Got the Service Manual / Schematic from there already, Thats my goto with any receiver I pick up
thank uPS @mikiekimi had to update my labels on the schematic ( didnt realize it was mirrored from the image, now fixed. )
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Pioneer SX-770 : No Sound ( Troubleshooting / Repair ) Help.
- Thread starter QUiKSR20
- Start date
Got the Service Manual / Schematic from there already, Thats my goto with any receiver I pick up
thank uPS @mikiekimi had to update my labels on the schematic ( didnt realize it was mirrored from the image, now fixed. )
Had a little free time today and got to pull & test every transistor except the "Outputs" Not sure if thats necessary.
Heres what I found using my DCA55 Tool on each one :
Input 2 Side - ( side that had visible work )
Q6 - Tested BAD ( Was a replacement ECG289 that failed )
Q4 - Tested Good Gain = 113 ( Original, Has Y Label )
Q8 - Tested Good ( Was a replacement PNP Sanyo B507 9J / Gain 51 )
Q2 - Tested Good Gain = 337 ( Original, Has Mitsubishi Logo C870 46F )
R26 - Tested Bad ( no reading )
Input 1 Side - Looked OEM ( all original parts I think )
Q5 - Tested BAD - Short Circuit ( Original, Has Mitsubishi Logo C904 26D )
Q3 - Tested Good Gain = 136 ( Original, Has Y Label )
Q7 - Tested BAD I think [strange reading] - Reading common cathode, Center pin giving no reading ( Original, Has Mitsubishi Logo A569 45D )
Q1 - Tested Good Gain = 82 ( Original, Has Mitsubishi Logo C870 46F )
R25 - Read 2.2 on the ohms setting of the meter ( seems strange unless im using wrong setting ) board says 200 and testing a new 100 ohm resister reads a 100ohm resister at 99.9
I still have to pull the trimmer @ VR4 ( was mislabeled as VR3 previously by me ), So far lots of bad parts.
Heres what I found using my DCA55 Tool on each one :
Input 2 Side - ( side that had visible work )
Q6 - Tested BAD ( Was a replacement ECG289 that failed )
Q4 - Tested Good Gain = 113 ( Original, Has Y Label )
Q8 - Tested Good ( Was a replacement PNP Sanyo B507 9J / Gain 51 )
Q2 - Tested Good Gain = 337 ( Original, Has Mitsubishi Logo C870 46F )
R26 - Tested Bad ( no reading )
Input 1 Side - Looked OEM ( all original parts I think )
Q5 - Tested BAD - Short Circuit ( Original, Has Mitsubishi Logo C904 26D )
Q3 - Tested Good Gain = 136 ( Original, Has Y Label )
Q7 - Tested BAD I think [strange reading] - Reading common cathode, Center pin giving no reading ( Original, Has Mitsubishi Logo A569 45D )
Q1 - Tested Good Gain = 82 ( Original, Has Mitsubishi Logo C870 46F )
R25 - Read 2.2 on the ohms setting of the meter ( seems strange unless im using wrong setting ) board says 200 and testing a new 100 ohm resister reads a 100ohm resister at 99.9
I still have to pull the trimmer @ VR4 ( was mislabeled as VR3 previously by me ), So far lots of bad parts.
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mikiekimi
USAF Ret 1992 - 2012...Korea/OEF/OIF
It looks like it's reading 2.2 Mohms. If true, then it's way off...
With all of those other components testing bad, and the charred remains of R25/R26, you'll be best served by replacing just about everything (minus the other good resistors) on the board. I'll be curious to see what the VRs measure. If you're going to end up with a partial rebuild, I'd strongly consider replacing all the VRs. Otherwise when one goes sideways, you'll just end up with similar damage.
With all of those other components testing bad, and the charred remains of R25/R26, you'll be best served by replacing just about everything (minus the other good resistors) on the board. I'll be curious to see what the VRs measure. If you're going to end up with a partial rebuild, I'd strongly consider replacing all the VRs. Otherwise when one goes sideways, you'll just end up with similar damage.
Thats exactly what its reading, The meters on AUTO so when I scan my 100 ohm the M logo goes away and it reads a perfect 100Ω
Do you know if the 200 labeled on the schematic is 200ohm 1/2 watt? It doesnt say and I cannot read the bars that well on the part ( Ill look at other threads for a better pic maybe ).
