Pioneer SX-1250 ~ Full Amplifier Section Rebuild at the Bench

In this video I turn a trashed SX-1250 parts unit into a usable jig for testing power supply, protection, and driver cards. This video documents the amplifier rebuild process from start to finish.
00:00 - Introduction
03:40 - Output Transistor & Heat Sink Removal
06:06 - Sandblasting the Heat Sinks
06:43 - Main Filter Capacitor Removal
08:41 - Main Filter Capacitor Testing (LC-102)
19:12 - Main Filter Capacitors Reinstalled & Initial Test
20:42 - Stabilizer (Power Supply) Card Rebuild & TS
31:08 - Output Transistor & Heat Sink Reinstallation
37:14 - Driver Card Rebuild & TS
46:00 - Stabilizer Card Adjustment
47:00 - Bias Adjustment
49:29 - DC Offset Adjustment
50:36 - Full Output Power and Distortion Reference Testing

[@anthonyrippo8518]

Sending cards will make life easier

[@NovaluxStereophonic]

I have done this for a couple of people since posting the video and it has worked out well.

[@rondickinson8741]

I think Rubio rebuilding the cars without having to sending unit somewhere is an awesome idea be a great service and that way we wouldn't have to worry about our units getting damaged by The Gorillaz in the shipping companies ! awesome video !

[@hydroy1]

AGREED ! I never let my units out of my sight, and shipping with the UPS/ Fed X monkeys is a big flat NO WAY IN HELL! I think them guys DRAG the boxs BEHIND the trucks ! and play football with them at each stop. TRUE ! I have even built custom wood cases with extra foam, and they still come back all boke to hell.

[@kenkai6133]

Thank you.

[@markrohman8318]

Thank you for responding to my questions, I will open up my sx 1250 and take a look at its general condition.

[@gime3steps]

Hey Ben, awesome video, rebuilding just the cards would be a great idea. I'm working on a Spec 2 unit, was admiring how nice they designed the removal of the cards on the 1250. Sure would have loved that option on the Spec 2. Enjoyed your work and learned some of your tricks . Thanks!

[@knifeswitch5973]

Very good content. I installed some new (modern) driver boards on a Sansui 2000a a while back. Met the guy through AK and think it was $90 shipped maybe? The were really nicely built, installed effortlessly and have been rock solid for the customer. I was impressed.

[@vintageaudioreview]

Really like your idea and the amount of detail you go into😄!

[@hydroy1]

Ben, I did enjoy it and learned a bunch. Question? if I pulled my cards on my SX1250 would you be able to take phone calls on correct removable & install? My longtime Pioneer tech passed away, and I am on my own now. There is nothing wrong with my unit now, but I feel a good going over everything every ten years or so is a wise investment because there not going to build anything like these monsters ever again. Dirt/ dust & hair in the switches are a big worry as well. In my opinion. My unit is about 8-3/4 out of 10 with a 10 being right out of the box new.

[@NovaluxStereophonic]

If you would like to discuss this further you can message me via my Facebook business page.

[@jefffeneis1841]

Great video. If I had not already dug into my 1250, I would make use of your service. But I was brave (foolish?) enough to dig into it myself, and now have a problem. I replaced the main filter caps, recapped the power supply, protect, stabilizer, and both amp boards. Now just one amp board gives me a problem. VR2 will stabilize at 75mV, BUT VR1 won't sit still! I'll tweak the adjustment to get it close to 0mV, but it keeps dancing around until all of a sudden the voltage will climb dramatically! It will then go into protect if I don't shut it off. I'm sure the problem is on the board since I swapped the board to the other side, and the problem came along with it. How about some advice for someone too stubborn to let a pro do it?

[@NovaluxStereophonic]

It’s hard to see without having it on the bench. I would be open to looking at just that card for you. Now that I have this test chassis you could just send in the card. PM if interested.

[@dennisfrancis1126]

Excellent video Ben! On the cards - do you also clean the plug-in pins? You didn’t show this so wasn’t sure. Might seem like overkill, but that oxidation on the pins (and the subsequent removal) does make a difference - especially with all the other great servicing you’re doing on these. Keep up the good work! Thanks.

