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Project: Pioneer SX-850

Thats SX-850 restoration is nothing short of impressive, love the attention to detail as well. I have an SX-850 in my collection which had a light restore in the crucial areas of where these go wrong but still mostly original and performs really well. But as all the old silicon and capacitors age even further eventually most units will need to be fully overhauled in this manner.;)
 
Super Noob said:
Tone Amp (AWH-039)
Capacitors:
C13 2.2 uF 25v Electro (CSZA - LL) / 2.2 uF 63v MKS2C042201K00JO WIMA
C14 2.2 uF 25v Electro (CSZA - LL) / 2.2 uF 63v MKS2C042201K00JO WIMA
C15 2.2 uF 25v Electro (CSZA - LL) / 2.2 uF 63v MKS2C042201K00JO WIMA
C16 2.2 uF 25v Electro (CSZA - LL) / 2.2 uF 63v MKS2C042201K00JO WIMA
C19 100 uF 10v Electro (CEANL - LL) / 100 uF 16v UKL1C101KPDANA Nichicon
C20 100 uF 10v Electro (CEANL - LL) /100 uF 16v UKL1C101KPDANA Nichicon
C21 47 uF 35\v Electro (CEANL - LL) / 47 uF 35v UPW1V470MED Nichicon
C22 47 uF 35\v Electro (CEANL - LL) / 47 uF 35v UPW1V470MED Nichicon
C23 2.2 uF 25v Electro (CSZA - LL) / 2.2 uF 63v MKS2C042201K00JO WIMA
C24 2.2 uF 25v Electro (CSZA - LL) / 2.2 uF 63v MKS2C042201K00JO WIMA
C25 0.22 uF 35v Electro (CSZA - LL) / 0.22 uF 100v MKS2D032201C00KI00 WIMA
C26 0.22 uF 35v Electro (CSZA - LL) / 0.22 uF 100v MKS2D032201C00KI00 WIMA
C29 10 uF 25v Electro (CEANL - LL) / Factory Jumper
C30 10 uF 25v Electro (CEANL - LL) / Factory Jumper

Transistors:
Q1 / 2SC1312 / KSC1845FTA
Q2 / 2SC1312 / KSC1845FTA

ACtC-3fooHTJGHhJjgZlcNLmOlGzml_MhbLiscGiQXngHNgz8n6rIH9tZQvSc8vcqe6XX6c4cDftVfMtmNufvRvhByGvJ-qFIx5WMWooY6uYx8VFCwEE4V5_0UlSmAftNmrF9RI5ugCJNAZdjzEV0r46_k8q=w377-h390-no


ACtC-3cwBGVrpW9z5kBka8m40Gk7-TKePwRFcopy0rOmmN4iQWzntbEYu1Ecnfb3dAZ3rGIwRURnQKyPNSm33aT-jmUQ1hToC6i63j3SDlYOdhPwx-HK0fswjvDFnP7zljJ5DKvQZNNZFAMyvamapzEYHSRH=w944-h366-no


ACtC-3edYQ6fyxpon3v0Qd5-t2vN3MTUlOTdCAaiErlLIydrLEJXKQsPAGhxxUpdSrcyjuR07gAoU6RbzNarhlo9cMNra5MmhHNUzrwQ-_rHwvLWvza6RSq3jf4Zd1TkV_20sXcXe740LOzCGYO9ycic0EbS=w845-h544-no


While you are in there... clean the pots and switches with D5 / flush after with F5. As well - service those push buttons switches mounted above this board.

Before:
ACtC-3cUMVchvzHiL2Bk0SuSoVcARDdlQXZ4tdfFffhMsUhPhfy6neAQAJh8N9iC6oTtbrFQ7MVt7oKS8tZMXbUWwe8r5sH6F4JG8kQVP5xyTYdA5PNH9jFnVzCOp6MXip44OlKBqw2UGBOzToIwvlFqS0i_=w685-h913-no


ACtC-3ffpbSGPfc81xFEXlMsDhUBE_vm5na9vUz3H8Jnz-zqryxWSS3ZXvEOUt_bpzh7fh6NogAzyap1aRiM8XSITXZNK1IV-vXe9AVBGBw1Iu07yLSnuY8gX38vEHmhhKhn6N0VKmC5sn6rz880W3Gc97Bk=w685-h913-no


ACtC-3c9dlDg7-W8_DrJ2N95gFSGoemn5ZhlRG_fJ7wZVx7ucjf3rCG1lehqCWxKX-Ik2RiACtpsLc_dlqNSjT9iMBZb3L8FEfjWf10WG2ze5wcaQ308jSJqw0i0oHysZ7RAxmYW3gdoNg9ZqgqGY-YNVMSt=w685-h913-no

