Project: Pioneer SX-750

[Super Noob]

Was talking with a co-worked who has taken possession of a family member's collection of vinyl and is looking for stereo setup. Was considering offering the SX-850 that I just finished, then I spied a 'rough' SX-750 for sale. My preference is SX-850 and up... but the SX-750 that I rebuilt a couple of years ago turned out better than I thought was possible. The SX-750 is a superb unit - period. It many not have the build quality and modular feel of the bigger brethren but I really like the total value for this model - cost, size, WPC, and sound quality. The one board concept for inputs and outputs does allow for the elimination of shielded cables from the input / selection switches and outputs - which should at least in theory - improve the sound quality. In lieu of getting a crazy and spending lots of money on his first setup, I thought the SX-750 was a great candidate. Truly believe this is a great first vintage piece that should exceed expectations.

After over six hours of driving, here is what I started with:

Okay some rust going on... the side panel cabinet looks to have 'wicked' up some water and destroyed the left side panel. The previous owner said he didn't power up - was afraid.

Fired it up on DBT 60W bulb.... after some seconds - 'click'. These units never cease to amaze me. All the dial lights are out and half the indicators. FM is not working.

Let the resurrection process start. As I always say, I hope this helps or inspires others to tackle a rebuild in the future. The information shared by folks like 'Mark The Fixer", "EchoWars", "Watthour", "Avionic", "LeeStereo", plus many others - is at your finger tips for your own self education and use. The components used are based on Mark's foundation part lists with the utilization of "UPW" and "UKL" series Nichicon caps (with some film cap subs). As well, I did some modifications per some kick-ass posts by Mr. LeeStereo - Ben. Triac modification inspired by 'ksparky'.

 

[Super Noob]

The power supply caps look to be jumping out of their skin... like to start here. Always change the relays, but in this case the plating looked brand new (untypical for sure), so I elected to retain. Pretty much all caps, diodes, and transistors changed. Added a heatsink to Q12.

AWR-099 (Power Supply & Protection)
C1 Electroylic .22uf / 10v CSSA Electro .22uf 10v QYX1H224KTP Nichicon (Film) .22uf 50v
C2 Electroylic .22uf / 10v CSSA Electro .22uf 10v QYX1H224KTP Nichicon (Film) .22uf 50v
C3 Electroylic 330uf / 6v CEA Electro 330uf 6v UPW1C331MPD Nichicon 330uf 16v
C4 Electroylic 330uf / 6v CEA Electro 330uf 6v UPW1C331MPD Nichicon 330uf 16v
C5 Electroylic 3.3uf / 10v CEA Electro 3.3uf 6v MKS2C043301K00JO00 WIMA 3.3uf 63v
C6 Electroylic 220uf / 16v CEA Electro 220uf 16v UPW1V221MPD Nichicon 220uf 35v
C7 Electroylic 220uf / 16v CEA Electro 220uf 16v UPW1V221MPD Nichicon 220uf 35v
C8 Electroylic 100uf / 35v CEA Electro 100uf 35v UPW1H101MPD Nichicon 100uf 50v
C9 Electroylic 100uf / 50v CEA Electro 100uf 50v UPW1J101MPD Nichicon 100uf 63v
C10 Electroylic 100uf / 50v CEA Electro 100uf 50v UPW1H221MPD Nichicon 220uf 50v
C11 Electroylic 4.7uf / 35v CEA Electro 4.7uf 35v UPW1H4R7MDD Nichicon 4.7uf 50v
C12 Electroylic 220uf / 16v CEA Electro 220uf 16v UPW1V221MPD Nichicon 220uf 35v
C13 Electroylic 110uf / 35v CEA Electro 110uf 35v UPW1J101MPD Nichicon 100uf 63v
C15 Electroylic 100uf / 50v CEA Electro 100uf 50v UPW1H221MPD Nichicon 220uf 50v
C16 Electroylic 100uf / 50v CEA Electro 100uf 50v UPW1H221MPD Nichicon 220uf 50v
C17 Electroylic 330uf / 50v CEA Electro 330uf 50v UPW1J471MHD Nichicon 470uf 63v
C18 Electroylic 330uf / 50v CEA Electro 330uf 50v UPW1J471MHD Nichicon 470uf 63v

