Pioneer SX-1250 find

[Yamahaha]

Picked up a Pioneer SX-1250.

This is pretty dusty inside and I can see has had someone inside before. Makes a static "fart" when powering down. Relay kicks in fast upon power up and clicks on power down. Staic pulse follows the relay click when powering off.

Measured DV at the speaker outs. Each set A,B,C reads the same. .001v on the right and .027v on the left.

Doesn't like the turntable to be grounded. Hums until I remove the ground. Getting bleed from the AUX into the phono.

Anything sound strange here? I am decided whether this is the candidate to have redone or keep looking.

 

[wmgwizard]

Any SX 1250 that powers up and plays is worth the time and effort to make right.

Start with a thorough cleaning of all of the switches and pots. It is amazing how many issues are caused by dirty pots & switches.

 

[Watthour]

Agreed. A thorough cleaning and exercising of switches, controls, and connections would be a good step. That would include the nylon shell Amp-type power connector and output device connector pins. Markthefixer has a good tutorial for using a pencil eraser to polish the pins. The pin sockets can be cleaned chemically.

It might also be prudent to remove the channel amp boards, protection board, and the regulated power supply (stabilizer) board for cleaning, inspection, and at least refreshing the thermal grease. While it is partially disassembled it would be helpful to verify all the chassis ground connections since there is some apparent issue with grounding.

 

[Yamahaha]

Thanks but a cleaning is not exactly professional servicing. I realize I can clean it. I was hoping some who have serviced these can chime in.

 

[wmgwizard]

Just because you can do the job yourself does not lessen its value. It is a.prudent first step to eliminate the most common cause of the issues you mentioned.

If you were hoping one of the senior tech's would chime in and say "oh yeah, part xyz123 causes your issues" it isn't going to happen until you clean the unit.

I have an SX950 on the bench right now for a full refurb. I have about $225 in parts plus about 15 hours labor. If I dropped it off at a shop I expect it would cost $500-600 to do what I am doing. I imagine a 1250 would be $100-$200 more. Considering these regularly sell for $700-1200 in good condition you are still ahead of the game.

Not sure what kind of answer you are looking for, I gave you the best I could come up with after playing with this stuff for over 30 years.

 

[Tom B]

While the .027v is high for the one channel, and the .001 looks good at the speaker outputs, you would really need to look at the output connections from the Output/Driver board, before the speaker protect relay to see what is happening at power up, and power down. A scope would be best, but a dc voltmeter will work as well. Check pin 13 on each of the driver boards, and monitor what the level looks like on power up and power down. big swings of DC point to bad components, caps, or bias/dc balance settings on these output/driver boards. The 2sa750 differential amp transistors are prone to getting noisy, but usually stay noisy. I have seen issues with the 2sc869's getting noisy and causing protect circuit issues. Also had Bad (open) 2SA899 and 2SC1904's that allowed unit to come on, but caused output bias issues.
But you need to get those function controls and switches cleaned before you can begin to diagnose your phono or aux problem

 

[just dave]

Let's see some pics already!

 

[Yamahaha]

Just because you can do the job yourself does not lessen its value. It is a.prudent first step to eliminate the most common cause of the issues you mentioned.

If you were hoping one of the senior tech's would chime in and say "oh yeah, part xyz123 causes your issues" it isn't going to happen until you clean the unit.

I have an SX950 on the bench right now for a full refurb. I have about $225 in parts plus about 15 hours labor. If I dropped it off at a shop I expect it would cost $500-600 to do what I am doing. I imagine a 1250 would be $100-$200 more. Considering these regularly sell for $700-1200 in good condition you are still ahead of the game.

Not sure what kind of answer you are looking for, I gave you the best I could come up with after playing with this stuff for over 30 years.

Sorry I didn't mean to come off with attitude. What I meant to communicate was perhaps someone could give me an idea if the symptoms were more serious in nature. I clean my own gear and it does solve problems. But anything with so much power of this age is absolutely in need of caps and serious work somewhere in its many stages. Many people deoxit and call it serviced. Not saying that's you.

 

[Watthour]

That may be the conventional thought process, but not ALL the caps will require replacement. I picked up a DOA 1250 about a year ago and found the root problem fairly quickly. The FIX required removing the boards (as listed above), cleaning pins, rebuilding the regulator assembly, and setting the offset/idle. The eventual finish of the repair involved the audio/tone amp boards and tweaking up the tuner.

Your unit is working, apparently didn't fry any pre-driver or regulator transistors nor burn up any outputs or high wattage resistors, and likely only has a grounding/connection issue. Once you clean the boards, a close inspection and measurements may reveal stressed components. For minimal cost you can recap the regulator board, L and R channel audio amp boards, and the protection board. I'd avoid doing anything to the RF boards except cleaning and checking alignment but only AFTER the regulated power supplies are properly adjusted. If you WANT to clean up the audio path the equalizer amp, filter amp, tone amp, flat amp, and control amp can have their caps and suspect transistors replaced. There are qualified parts lists for all those sections posted all over this forum. If you choose to go all-out you can rebuild the power supply and replace the main filter caps ($$$) if it makes you feel more secure.

Still, my WAG is that your initial problem will be affected by cleaning and checking connections.