to be faced the opposite way.. well some how they only got turned quarter way around.. I had more from a previous kit.. and put them in the correct way... doesn't go into protection no more and all adjustments re- adjustmented off dbt.
Now if I can figure out what is heating up the 2.4k resistor. I dont know if its critical or not because I know some resistors are supose to heat up.. but I dont think this is one of them.
Back to the grind.