Slicon:
Q1 2SC869-C / KSC1845FTA
Q2 2SC869-C / KSC1845FTA
Q3 2SC945-A / KSC1845FTA
Q4 2SC945-A / KSC1845FTA
Q5 2SA823-P / KSA992FBU
Q6 2SC945-A / KSC2383YTA
Q7 2SC1384-R / KSC2690AYS
Q8 2SD313-D / KSC2073TU MJE15032G (overkill)
Q9 2SC945-Q / KSC2383YTA
Q10 2SD313-D / KSC2073TU MJE15032G (overkill)
Q11 2SC945-Q / KSC2383YTA
Q12 2SB507-D / KSA940TU MJE15033G (overkill)
D1 1S1554 / 1N4148
D2 1S1554 / 1N4148
D3 1S1554 / 1N4148
D4 1S1554 / 1N4148
D5 1S1555 / 1N4148
D6 1S1555 / 1N4148
D7 1S1555 / 1N4148
D8 1S1554 / 1N4148
D9 1S1555 / 1N4004
D10 WZ-140 / 1N5244B 14V, 1/2 Watt, Zener
D11 WZ-240 /1N5252B 24V, 1/2 Watt, Zener
D12 WZ-140 / 1N5244B 14V, 1/2 Watt, Zener

Before:

After:

 

[Super Noob]

Main filters were next, as well as the rectifier / power board that is located below the filters. This is a tight install, but I elected to use the KEMET filters (that i used on AU717 a few times). The filtering specs are good and these have soldering lugs. You will see that I added 2.2 uF bypass film caps like I typical do.

AWR-100 (Power / Rectifier Board)

Capacitors:
C1 Electroylic 470 uF / 10v CEA Electro 470 uF 10v UPW1C471MPD Nichicon (Film) 470uF 16v

Main Filter Caps:
Qty (2) Originals - Chemi-Con 15,000 uF, 50v, Electro / Kemet / ALT22A153DE063, 15,000 uF 63v

Bypass Caps:
Qty (2) 2.2uF, 450v, Polypropylene ECW-FE2W225K


Diodes
D1 1S1885 1A / 100V 833-RL202-TP 2A / 100V Diode
D2 1S1886 1A / 200V MUR220RLG 2A / 200V Ultra Fast Recovery Diode
D3 1S1886 1A / 200V MUR220RLG 2A / 200V Ultra Fast Recovery Diode
D4 1S1886 1A / 200V MUR220RLG 2A / 200V Ultra Fast Recovery Diode
D5 1S1886 1A / 200V MUR220RLG 2A / 200V Ultra Fast Recovery Diode
D6 SR3AM-8 2A / 400V STTH3R04RL 3A / 400V Ultrafast Recover
D7 SR3AM-8 2A / 400V STTH3R04RL 3A / 400V Ultrafast Recover
D8 SR3AM-8 2A / 400V STTH3R04RL 3A / 400V Ultrafast Recover
D9 SR3AM-8 2A / 400V STTH3R04RL 3A / 400V Ultrafast Recover

Before Pics:

After:
(guess I didn't grab a topside pic with filters installed - but you will see them later. They fit perfect)

 

[Super Noob]

Power Amp was next... this unit was equipped with a dual package differential pair. The offset (not adjustable on this model) was around 20mV on one channel and in the high 30mVs on the other. Those readings are commercially acceptable, but I took the time to change all the silcon on power amp, modified the driver transistor heatsinks for the new transistors, new trimmers, and re-greased outputs, cleaned the connector pins, and added a film capacitor back in (that was removed in this late production model - Oct 77).

AWH-046 (Power Amp) "B Version)
Capacitors:
C1 Electroylic 1uf / 25v CSZA Tantalum 1uf 25v ECW-FD2W105J Panasonic 1uf 450v (Polypropylene)
C2 Electroylic 1uf / 25v CSZA Tantalum 1uf 25v ECW-FD2W105J Panasonic 1uf 450v (Polypropylene)
C5 Ceramic 120p / 50v Ceramic 120pF 50v
C6 Ceramic 120p / 50v Ceramic 120pF 50v
C7 Electroylic 220uf / 6v CEA Electro 220uf 6v UES1E101MPM Nichicon (Muse) 100uf 25v (Bi-Polar)
C8 Electroylic 220uf / 6v CEA Electro 220uf 6v UES1E101MPM Nichicon (Muse) 100uf 25v (Bi-Polar)
C9 Electroylic 100uf / 35v CEA Electro 100uf 35v UPW1H221MPD Nichicon 220uf 50v (UPW)
C10 Electroylic 100uf / 35v CEA Electro 100uf 35v UPW1H221MPD Nichicon 220uf 50v (UPW)
C13 Electroylic 220uf / 6v CEA Electro 220uf 6v UPW1H4R7MDD Nichicon 220uf 16v (UPW)
C14 Electroylic 220uf / 6v CEA Electro 220uf 6v UPW1V221MPD Nichicon 220uf 16v (UPW)
Bypass 1 uF for C7 & C* missing on "B" Version (added back in) Qty 2 ECW-FD2W105J