After:
ACtC-3eZHp9ptubhYnle6cceu8WvsQx3BvBUUy5sSzBZs7rnOdODvzFipyDTjrd9HcI8FypinWYtUAdPcTimaz-p7aPpgZYbAxf2xOCpjlGcLxj2BudMfX5CCT-DDee9Rrbe8kdNjQPlDhl5z5zHXkFyTH5e=w685-h913-no


ACtC-3fmUbxTx9YCqwwgXMGLCEHc9LIxg1SorynZ3ie0fn2W2ZmmIVLngCT6YhdmCUdzdS9_rK3QqBWYkCN1Vb1UvV6v5aPnuGI2xBsOKNB3ALsEujwOYCyVZDQBrxNf-mUZ_WHyHNlHGBMt4kLccsbNIo9I=w685-h913-no


ACtC-3f3lntTPK3-SlUhDi_-Mv8oDTqEYrOjxgcgBTcmRNjhvNlq4S_1UkxJyOqKAAjLvb3wRKHsrZl46xAesN53Z-cnpiMg9oJI811S7Oc1KBAjJRJUOC-FzX_Aej5VKuu-hz20tf9S_PtGhzMyZWQC5TC6=w685-h913-no
Click to expand...
Hi. Would you kindly explain or provide a reference to changing C2-30 to a jumper versus the 10uF/25V cap? I am just finishing this board but I am stumped on that change. Thanks!
 
Depending on when the unit was made... some factory changes were implemented. My tone board had a few caps bypassed. You are safe to pop in like for like replacements if your board has additional caps where this unit had them missing / or jumpered.
 
Super Noob said:
Depending on when the unit was made... some factory changes were implemented. My tone board had a few caps bypassed. You are safe to pop in like for like replacements if your board has additional caps where this unit had them missing / or jumpered.
Click to expand...
Thanks for that info. Very interesting. I have replaced the original caps at those 2 locations.
 
Thank you for your excellent coverage of the rebuild Super Noob. Just finished a repair and refurbishment of a SX850 that recently came to Australia from Germany. it had 49V DC on the right channel output. The culprits where the matched-pair Q2 & Q4 input transistors. I built a test circuit to find and match the transistor pairs. Could you tell us how critical the matching of the transistors pairs is? Cheers Lincoln
 
Well done! I'm curious about a few things. First, how many hours do you have into just the electronics overhaul? Did you manage all of this without unwrapping any of the wire-wrapped connections?
I have one on my bench right now; I doubt the customer will want a complete overhaul but it would be nice to ballpark a number. I plan to shotgun all the 2SA726s; are there any other transistors I should summarily shotgun?
 
Hi Clark, I spent over 30 hours fault finding and researching on a SX850, charged the customer $300 plus parts. This was for replacement caps and transistors on the power amplifier and power protection boards, caps only on the power Supply. Customer just wanted it working so I kept replacing bits until it did. A few days ago, the customer called and said the phono input was cutting out after 10 minutes. So I charged another $100 to replace the caps and transistors on the phono board. Customer was happy, it sounded great. It will probably come back for more cap replacement but the customer didn’t get hit with one big bill so he’s okay with that. Hope that helps..cheers
 
Most don’t go all the way…. It’s my hobby so I can do work like this. Results are amazing. I bet I have 60 hours on this rig…. It is gone. Sold at a price of a non restored unit to my buddy’s fiend - I true act of good will.

I don’t undo wire wraps…. Tuner board requires about 5 wire wraps pins to be desoldered from the board for required access. This is correct way - don’t undo wire wraps.
 
Super Noob said:
Most don’t go all the way…. It’s my hobby so I can do work like this. Results are amazing. I bet I have 60 hours on this rig…. It is gone. Sold at a price of a non restored unit to my buddy’s fiend - I true act of good will.

I don’t undo wire wraps…. Tuner board requires about 5 wire wraps pins to be desoldered from the board for required access. This is correct way - don’t undo wire wraps.
Click to expand...

That's what I was hoping you'd say. Not the 60 hours... wow. The only wire wrap tool I have is much too small; it's the one I used back in the day for wiring computer memory boards and such.
 
Clark Leach said:
Well done! I'm curious about a few things. First, how many hours do you have into just the electronics overhaul? Did you manage all of this without unwrapping any of the wire-wrapped connections?
I have one on my bench right now; I doubt the customer will want a complete overhaul but it would be nice to ballpark a number. I plan to shotgun all the 2SA726s; are there any other transistors I should summarily shotgun?
Click to expand...