By everything do you mean :
All Transistors ( this is getting done 100% ) ( ill use your parts list above )
All 4 VR Pots
Output transistors? ( id assume not these ) ?
Caps? Physically they all look fine so id rather skip for now if I can ( can do down the road ).
Thanks, Gotta find suitable VR's
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Jimbo40
Super Member
Well your off to a good start.
Try Newark for parts and digikey.
Some of the new transistors may be reversed pin also and the one replaced may have been reversed and put in wrong. For example 2sa869 is BCE pinout, it's replacement is a ksa992 but the pinout is ECB so it goes in reversed, center pin being the same.
You can look at the original side that still exists to make sure you get them in right.
Also with those fried resistors check the board carefully for broken traces.
You should get some kind of reading on that pot too.
That could be the whole thing that started this.
Try Newark for parts and digikey.
Some of the new transistors may be reversed pin also and the one replaced may have been reversed and put in wrong. For example 2sa869 is BCE pinout, it's replacement is a ksa992 but the pinout is ECB so it goes in reversed, center pin being the same.
You can look at the original side that still exists to make sure you get them in right.
Also with those fried resistors check the board carefully for broken traces.
You should get some kind of reading on that pot too.
That could be the whole thing that started this.
Thanks for the response @Jimbo40, I really appreciate it!
I have a decent background in audio and troubleshooting cars & computers but for vintage audio electronics repairs im a complete newbie ( reading and learning a ton as I go ).
As for the pinouts I picked up a DCA55 which makes that aspect a little fool proof ( perfect for me ) , Each replacement transistor ill check with the tool before soldering to the board.
As for the trimmer, Yeah I think that ones toasted ( You think that could of started this downfall ? )
I haven't desoldered and tested the trimmer off the board ( out of circuit ) but what I can tell you is that if I probe the other 3 VR Trimmers outter or outer to middle leg I get some kind of reading.
Whether its the right reading or not since its on board its still a reading. That one trimmer ( VR4 ) gives me no reading no matter what leg combo I probe.
If dead im assuming the idle current could of maxed out until smoke appeared, Actual just reading another thread here that basically says exactly what you are saying :
https://audiokarma.org/forums/index.php?threads/smoking-resistors-on-a-pioneer-sx-770.959334/ A guy @merlynski & @markthefixer stated :
"If that trimpot / variable resistor idle current circuit opens up, the output stage self destructs. It is the single most self destructive fault in a power amp."
I wonder if I should pull and test the 4 main outputs, I hope not! ( those have not been tested ).
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mikiekimi
USAF Ret 1992 - 2012...Korea/OEF/OIF
Be careful not to assume that those in-circuit VR readings are good. Just because there's something there, doesn't mean they are working per spec.
Two schools of thought - one is to get it working before you recap/replace parts that aren't bad...another is to replace while you have access to the board if you plan on recapping/refurbing later on. YMMV based on application and your intent.
Since that board is a PITA, I would replace all transistors, caps, VRs, and any damaged component. It may not be necessary to get this back up and running, but I'd approach it as preventive maintenance. I've found several caps that looked okay, only to be WAY out of spec. Since those VRs are know to cause catastrophic failures downstream WHEN they fail, why take the risk? Same with any known bad transistors.
Think of it as economy of labor. Might as well pull, test and/or replace now while the board is out. As far as the outputs go, DBT was good, by why not test just to be sure?
BUT, I admit that I have a desoldering tool that makes removing components very easy...ultimately at the end of the day it's your gear, time, and mental energy to spend how you wish
Two schools of thought - one is to get it working before you recap/replace parts that aren't bad...another is to replace while you have access to the board if you plan on recapping/refurbing later on. YMMV based on application and your intent.
Since that board is a PITA, I would replace all transistors, caps, VRs, and any damaged component. It may not be necessary to get this back up and running, but I'd approach it as preventive maintenance. I've found several caps that looked okay, only to be WAY out of spec. Since those VRs are know to cause catastrophic failures downstream WHEN they fail, why take the risk? Same with any known bad transistors.
Think of it as economy of labor. Might as well pull, test and/or replace now while the board is out. As far as the outputs go, DBT was good, by why not test just to be sure?
BUT, I admit that I have a desoldering tool that makes removing components very easy...ultimately at the end of the day it's your gear, time, and mental energy to spend how you wish
I agree 100% and will add 4 trimmers to my order, Any recommendations on ones that will fit this board? Which did you use on your rebuild?