Transistors & Diodes:
Q1 2SA798-F (Dual Package) / (2) KSA992FB (Vbe / HFE Match)
Q2 2SA798-F (Dual Package) / (2) KSA992FB (Vbe / HFE Match)
Q3 2SC1438-V / KSC2383YTA
Q4 2SC1438-V / KSC2383YTA
Q5 2SD357-C 110v, .8A, 10W, HFE 100, 35MhZ / KSC2690AYS
Q6 2SD357-C 110v, .8A, 10W, HFE 100, 35MhZ KSC2690AYS
Q7 2SB527-C 110v, .8A, 10W, HFE 100, 35MhZ KSA1220AYS
Q8 2SB527-C 110v, .8A, 10W, HFE 100, 35MhZ KSA1220AYS
D1 1S2472 / 1N4148
D2 1S2472 / 1N4148

Bias Trimmers:
VR1 Bias Trimmer 100 Ohm / 3386H-1-101LF
VR2 Bias Trimmer 100 Ohm / 3386H-1-101LF

Before & In Progress Pics:

After:

 

[Super Noob]

Triac up next... this is detailed by others previously. Bottom line it reduces arcing of the power switch contacts by changing the switch contacts just to sending over a lower power signal to the Triac gate to put the 120VAC mains in the on-state.

Looks like I missed the after picture... but as LeeStereo post directs, there is a easy place to mount on the chassis right above the switch. I applied some heat compound - no insulator needed on the Triac used here. Note = you will need a 100 ohm 1/2 watt resistor, and you should remove the snubber cap on the switch contacts.

 

[Super Noob]

Tone control board is up next... as new standard protocol, have been desoldering all pots & toggle switches for properly cleaning and polishing. This adds many / many hours to rebuild - but if you going to do something, it is worth doing it right. Push-button switches are about 10x harder and there is a fair chance to damage switch - nice that these are not applicable to the SX-750 (another benefit).

AWH-046 (Tone Control)
C1 Electroylic .47uf / 25v CSSA Electro .47uf 25v MKS2B044701K00JSSD WIMA .47uf 100v
C2 Electroylic .47uf / 25v CSSA Electro .47uf 25v MKS2B044701K00JSSD WIMA .47uf 100v
C3 Electroylic 100uf / 6v CEA Electro 100uf 6v UKA1C101MDD Nichicon (UKA) 100uf 16v
C4 Electroylic 100uf / 6v CEA Electro 100uf 6v UKA1C101MDD Nichicon (UKA) 100uf 16v
C7 Electroylic 220uf / 35v CEA Electro 220uf 35v UKA1V221MPD Nichicon (UKA) 220uf 35v
C8 Electroylic 220uf / 35v CEA Electro 220uf 35v UKA1V221MPD Nichicon (UKA) 220uf 35v
C9 Electroylic 4.7uf / 25v CEANL Electro (LL) 4.7uf 25v MKS2D034701E00JSD WIMA 4.7uf 50v
C10 Electroylic 4.7uf / 25v CEANL Electro (LL) 4.7uf 25v MKS2D034701E00JSD WIMA 4.7uf 50v

 

[Super Noob]

Next up is the FM muting and filter board. Didn't do great with pictures on this little board. Elected to keep the silicon on this board. Just caps. To remove the board, just desolder the wire wrap pins from the board side. Watch the dial string... I covered mine with some aluminum foil for additional protection pending a slip with the iron.

