Issues with my new project: SX-737

Howdy all, from Texas! I know this is the place to come when its about Vintage gear... I picked up for $79 the sx-737 and all the lights work. When I playing some music from my LG phone>AUX, I had a lot of music-sound distortion. Tried it on the PB of Monitor 1 with same distortion, not much volume, but equal in both speakers.
Tried another idea,,, changed to Fm and Am and without an antenna, I got clear, loud sound!
Therefore I have clear decent sound-no distortion, and when I used the AUX and playback of Monitor 1, it was distorted and like in didn't have very much power. I'm asking should I be looking first at the preamp boards (2) in front, speaker relay for bad contact...needs cleaning? Where should I start?
Thank you in advance, I need a project so I'm ready to dive in.

One question is on the power amp heat sink. One transistor on the heat sink shows the paste , heat compound was leaking down? Is that a problem, or normal?? I also noticed some caps have a black dot on them, wonder why?
Is Mark out there?? I know he has seen all of this many times, Good thing He's here!. Thanks

Turn down the volume on your LG PHONE. Most likely it's volume is too high and overloading the input to the 737. Today's phones, Ipad's mp3 players can produce upwards of 2-3V which is way higher than the input sensitivity of the AUX (Which IIRC is somewhere near 1/2v.

As for the output transistors, it looks like someone had at least removed the outputs and put too much compound on the mica insulators. This is NOT NORMAL.
Remove each one,one at a time, clean the transistors, heatsink, and both sides of the mica. Then put an OPAQUE TRANSLUCENT LAYER on both sides of the mica. It's a microscopic gap filler, not an insulator. Use a Silicone based Heatsink compound. DO NOT USE ARCTIC SILVER. Radio Shack had some decent stuff, but they are now gone. So use what you can get as long as it's not metal bearing and NON-CONDUCTIVE. PIONEER originally used a CLEAR Insulating Adhesive on the output's at that time along with the mica's. It can look like there is no compound but it's there. Remove it with alcohol or acetone then use the Silicone compound.

Not sure what the black dot is for. Seen it on most of my PIONEER's. You're probably going to recap it so as long as it's working now, nothing to worry about.

Thanks for your input Larry. Before the iphone, I did play my Sony 5 disc cd player with the same results. I'm planning to take the preamp out after trying one more time to play a cd in aux. monitor 1 & 2 and see if there is any difference. What would you recommend iin starting to change out caps and transistors? I was thinking the power board first, then pre-amp board. Control and power amp boards last? I did the phono amp board 4 years ago on my sx-838. Given I haven't found the problem yet and believe the power amp appears to sound fine, as old as it is, I want to correct the problem first to remove the distortion and then move step by step to restore the 737. The unit is very clean on the inside as is the face plate and veneer.
Question, this model has a different color veneer then the 838-1010, any ideas why?

First things first, this receiver needs to have a Deoxit treatment, this could be the source of your distortion.

http://www.audiokarma.org/forums/showthread.php?t=207005

A nod to cleaning first :yes: Deoxit is your friend here.

Next, I would check those transistors on the preamp board- namely those 2SA726's which tend to cause problems as they get old. (Q1 & Q2 on the schematic)

Secondly, although they may not be causing your issue, replace those 2SC1451's on the power amp board (Q5 & Q6). They are the ones with the aluminum wrap around them, like "cans". As MTF and Larry will tell you, WHEN not IF they fail, they take out the output drivers as well as the outputs themselves:thumbsdn:

VintageMad89 said:

A nod to cleaning first :yes: Deoxit is your friend here.

Next, I would check those transistors on the preamp board- namely those 2SA726's which tend to cause problems as they get old. (Q1 & Q2 on the schematic)

Secondly, although they may not be causing your issue, replace those 2SC1451's on the power amp board (Q5 & Q6). They are the ones with the aluminum wrap around them, like "cans". As MTF and Larry will tell you, WHEN not IF they fail, they take out the output drivers as well as the outputs themselves:thumbsdn:

Click to expand...

Hey! How you doing? Same results after deoxiting the controls up front. Understood on transistors that need to be replaced. While reasembling the front controls< I had the receiver on and getting clean sound on AM and noise/hiss on FM due to no antenna. while moving the unit, I touched the antenna for AM? on back and the sound became distorted, and louder. I can see it become louder because of grounding but became static and distorted. I could manipulate the antenna to clean up the sound. I guess I have a unit that looks real good inside out,,,but a little sick, shall we say..?


Hey I need help on ordering parts like caps, transistors etc. Mouser has added more to selecting a capacitor like"
http://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/_/N-75hqt/[/IMG]

I'm at a loss which to select from MTF list.