[@NovaluxStereophonic]

I have tried tarnx and Brasso. I have settled on polishing with Brasso, cleaning, and then treating with deoxit d100 before installation.

[@dennisfrancis1126]

Try a fiber brush/pencil, ink eraser or a Dremel tool with small buffer wheel. Cheers!

[@NovaluxStereophonic]

@@dennisfrancis1126 These contacts are silver plated. I prefer to use less abrasive technics in this case.

[@ReyciclismoMTB]

Very nice and informative, I have a fisher rs 2015, that I got not working and some hack was in there. But anyway, have you ever consider or used a ultrasonic cleaner for the card or chassis cleaning.

[@NovaluxStereophonic]

I use an ultrasonic toothbrush on occasion. I have never thought about putting a card like that in an ultrasonic cleaner. It would need to be a pretty large rig. I’ll keep that in mind for future projects.

[@Askbob11]

Hello Ben. My 1250 seems to perform ok and able to bias each channel at 100mv. When attempting to check stabilizer voltage, it’s showing 0 on both pins. Any certain spot to ground or other issues?

[@NovaluxStereophonic]

You want one end of your probe on chassis ground and the other on the test point. Also check out my video on SX-1250 bias. The consensus among audio technicians is that 100mV is a misprint in the SM and far too high for this receiver.

[@paulv22]

Am I correct that the filter caps can be replaced without removing any other components? Also, how did you clean the chassis? Thanks. I think the heat sinks would look great if they were anodized a charcoal grey.

[@NovaluxStereophonic]

Yes on filter caps but it easier to pull out all the boards first to make it easier to work on. For cleaning I just pull all of the cards, the heat sinks and the caps and clean with a toothbrush and windex. On models like the Sansui 9090DB I remove the tuner chassis and power transformer and clean the whole thing in the sink.

[@paulv22]

@@NovaluxStereophonic Thanks for the reply. I have a 1250 that's been mostly restored, but the filter caps are original. I'm tempted to replace them but I'm far better on mechanical problems than electrical. I don't have the ability to test capacitors. Do you know how likely it is that the originals need replacement?

[@NovaluxStereophonic]

@@paulv22 take a look at the bottoms. If the little vents have yellow/brown crusty stuff around them they should probably be replaced. If no venting and the unit sounds good and comes out of protection fine they are probably OK to stay. If you do replace them know that you may need to drill out the original ring terminals a bit to fit the new screws. Also study the schematic a bit and take lots of before pics so that you get the polarity correct. This is a +/- supply which means one cap actually has + going to ground which can catch some people off guard the first time.

[@paulv22]

@@NovaluxStereophonic Thanks. Great info. I'll definitely verify all that before I change anything.

[@user-gd1ch8is5w]

This video is captioned "Part 1" -- was there ever a Part 2? I can't find it.

[@NovaluxStereophonic]

I always meant to do a part 2 for preamp/tuner but have not got around to it yet. Someday…

[@jefffeneis1841]

Ben, one more thing FYI... I also replaced transistors Q1, Q2 and Q11. Interesting to note that both pads for the STV-3H varistors on both amp boards had lifted on my 1250 as well. Viewers should be aware.

[@davewilliams5932]

Hey Ben, what di you use as a dummy load?.

[@NovaluxStereophonic]

A pair of 250W 8 ohm non inductive carbon resistors encased in aluminum. I am not sure of the exact part number.

[@davewilliams5932]

@@NovaluxStereophonic oh, ok thanks.

[@mikexing2605]

Great video, question if I may, what heat sink compounds do you use or recommend for the output transistors and the transistors on the regulator board that are easily available? Thanks.

[@richardadelberg8961]

I’d be very interested in sending u the boards out of mine for rebuilding of caps, diodes and noisy transistors

[@NovaluxStereophonic]

Richard. Shoot me a message on my Facebook business page and we can chat. If your amplifier is currently stable and main filters don’t look stressed your unit may be a good candidate.

[@scottskillman]

Thank you for the graphic warning. That was disgusting!

[@andylau2941]

Where are you located?

[@NovaluxStereophonic]

NYC

[@hasemkokabi6773]

this powerful man should be given to his man not you