AWM-094 (Filters & Muting)
C1 Electroylic 2.2uf / 25v CSZA Tantalum 2.2uf 25v MKS2C042201K00JSSD WIMA 2.2uf 63v
C2 Electroylic 2.2uf / 25v CSZA Tantalum 2.2uf 25v MKS2C042201K00JSSD WIMA 2.2uf 63v
C3 Electroylic 10uf / 35v CEA Electro 10uf 35v UPWH100MDD Nichicon 10uf 50v
C5 Electroylic 100uf / 35v CEA Electro 100uf 35v UPW1h101MPD Nichicon 100uf 50v
C7 Electroylic 1.0uf / 25v CSZA Tantalum 1uf 25v MKS2C041001F00JA00 WIMA 1.0uf 63v

 

[Super Noob]

FM turner is just static.... elected to proceed with recap and disassembly of the switches. Keep in mind this board is more than a turner board, it has phono, inputs flow threw board from input selector. Did change some diodes on this board too, but for the propose of the rebuild you should just change caps. Note that this version had some changes and some of the caps had different values.

More switch cleaning... here is the deal, I use Brasso and a Q-tip and polish like my life depended on it. It takes considerable time. For the contacts moving parts, I take a piece of paper, fold it over, and gently slide the contact on the paper, then pull it up and down the folded section (slight pressure on the assembly as you slide - like holding a baby bird = not too tight not too loose). I rotate the paper crease / fold every two contacts for a fresh surface. MTF uses a sonic cleaning... if you want to know what the pros use / do.

AWE-073 (Tuner)
C27 Electro 0.47 / 50v CEA Electro .47uf 25v WIMA .47uf 100v MKS2D034701E00JI00
C41 Elecro 100uF / 16v CEA Electro 100uf 16v Nichicon (UPW) 100uf
C42 Electro 220uf / 16v CEA Electro 220uf 16v (found 100uf / 16v) Nichicon (UPW) 100uf 25v UPW1E101MED
C45 Tant 4.7uf / 16v CSZA Tantalum 4.7uf 16v WIMA 4.7uf 50v MKS2B044701K00JSSD
C46 Tant 1 uf / 25v CSZA Tantalum 1 uf 25v WIMA 1uf 63v MKS2C041001F00JA
C47 Tant 3.3 uf / 10v CSZA Tantalum 3.3uf 10v WIMA 3.3uf 63v MKSC043301K00JO00
C48 Tant .22 uf / 35v CSZA Tantalum .22uf 35v WIMA .22uf 250v MKS2F032201H00KSSD
C54 Electro 220uf / 6.3v CEA Electro 220uf 6.3v Nichicon (UPW) 220uf 16v UPW1C221MPD
C60 Electro 4.7uf / 35v CEA Electro 4.7uF 35v Nichicon (UPW) 4.7uf 50v UPW1H4R7KDD
C61 Electro 47uf / 6.3v CEA Electro 47uf 6.3v Nichicon (UPW) 47uf 16v UPW1H4R7MDD
C62 Electro 220uf / 16v CEA Electro 220uf 16v (found 100uf / 16v) Nichicon (UPW) 100uf 25v UPW1E101MED
C66 Tant .1uf / 35v CSZA Tantalum .1uf 35v WIMA .1uf 63v MPK2C031001F00JSSD
C80 Electro 10uf / 16v CEA Electro 10uf 16v Nichicon (UPW) 10uf 25v UPW1E100MDD
C81 Electro 10uf / 16v CEA Electro 10uf 16v Nichicon (UPW) 10uf 25v UPW1E100MDD
C82 Tant 1 uf / 25v CSZA Tantalum 1 uf 25v (found 2.2uf / 25v Tant) WIMA 2.2uf 63v MKSC042201K00JSSD
C83 Tant 1 uf / 25v CSZA Tantalum 1 uf 25v (found 2.2uf / 25v Tant) WIMA 2.2uf 63v MKSC042201K00JSSD
C84 Electro 220uf / 25v CEA Electro 220uf 25v Nichicon (UPW) 220uf 35v UPW1V221MPD
C85 Electro 220uf / 25v CEA Electro 220uf 25v Nichicon (UPW) 220uf 35v UPW1V221MPD
C86 Electro 4.7uf / 16v CEANL(NP) Electo LL 4.7uf 16v WIMA 4.7uf 50v MKS2B044701K00JSSD
C88 Elecro 100uF / 6v CEA Electro 100uf 6.3v Nichicon (UPW) 100uf 25v UPW1E101MED
C89 Elecro 100uF / 6v CEA Electro 100uf 6.3v Nichicon (UPW) 100uf 25v UPW1E101MED
C98 Tant 2.2 uf / 25v CSZA Tantalum 2.2uf 25v WIMA 2.2uf 63v MKSC042201K00JSSD
C99 Tant 2.2 uf / 25v CSZA Tantalum 2.2uf 25v WIMA 2.2uf 63v MKSC042201K00JSSD
C102 Electro 2.2 uf / 25v CSZA Tantalum 2.2uf 25v (found 2.2uf / 50v LL Electro) WIMA 2.2uf 63v MKSC042201K00JSSD
C105 Electro 2.2 uf / 25v CSZA Tantalum 2.2uf 25v (found .1uf / 35v Tant) WIMA .1uf 63v MPK2C031001F00JSSD
C106 Electo 220uf / 35v CEA Electro 220uf 35v Nichicon (UPW) 220uf 50v UPW1H221MPD
C110 Elecro 10uF / 16v CEA Electro 10uf 16v Nichicon (UPW) 10uf 25v UPW1E100MDD