In my case atleast as far as caps go, I want to get it working first ( Even if its outside of the unit with alligator clips ). , Im also gonna check those 4 ceramic cased resistors, the center ones have cracked outer shells and they are in close proximity to R25/R26 ( might just be cosmetic ) Once I can prove it works then I can go down the re-cap path.
I will not re-assemble until It works, My hopes are to replace the 4 VR's Any physical damaged parts I can see, as well as all transistors.
Think of it as economy of labor. Might as well pull, test and/or replace now while the board is out. As far as the outputs go, DBT was good, by why not test just to be sure?
BUT, I admit that I have a desoldering tool that makes removing components very easy...ultimately at the end of the day it's your gear, time, and mental energy to spend how you wish
Yeah I guess I really should desolder the 4 outputs and re-assemble to be safe, I only have desolder braid but at the end of the day its only a little more time and I got time. Did you re-use the mica washer and just add new thermal grease?
Also one more question ( if you dont mind ) , Did you have to test that D1 - STV3 object ( not sure if its a transistor ). In that other thread you sent me they were testing that and it required building some sort of jig/tester.
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Cool ill forget about D1 for now, Test my 4 outputs as well as the 4 ceramic resisters and read your old post.. Ill also search around on the forums and other similar receivers to see what trimmers may fit.
Appreciate all the help thus far.
100% Agree, I bought alligator clips so I can test the board like @mikiekimi did outside of the unit.. Once I get sound working perfect then ill look into a re-cap... Its definitely something I am considering just wanna fix it first.
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Jimbo40
Super Member
Just check a few of the orange caps and tantalum
You'll find some really bad ones.
I've been working on some sx1980's lately and I'm shocked how many caps are toast.
Surprised how well it played before the restoration.
But after they are fantastic.
It may not be me who gets you through the finish line, but this forum sure will.
Now I buy broken units like yours.
So,
2: sx1980 broken,
Mx1000m
3x soundcraftsmen ma5002
McIntosh ma2205
All now fully restored and in excellent condition
And on and on.
I didn't even know where the outputs were when I started.
There are some real hotshot techs in here, and they will make you think on your own, but catch you before a major fall and lots of help in-between.
It will be fun to follow your project.
Are the orange caps those little disc shaped objects? ( amateur question im sure )
Whats the tantalum? Is it the geen shaped ones ( theres one in each channel ) ?
I really appreciate your help, everyone has to start somewhere right? This place has helped me a ton! Its very enjoyable and rewarding when you take something from junk to working plus its cool to be able to buy nice gear for cheap because its broken and fix it.
Its also awesome to be able to fine tune / recap / rehab working vintage gear as well on your own.
Thats just awesome! Congrats
Ive have had convos with some really bright people on here and alot have been very helpful. I have learned that as long as you do your homework ie: use the search
function, if theres threads on the topic already then read up on it, find the schematic / service manuals, do some research and then ask your questions they are more
than willing to help. Just like you said they are here to help but show that you did your do diligence and learn from what they say.
Its been a great experience, A little forum etiquette goes a long way..
Ahh these guys ? @Jimbo40 Would these be replaced when redoing caps after the unit works, ie the resto or part of the test / repair process?
Ok cool, gonna pull and test all the main output transistors and those ceramic resisters I cant really see since they have that cermamic outer shell ).
Jimbo40
Super Member
The emitter resistors will be very difficult to test with a digital multimeter because they will be so low value, much of the results will be the test lead resistance.
Measure how many ohms the test leads are and then add the to your reading, but if the output is good the resistors are probably also.
You'll mostly be looking for them to be open.
What is the value supposed to be?
Measure how many ohms the test leads are and then add the to your reading, but if the output is good the resistors are probably also.
You'll mostly be looking for them to be open.
What is the value supposed to be?
The part is stamped ( M2 0.5ΩK / NOBLE 01 ) and the owners manual says "Wire Wound 0.5 2W" Might be simpler to just replace them.
Also pulled all 4 main output transistors and this was the results -
Output 1 - Good w/ gain of 27
Output 2 - Good w/ gain of 53
Output 3 - Good w/gain of 27
Output 4 - Short on Emitter / Collector ( see pic )
So now ill have to hunt down a replacement output transistor for this reciever, btw this was the side that had work done to it before and these were off before because they were both missing washers on the screws.
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