Pioneer SX-950 Restoration Project

[musicSteve]

musicSteve, I never did buy the kit and have not worked on the unit. I've had a lot of other projects to work on. Like I stated before, I would rather save the time and headache and buy a complete kit, but yes there are a lot of problems with that too. Getting what you need versus what the kit contains and in most kits the filter caps are not part of the deal. Which if you want really good ones, it's your money and the moon is the limit. I did purchase a kit for a Pioneer Spec1 rebuild and it did not go as well as planned. I sat down and ordered all the caps and a few other parts for a Pioneer Tuner but that took a lot of time.

I bought 2-kit almost the same Pioneer cassette players he sent out 1/2 the parts and one of them and had a incomplete BOM. I had to PM him every week until he send me the parts but it took 2 1/2 months. I received most of the parts. lol never received a complete Bom for one of them and the other one had 2-amp boards and only sent me one (needed 4 total) and each kit also had missing parts or the wrong ones so the 2 units have identical boards and they had different capacitors for the same boards.
I recap one of them not thinking to much about the parts but later finding all the problems w the Bom
I need to change some of the Upw 10uf to UKL and I need to double check everything. The cassette recapping is a big job but it sounds Amazing. might start a thread to double check some of the caps being used. He also said to use the 22uf BP cap which were located all over in place and ever in the Power supply (he said he got a deal on them. I never did use them) I just used my UPW cap instead.

I think the next kit I buy is going to be for the sx-1250. The kits I'm looking at is the most expanses one but has the 4 filter caps which are hard to find and are a direct replacement.
like you said if done right will save a lot of time and this kit has all the parts.

 

[PioneerPro]

To properly order the Pioneer SX-950 rebuild parts you will need to create a Bill Of Materials (BOM) list to upload to the Mouser Website.
The Mouser part number has to be in column A and the quantity needs to be in Column B in an XL Spreadsheet. Column A can only have the Mouser Part Number in it.
I just got done creating a BOM list on Mouser yesterday and had about 6 part numbers that I needed to fix because the old part numbers were no longer available.
This does not include the Filter Capacitors or the resistor that Timothy Flath indicated that you need to replace in the beginning of this Thread. Using my list will definitely make it easier on you it took me a few tries to get all the bugs ironed out. Hopefully I have made no mistakes in my BOM list below. You should be able to copy and paste in on the Mouser website. Please let me know if I made any mistakes and I will correct them.

BOM List: Pioneer SX 950 Quantity
80-ESH225M050AC3KA 10
140-REA4R7M1JBK-0511P 4
667-ECE-A1HKA3R3I 2
647-UKL1J4R7MDD 4
80-ESH107M010AC3AA 4
598-106SVF025M 4
667-EEU-FM1C331BJ 4
EEU-FM1H101B 2
647-UES1A101MPM 2
667-EEU-FM1V221 4
667-EEU-FM1V330 2
667-EEU-FC1V470 2
80-F612JF224J063A 4
598-SLP681M100A1P3 2
647-LLS1H222MELZ 1
80-ESY337M010AG3AA 2
80-ESS475M035AB2AA 1
647-UHD1H101MPD 1
647-UPW1V101MPD 1
661-ELXV101ELL101MK2 1
647-UPW1V102MHD1TO 1
647-UPW1C221MPD1TD 1
661-EKYB101E471MLN3S 1
667-EEU-FM1E470 2
647-UPW1J470MPD 1
647-UDB1H470MHM 1
863-MJE15032G 3
863-MJE15033G 1
512-KSA992FBU 8
512-KSC1845FTA 8
512-KSC2383YTA 6
512-KSA1013YBU 2
512-KSC2690AYS 2
652-3386H-1-101LF 2
652-3296P-1-103LF 2

​

 

[PioneerPro]

I am not sure if my previous post from yesterday of the Current Mouser BOM includes the Tuner Board or not?

 

[PioneerPro]

My Pioneer SX-950 restoration is almost complete. I am waiting on a couple of Capacitors on backorder and I am having just one issue.

My problem is this one new Output Transistor on the Power Supply Board is getting overly hot in a short period of time. This only happens when the receiver is on FM mode and it heats to 142 degrees in just 1 minute. The 3 other new Output Transistors on this board are just fine. Anyone have any idea?

The two Capacitors with Red Marker on top have not been changed and are on backorder.

 

[PioneerPro]

My full restore/rebuild on this Pioneer SX 950 is done now. All the caps and most of the transistors have been replaced. I took voltage readings on the 15 pins in the Power Supply board and they are all very good and very close to what's recommended.

I turned the receiver on, Selected FM and turned the volume up to 4 on the dial and let it go for five minutes. I turned on the Mute so I would not blow my ears out and it sounded great. The only thing I am noticing that is concerning is one of the output transistors gets a little too hot. Once again this is after 5 minutes on that transistor hit 162 degrees. See photos below.

Is this normal?

Thank You

 

[Timothy Flath]

A temperature of 162°F on a single Pioneer SX-950 output transistor after only 5 minutes is too hot, indicating a likely issue with bias current, DC offset, or a faulty component in that channel. Immediately check for excessive bias current, verify DC offset, and check for cold solder joints or defective transistors/diodes in the affected circuit.

Troubleshooting Steps for High Heat:

• Check/Set Bias Current:A high bias current causes excessive heat. Ensure the bias is set according to the service manual, generally around my across the emitter resistors which is crucial after replacing transistors.
• Verify DC Offset:High DC offset on one channel will lead to overheating. It should be as close to as possible.
• Inspect Output Transistors: Remove the hot transistor and test it for damage. Ensure new transistors are correctly matched for gain (hFE) and that they are securely mounted to the heatsink with proper thermal grease/insulators.
• Check Driver Board Components: The transistors that drive the outputs might be faulty, causing the output transistor to stay partially on.
• Solder Joints: Re-check all solder joints, especially around the new transistors, for "cold" or weak connections that can cause issues.

If the voltage readings on the power supply board are stable, the issue is likely isolated to the driver or output stage of that specific amplifier channel.

 

[EastPoint]

Those aren’t outputs. That’s on the power supply board, right? Probably normal.

 

[Timothy Flath]

Those aren’t outputs. That’s on the power supply board, right? Probably normal.

I see now. I was unable to view the photos on my phone. I was just going by his verbiage.

 

[PioneerPro]

I replaced the Q10 transistor with a brand new 2SC2383, which may of been shot since I installed it backwards on my first attempt. Now after 10 minutes that same transistor number Q9 is getting to about 150 degrees and staying there. Is that still too high?

 

[PioneerPro]

I see now. I was unable to view the photos on my phone. I was just going by his verbiage.

Also curious Tim, why did you not replace any transistors in the Tuner Board?

 

[Timothy Flath]

Also curious Tim, why did you not replace any transistors in the Tuner Board?

Simple answer. I never listen to radio. Despite this, the radio works fine so I felt it best to not push my luck and risk mucking up the timer board since I do not have the skill level nor the test gear to retune and calibrate it if I change things to much by recapping and swapping out semi-conductors. To me, radio has always been lowfi. That is why my main media system in the house is based on as SA-9500 II integrated amp vs a receiver. And yes I have a TX-8500 II as a show piece that is rarely, if ever, used. It too still works fine which is a testament to these old audio components. Last reason is my SX-950 is in my basement where FM signals are marginal at best. Again, I rarely use Radio even though surprising I do get fairly good reception on the couple of stations I would actually listen to down there....