Some Pics (focus on switch cleaning):

 

[Super Noob]

FM was just static.... measured voltage didn't look correct on the ICs, but I just kept searching for bad silicon or resistors. From watching xraytonyb on this set, I was thinking I had a similar problem as he did with some FM ceramic filters. Eventually my hard head decided to put a wire antenna on, and I was able faintly pick up a station or two. Turns out that is all I needed. I was able to do a poor man's alignment and was able to get the signals improved on the upper end and lower end, and did the final alignment. Honestly, it turned out amazingly good and is spot on. Keep in mind this turner was not working, so what did I have to lose = nothing. It works great now. Maybe someday I will get the necessary equipment for adjusting turners to spec. If you mark your original positions, your risk is reduced. Keep in mind T6 for centering of the scale is a very touchy. Reminder - non metallic tweakers.

 

[Super Noob]

Lets rattle can that transformer top / bell cover...

The wood case would be hard to replicate - it has some setbacks and would be a pain for me... maybe it was 'karma but there was a local ebay non-working / cheap SX-650 with a salvageable case. The SX-650 utilizes same case and face place. It utilizes those lovely STK packs = time to sacrifice for the better unit.

Here is the new case with some mahogany veneer...

Full LEDs... bright white + sliver = amazing looks. Yea - I know you older folks prefer yellow illumination = that is fine, but not for me.

 

[Super Noob]

Final Shots

Components:
20 Transistors
27 Diodes (including Zeners)
69 Capacitors (52 Electros / 15 Tantalum / 2 Ceramics)

Starting Point:

Where we finished:

This unit is getting shipped off to Texas soon... another save on a classic from the golden era. The fifty series delivers again = sounds clear / punchy / & proud.

 

[Lowetlx]

Looks great. Did you veneer the blocks on the face plate or cut them out of mahogany?

 

[Super Noob]

Looks great. Did you veneer the blocks on the face plate or cut them out of mahogany?

Just applied veneer to the front / outside / top faces... the case and front trims are original with applied veneer.

 

[Tripqzon]

Looks Amazing!

 

[fromnowon]

Thanks for taking the time to document and for the great pictures! I really appreciate the work and the detailed documentation in this thread. It's a roadmap for anyone restoring one of these.

There is now such a "body of knowledge" in various threads that you can search and find an amazing amount of info on a given model. This combines it into an end-to-end story. Makes me want to try to find a great deal on an SX-750.

I'll bet your coworker really appreciates it.

 

[Super Noob]

The SX-750 in my opinion is one of best overall value receiver in the 50 line up.

Thanks for the kind words.

 

[Tripqzon]

I have to agree. I just love my SX-750. I purchased it used for cheap because it was stuck in protection mode. Turned out to be a bad zener and resistor in the protection circuit itself. I haven't done a complete refurb on it yet but this receiver sounds amazing.

If you don't mind I would like to post a picture here of the veneer job I did on mine.

 

[Super Noob]

If you don't mind I would like to post a picture here of the veneer job I did on mine.

This is a community and extending a thread with other ideas is always fine by me. Share away.

 

[Tripqzon]

Thanks Super Noob.

I didn't document my refurb like you did but I wanted to share some photos of what it looked like when I received it and what it looks like now. As you will see there is a container full of capacitors that got replaced as well. I replaced the vinyl veneer with real wood veneer and stained it with a walnut stain. Hope you enjoy the photos.

https://photos.app.goo.gl/8R9esYkhVpyai45B6

 

[Super Noob]

Sweet rig... nice transformation. Looker for sure. I did red oak veneer on my 1st 750 rebuilt.

https://audiokarma.org/forums/index.php?threads/project-pioneer-sx-750.823530/