Power up test at each stage of repair?

[Stevescivic]

I am currently working on recapping my Sx-1050. Do you folks recommend that I recap say the protection board and then a power supply board and then fire it up on the dim bulb tester at the completion of each stage to ensure that the recap and transistor replacements are working correctly? Amplifier was working perfectly prior to me starting the work. So far I have completed the caps on the Reg-a power supply board and the protection board. Transistor replacement will happen tomorrow.

BTW is there any real need to change out the resistors or diodes as some have suggested if they have zero signs of heat damage? The flame resistant resistor covers are still nice and white and when I pulled a couple from the power supply board they measured in spec still. I suspect that the previous owner was gentle on his receiver and never abused or drove them hard. I can't speak for the zener diodes but they too seem to be working just fine.

 

[blhagstrom]

Test firing after each phase is done is a great way to check work so far. Do it. If you make a mistake. You know where to look.

Zener replacement is up to you. It's an option since they are fairly stable and known issues are rare in Pioneer, MTF may have some insight into ones that may be suspect.

The flip side of not replacing them is that you are already there, they are cheap, they are active components that need to perform properly, so there really is no reason not to replace them except trace wear and tear. If your desoldering and soldering skills are excellent, then go for it.

Parts made today are light years ahead of 70s tech.

Resisters are very stable and passive so they last forever. It's an odd duck resistor that fails all by itself. I suspect a defective part. You know, 70s tech.

Other than known trouble maker transistors and the electrolytic capacitors, there are few other parts that need to be replaced on a working unit during a restore.

 

[Stevescivic]

It is a bit more involved and requires me to partially button things up before powering up each stage but I think at the minimum that I should be doing this step after recapping REG-A power supply board, protection and then the main power supply board.

I think what makes me not have full confidence in my work is when I'm doing transistor replacement. MattSD saved my unit from probably catastrophic damage when he pointed out in the BOM list I had that I had a KSD1616 transistor for the protection circuit when it should have been a KSC2383. One thing I noticed about my SX-1050's (I actually purchased another working unit for fun) that the soft start surge suppressor on mine does NOT have a electrolytic cap and the surge suppressor resistor style looks different too. I can say with confidence that it is all original Pioneer but what I don't get is why the different style and no electrolytic cap? I even found on the REG-A board that there were 2 electrolytic caps that had different voltage values than that from the factory. MattSD said that chances are it was a factory shortage of caps and they subbed in a slightly higher voltage cap. Specifically the caps were 47uF 50 volts yet the service manual calls for a 47uF 35 volt. I replaced the old original caps with the lower voltage "published factory spec" version.

I will admit that working on the SX-1050 is a dream compared to the SX-3800 I recapped years ago. So much room to work in that it's a pleasure to repair.

 

[zebulon1]

The scat tells the story for the cap voltage requirements.
The cap voltage has to be at or above the circuit voltage. The next concern is the size of the replacement cap. You want it to fit the original PCB holes and within the other surrounding components and structure.
Many times I see Pioneer use caps with three times the circuits highest voltage.
On the large filter caps, a 20% plus voltage margin is a good idea. And a modern cap with the higher rating voltage will probably fit in the original mount/clamps.
General rule is, a higher voltage rating than the circuit it resides.

 

[petehall347]

capacitors are best rated at above max voltage that it will ever see even under a fault condition such as a failed regulated voltage supply .

 

[Stevescivic]

oh definitely. I really considered upsizing the voltage on my caps but in the end my concern was deviating too much from the original specs which could adversely impact the sound (if it is in the signal path). If I bumped up voltage or capacitance too much there could also be an issue with excessive inrush (although I doubt it would be an issue for tiny little caps).

I would love to somehow jack up the power outputs of my SX-1050 to rival that of the SX-1250

 

[ConradH]

I power things up after each board is done. Otherwise, if something goes awry, it's harder to find.