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Pioneer SX-780 question

76.189.19.19
Posted on November 6, 2009 at 16:48:13
6 Meters DX
 I have a mint condition SX-780 driving Polk Monitor 10's. I am utterly amazed at how great this receiver sounds. HDCD/XRCD/SACD on my universal player sounds stunning through this old workhorse.

Being it is probably about 30 years old, are there any maintenance issues I need to be aware of with this specific piece? Do I need to change out certain capacitors? Does anyone know what kind of output transistors these use?

Gracie!

RE: Pioneer SX-780 question, posted on November 10, 2009 at 18:05:27
lukiedog
Audiophile

Posts: 438
Location: Northern Virginia
Joined: May 27, 2005
 Here are some answers to your question:

1. The speaker relay can have issues and impede the unit from turning on or cause it to click off during operation. D712 transistor can develop cold solder joints over time, reflow these. This transistor's function is part of the circuit that supplies power to the relay. Also clean the relay contacts and inspect the vicinity for other cold joints. Some people replace the relay outright. Only do any of these if you are experiencing problems, leave alone if not.
2. Correctly set DC offset, it drifts, causing relay to shut unit down during operation.
3. Near the Darlington power packs, Q25, a power regulator transistor of some sort also experiences cold joints. Reflow. It is also possible that Darlington pack joints themselves require reflow.
4. Deoxit on all controls solves a great deal of problems.

If your unit is operating properly, do nothing except perhaps check and adjust the DC offset if it is way off.

RE: Pioneer SX-780 question, posted on November 7, 2009 at 19:15:35
Nicholas Renter
Audiophile

Posts: 446
Location: Texas, baby!!
Joined: March 18, 2002
 There are basically 2 schools of thought:

1 - If it ain't broke, don't fix it. And when it does break, only fix what broke.

2 - Go pre-emptive and replace what may be degrading (or even go for a wholesale replacement of all caps / components with a finite lifespan).

One approach is cheap in the near term (but perhaps expensive in the long term). The other one is expensive in the near term, but may not need any maintenance in the future.

There is not a "right" approach. It depends on what value you see in your piece of hardware. Personally, I'm having an SX-1250 completely restored (including new filter caps). When it's all said and done with, I'll probably have $800+ of parts and labor into this thing. But I'm gonna love it, probably hand it down to one of my kids (or ultimately gift it). To me, that's value.

If you picked up your SX-780 for $20 from CL, and you think you got a steal, then you may not want to drop the time / money into "fixing" it. However, it may completely fail tomorrow. The questions is: Do you feel lucky?

RE: Off subject, posted on November 7, 2009 at 03:53:07
Neff
 6 meters? Get a Yaesu FT-625RD for the most sensitive receiver you ever owned.

I have a 780., posted on November 6, 2009 at 18:45:11
olddude55
Audiophile

Posts: 25149
Location: Pittsburgh
Joined: July 12, 2003
 It is a sweet receiver, but there are no output transistors. The SX-780 uses Darlington-type integrated-circuit output devices. My daughter is currently using it.
The unit was rebuilt by a guy who advertises on Audiogon, goes by the handle ezekiel. He replaced nearly every cap and switching diode, upgraded the power supply caps, aligned the tuner, and replaced the standard power cord with heavy duty wire terminated with a hospital-grade three-prong plug.
That's a pretty expensive proposition, though.
If the controls are clean, if the unit powers up like it should and sounds good, just play it.
I don't know why Pioneer and other switched from output transistors to I/C output devices.
___
From the Industrial Hub of the Mid-Mon Valley!
RE: Pioneer SX-780 question, posted on November 6, 2009 at 18:40:26
Michael Samra
Dealer

Posts: 13112
Location: saginaw michigan
Joined: January 30, 2005
Contributor
  Since: June 24, 2005
 The sx780 is a nice receiver.Why not change out the caps on the boards with nichicon muses..I would change the capacitors that have exposed to heat areas and all the ones on the driver boards.
The polk 10s I have always liked..Have you thought of maybe picking up a Fisher 500c tube unit or a Sherwood S-8000IV as they both are fantastic on the Polks and ADS as well as many other speakers?
If the power supply waveform isn't pretty,neither is the sound in most cases.

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