This thread:
https://audiokarma.org/forums/index...ilure-prone-whatever-and-replacements.731653/

Sx-850
2sa725 & 2sc1313 in phono amp (ksa992, ksc1845)
2sa725 in flat amp (ksa992)
2sc1312 (less likely) tone amp (ksc1845)
2sa726 & 2sc1451 - power amp - sometimes there are nice numbers on the schematic, but the BOM lists the junk as alternates. (ksa992, ksc3503) and... there it is!!!
The 2sc1451 is the bad boy, both halves of the push pull turn on hard at the same time. Smoke, flames, sparks ensue, lotsa rebuilding.
the trimpot for idle current is just as bad. Open that diode circuit up and ..... blooie..... so a dirty pot slip ring can really hurt.
protect: Q6 2sc945 S.O.A. is marginal discharging that 100uF cap. also the Q7 relay driver gets REAL tired. Use a diode snubber at the relay coil (ksc2383, ksc2690)
When Q6 goes, ALL protect functions but power on time delay are LOST!!! The only clue is a small power off thump.

power supply just gets baked and tired. I do the diodes and transistors just as a matter of course.

While throughput is not my bread and butter, I am rather sensitive to callbacks.

The "lists" started out decades ago as my work product the first time I worked on a new-to-me model.
Later on, years later it was easy to grab a copy of the parts list(s) and post them. And thus the beast was born.

Callbacks? just one in all these decades, a SX-1980 with a tuner gear that wouldn't get down to 88 mHz FM or below. A one tooth mesh mistake. Missed on alignment (blush).
 
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markthefixer said:
This thread:
https://audiokarma.org/forums/index...ilure-prone-whatever-and-replacements.731653/

2sa726 & 2sc1451 - power amp - sometimes there are nice numbers on the schematic, but the BOM lists the junk as alternates. (ksa992, ksc3503) and... there it is!!!
The 2sc1451 is the bad boy, both halves of the push pull turn on hard at the same time. Smoke, flames, sparks ensue, lotsa rebuilding.
the trimpot for idle current is just as bad. Open that diode circuit up and ..... blooie..... so a dirty pot slip ring can really hurt.
Click to expand...

I'm not finding any 2SC1451s on the schematic or BOM... and could you elaborate on the trim-pot?
 
The strangest things have happened, so we visually check for that confounded esso bee. It does have a unique appearance.

upload_2021-8-10_23-2-56.png

A trim pot has a slider on the resistance element that is moved to an appropriate resistance.

There is a moving element (the slider) to stationary element (the external pot connections) that is a pair of contacts.
sometimes this is a moving slider on a concentric ring of copper.
If that copper is corroded, the circuit could go "open", "infinite ohms" or just plain not connected.

That's BAD. Makes a lot of work, when someone was barely up for adjusting idle current,
to instead get smoke and flames that require some major rebuilding efforts.
 
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My friend/customer wants a complete rebuild. Oh boy... I'm sorting through your lists trying to put together a shopping list and noticed something that made me wonder. In some cases you replaced the 2SC869 and 2SC945 with KSC1845 and other times with the KSC2383. Could you explain?
So far, I've found lots of parts out of stock or obsolete... this is going to be harder than I had hoped.
 
The transistor positions and the functions they are expected to perform dictate the replacement.

You WILL notice that I specify the BOARD number and PART number for each one...

But that does not necessarily indicate that I am the author of the list. Once published, they became an out of control maelstrom done by well meaning authors. My original lists also haven't aged well, forcing changes. They were my personal work product when encountering a new model.

The ksc2383 (for one example) is used in the protect circuit rather than a c945.
The c945 is expected to discharge a 100 uF capacitor through a 22 ohm resistor.
The Safe Operating Area for the die was marginal (instantaneous heat in the die)
so a much more tolerant, higher current and lower Vcesat ksc2383 was specified.
Day to day the c945 worked, but decade to decade, it couldn't be counted on.
Plus it was a silent failure, normal power shutdown and ALL protects were disabled
and the only clue is a slight pop on power down.

Obsolete - certain cap lines were discontinued :( and transistor numbers are
always having their suffixes mixed (gain codes,bulk / tape etc).

I empathize, I just redid an old sx-737 phono amp list ( it's a small list ) and not ONE original part number worked or was in stock, which is what motivated me to revise it, for today's available inventory.

Search the forum, the parts values are common, so searching on the full part number for any RECENT posts
might yield substitute numbers. 1uF and 100uF are particular pita's....
 
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Some films in the signal path have not turned as great as I would like.... know that I shoe horned that polypropylene (due to my desire for this to be polypropylene).

Any LL electro or quality film should be fine including polyester. (YMMV)
 
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