I haven't seen even ONE voltage reading from the regulated power supply. THAT"S FIRST!!!!

No I'm NOT here (much)... severe ( :sigh: as well as expensive :tears: NOT my health - that's fine)
issues outside of AK are demanding my posting time.

markthefixer said:

I haven't seen even ONE voltage reading from the regulated power supply. THAT"S FIRST!!!!

No I'm NOT here (much)... severe ( :sigh: as well as expensive :tears: NOT my health - that's fine)
issues outside of AK are demanding my posting time.

Click to expand...

Could you walk me through with step by step?

1st. CLEAN EVERY POT, SWITCH, RCA JACK. Like Mark says if it goes in/out, up/down, or round and round it gets cleaned.

Read these threads......Idiot's Guide to DeOxit....Revisited

DOWNLOAD the manual from here get the HD version.

Compare the parts list in this thread http://www.audiokarma.org/forums/showthread.php?t=457663 with your unit. There can be undocumented changes in your unit. Once you finish, cut and paste it here with your changes, and one of us will vet it for use.

DO NOT ORDER anything until the list is vetted. Keeps your cost down via shipping.

Read the thread on BJT's http://www.audiokarma.org/forums/showthread.php?t=43186

Start by taking voltages of ALL PINS on the POWER SUPPLY BOARD

This is the Format
POWER SUPPLY BOARD XXX-000 (board #)
Pin 1......+ or -(Polarity) xx.x (voltage with Decimals) vAC or vDC (type of voltage.

GND is Ground. Usually to the Chassis at clean shiny area. BLACK METER PROBE to chassis. Red Meter Probe gets TAPED, HEATSHRINK TUBING, etc. to all except the extreme tip of the probe. Prevents "AW SH**'s, andfurther damage to the unit.

DO NOT UNWRAP or REMOVE WIREWRAP FROM PINS on the board. All of the 737 boards can be moved to work on by loosening the tiewraps, and tiedowns to gain slack in the wiring. If you MUST remove the board, unsolder the pin with the wire from the board, tape and number it.

There is a thread by MARTY Socal with Rehab threads for most PIONEER receivers. http://www.audiokarma.org/forums/showthread.php?t=457663 The 737 is included. Get the lists and consolidate it. Then compare it with your unit, board by board.

The BIGGEST PROBLEM with rehabbing gear is the owner and their overwhelming desire to get it running yesterday. 1. It ain't gonna happen overnight, no matter how many leprechaun's you catch. 2. 90% of us work, or have Honey do's that take up time. We don't sit on the computer 24/7. IT's gonna take time. No barley or grain beverages while working on the gear. There are Dangerous VOLTAGES inside, so keep one hand in your back pocket while working on it. You don't want the 737 defibrillating you!!!! 1.) it hurts like hell, and 2.) it's 99% FATAL!

SLOW DOWN, count to 10000 by 1/2's, take a few deep breaths, and relax. The more relaxed you are, the better off the 737 will be. Rushing leads to mistakes and injuries (none of which we want to see or hear about).

So read up on the threads, and we'll get you started.

definitely what he said ...^^^^^^^^^

larryderouin said:

1st. CLEAN EVERY POT, SWITCH, RCA JACK. Like Mark says if it goes in/out, up/down, or round and round it gets cleaned.

Read these threads......Idiot's Guide to DeOxit....Revisited

DOWNLOAD the manual from here get the HD version.

Compare the parts list in this thread with your unit. There can be undocumented changes. Once you finish, cut and paste it here with your changes, and one of us will vet it for use.

DO NOT ORDER anything until the list is vetted. Keeps your cost down via shipping.

Read the thread on BJT's http://www.audiokarma.org/forums/showthread.php?t=43186

Start by taking voltages of ALL PINS on the POWER SUPPLY BOARD

This is the Format
POWER SUPPLY BOARD XXX-000 (board #)
Pin 1......+ or -(Polarity) xx.x (voltage with Decimals) vAC or vDC (type of voltage.

GND is Ground. Usually to the Chassis at clean shiny area. BLACK METER PROBE to chassis. Red Meter Probe gets TAPED, HEATSHRINK TUBING, etc. to all except the extreme tip of the probe. Prevents "AW SH**'s, andfurther damage to the unit.

DO NOT UNWRAP or REMOVE WIREWRAP FROM PINS on the board. All of the 737 boards can be moved to work on by loosening the tiewraps, and tiedowns to gain slack in the wiring. If you MUST remove the board, unsolder the pin with the wire from the board, tape and number it.

There is a thread by MARTY Socal with Rehab threads for most PIONEER receivers. http://www.audiokarma.org/forums/showthread.php?t=457663 The 737 is included. Get the lists and consolidate it. Then compare it with your unit, board by board.

The BIGGEST PROBLEM with rehabbing gear is the owner and their overwhelming desire to get it running yesterday. 1. It ain't gonna happen overnight, no matter how many leprechaun's you catch. 2. 90% of us work, or have Honey do's that take up time. We don't sit on the computer 24/7. IT's gonna take time. No barley or grain beverages while working on the gear. There are Dangerous VOLTAGES inside, so keep one hand in your back pocket while working on it. You don't want the 737 defibrillating you!!!! 1.) it hurts like hell, and 2.) it's 99% FATAL!

SLOW DOWN, count to 10000 by 1/2's, take a few deep breaths, and relax. The more relaxed you are, the better off the 737 will be. Rushing leads to mistakes and injuries (none of which we want to see or hear about).

So read up on the threads, and we'll get you started.

Click to expand...

WILL GET VOLtAGES TOMORROW. I"m taking all advice and planned on taking my time, because I want to understand what I'm doing and knowing why I'm doing that. I'm great on computers, build mega systems in the day. now I want to try this.:thmbsp:

These are the voltages from the Power Supply board--AWR-057.
21 pins. Where its blank -no readings.

1.
2.
3.-00.3
4.-00.2
5.
6.
7.-37.4
8.
9. 35.8
10.-35.5
11.
12. 13.5
14. 34.5
15. 30.1
16. 30.1
17. 22.6
18.
19. 12.8
20. 12.8
21. 12.8


What do you see with the numbers?

Go back with the Service Manual's schematic in hand and determine which pins are grounds (1.), and then after you've tested those for continuity, check the rest that are blank for AC VOLTAGE. In other words Pins 1 thru4, 6, 8 and 11 are AC. Pins 5 and 18 are Grounds. Look at the drawing. Everything coming off the transformer is AC. To get DC it has to go thru a Rectifier.

To prevent any confusion in future voltage lists the following format should be used:

Board number to get everyone on the same sheet of music:
BOARD NUMBER (AWR-057)

Identify each pin by number, then the POLARITY of the Voltage (+ or -), the voltage, and the type of voltage (AC or DC)

AWR-057
1.....\ AC VOLTAGE What is it???
2...../ " " " " " "

3.....-00.3 (NO GOOD as these are the DC riding on AC Voltage)
4.... -00.2 ( " " " " " " " " " " " " "

5.....what is reading in oHms?? Bad grounds can do funny things!

6...........AC VOLTAGE What is it????

7.....-37.4 .....This voltage OK. Add Ac/DC[/b]

8.................... AC VOLTAGE What is it

9. 35.8 (ok) Add polarity and AC/DC
10.-35.5 (ok) Add Polarity and AC/DC

11................... AC VOLTAGE.

12. 13.5............WRONG! Should be Negative Voltage. Where is pin 13???

14. 34.5 \
15. 30.1 \
16. 30.1 / numbers are ok, but polarity and AC/DC missing
17. 22.6 /

18.....what is reading in oHms?? Bad grounds can do funny things!

19. 12.8 \
20. 12.8 | Same as 14 thru 17.
21. 12.8 /

Your help is only going to be as good (at minimum) as the information that you gather and disseminate. If you're old enough you may remember this..... G.I.G.O. or GARBAGE IN - GARBAGE OUT. So put as much info in as you possibly can, even if you think it may not be relevant.


Generally the numbers are a little low but within tolerance. A rebuild of the Power supply with upgraded /heavy duty parts will make it bullet-proof. But for right now, the voltages look good.


Larry

Majoryyz said:

Hey! How you doing? Same results after deoxiting the controls up front. Understood on transistors that need to be replaced. While reasembling the front controls< I had the receiver on and getting clean sound on AM and noise/hiss on FM due to no antenna. while moving the unit, I touched the antenna for AM? on back and the sound became distorted, and louder. I can see it become louder because of grounding but became static and distorted. I could manipulate the antenna to clean up the sound. I guess I have a unit that looks real good inside out,,,but a little sick, shall we say..?


Hey I need help on ordering parts like caps, transistors etc. Mouser has added more to selecting a capacitor like"
http://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/_/N-75hqt/[/IMG]

I'm at a loss which to select from MTF list.

Click to expand...

Hi from Scotland!

Larry and Mark have you fixed as far as parts lists and testing is concerned :thmbsp: Very helpful guys!

Read this thread and copy the attachment in the 1st post. Insert it in your manual. The bias and offset adjustments in the manual are wrong (backwards). The attachment shows the CORRECT instructions. http://www.audiokarma.org/forums/showthread.php?t=464083