SX-850 Phono stage gone bad - Looking for a nearby tech to work on it (NH)

The phono stage on my SX-850, like hundreds (?) thousands (?) of others out there, is complaining in no uncertain terms!

Troubleshooting and steps I've done:
All other component sections work fine (AM/FM, AUX, tape switches).

The problem exists whether speakers or headphones are engaged or disengaged.

Deoxit has been used (and where appropriate, Faderlube and Deoxit Gold) and there is no "switch crackle".

And I've grabbed a few pictures; the board is numbered AWF-011 B (perhaps making that a Rev. B board?)

Anyway, I read the various threads that dealt specifically with the 850 phono stage issue, and for those guys with experience, it's not a bad repair job.

Trouble is, I have no experience when it comes to transistor or capacitor replacement, nor do I even have a junk board to practice desoldering and soldering. Furthermore, even looking at a list provided by guys like MarkTheFixer or EchoWars I wouldn't be able to point at a spot on the board and say, that's one I need to change, that one too, nope not that one, etc.

I have both the owners manual and service manual, but a schematic leaves me scratching my head.

Sooooo, having said all that, is there anybody near me who can repair this or recommend someone near me to do the repair? (Believe me, I wish I could tackle this, it would be quicker and cheaper!)

Thanks,

Jeff

Top View


Left View


Right View

There a lot of very knowledgeable people on this forum. If you could supply some more detailed info as to the actual problem....

First off, what problems are you experiencing with the phono? Check the link (post #3)for this particular board on the 850 & 950, this is very easy to work on, you already have the board to where it can be worked on in your pictures. The schematic gives you the transistor substitutions you need to rebuild the phono/equalizer board. The KSA992's should be gained matched.

http://www.audiokarma.org/forums/showthread.php?t=518421

Sorry, I guess I was taking it for granted that my phono stage was bad based on what I was hearing, and then reading about the same symptoms in other posts here on AK.

Thanks for that link, tsd71! There's a lot of information that helps break down what some of this stuff means. Very helpful!

I also shot a brief video that hopefully will give some indication of what I'm hearing. The camera didn't pick all the subtle sounds, but was able to record the bigger ones! (And if you listen carefully, I believe you can hear a relay kick on (off?) near the end of the clip.

[URL=http://i195.photobucket.com/albums/z175/nitrozilla/General/BadPhonoStage_zps476720df.mp4][/URL]

You have more problems other than the equalizer board, are you getting the relay click with any other source?

tsd71 said:

You have more problems other than the equalizer board, are you getting the relay click with any other source?

Click to expand...

Nope, everything else works great, no issues.

I'm ordering replacement parts from mouser (thanks to previous posts that identify what I need!) but I've got a couple of questions.

My board has the "extra" caps on it, as you can see. (My questions are listed after the pix)



A close-up look at the caps


Can I order these as replacements?: Mouser number 647-UKZ1E101MPM

Second question: The recommended cap for C18 is backordered (17 weeks!). (That's number 647-UPW1H221MPD) Would someone be able to recommend an alternative that is in stock?

Thanks in advance for your help!

-Jeff

It always cracks me up how the magnificent people on here will NOT let someone not attempt to fix their own equipment and refuse to answer the original question
Good luck you are in good hands

looks like 2 resistors on that board are new, are they the correct value? They are robin egg blue near pins 2-3 & 5-6. Those Mouser caps should work fine in this application. For C18 order this:647-UPW1H221MPD6 there are over 2500 available.

94ZR1 said:

It always cracks me up how the magnificent people on here will NOT let someone not attempt to fix their own equipment and refuse to answer the original question
Good luck you are in good hands

Click to expand...

Lol, well, I'm sure they have their reasons. :scratch2: In all fairness, I did get a PM from someone who has done a lot of work. Unfortunately, he's about five hours away from me. Kind of him to contact me nonetheless.

As it turns out, it's also the same gentleman who has now taken the time to respond to my latest questions.

tsd71 said:

looks like 2 resistors on that board are new, are they the correct value? They are robin egg blue near pins 2-3 & 5-6. Those Mouser caps should work fine in this application. For C18 order this:647-UPW1H221MPD6 there are over 2500 available.

Click to expand...

First off, thanks for answering my questions, I really appreciate it! I will place that order today thanks to you. As to your question, I've never had work done on it, so that is kind of odd (I am the original owner). This may or may not help, but I took a shot of the bottom of the board. (The painters tape is there to hold the board vertical while I was taking the picture) Again, thanks for your help!

94ZR1 said:

It always cracks me up how the magnificent people on here will NOT let someone not attempt to fix their own equipment and refuse to answer the original question
Good luck you are in good hands

Click to expand...

We're so backlogged it ain't funny ....

And the charges from a shop that has to pay rent or a mortgage to do it, will discourage most folks.


Besides:

Believe me, I wish I could tackle this, it would be quicker and cheaper!)

Click to expand...

he asked!! :lmao:

Here is a photo of the same board, recapped on my SX-950. It's 180 degrees from yours, but I see the same light blue resistors.

I'd be happy to help, but Claremont is a bit of a hike from here! To "recap"...the brown caps are the Nichicon PW's, the two blackish caps that replace the oranges ones are KL's, and the square-ish red caps are panasonic ECQ's, they are the 1uf caps if I recall correctly. It is worth using these instead of the electrolytic caps.

For best results as mentioned by tsd71 about gain matching the transistors, a meter that reads HFE would come in handy. These are cheap transistors, you can buy a bunch and have fun measuring them until you get a pair that are a good match.

This is a great practice pcb. I suggest to get some fine solder wick, thin 60/40 glow core solder, a decent solder iron, some fine tools, wire cutters etc.
I usually use a solder sucker, more expensive tool for one pcb, but you have to be very careful not to smash the hot tip into the copper pad or it will damage it, so you have to be quick.
Solder wick puts more heat on the fragile pad.
I try to center (straighten it up) the lead in the hole, so that the solder comes out clean and the lead does not bind on the pad which can cause the pad to damage.
If you do damage a pad, scrap off the solder mask(green coating), so that you can solder to the copper trace. Bend the comp lead along this trace a short distance and solder/tack it down.

Good luck, hope it is a bad comp.

If you have trouble finding the caps you want, it's perfectly OK and often desirable performance-wise to go up a voltage range. Those polystyrene caps used for equalization rarely go bad, but they don't like heat or cleaning solvents. If you see a lot of crazing on the surface, it's no guarantee of any problem, but does tend to raise my suspicions if performance isn't up to snuff- they look good in the photos. My guess is changing the transistors and caps will fix it right up, but if not, other parts have to be investigated. That's where test equipment gives one a huge advantage.

39cross said:

For best results as mentioned by tsd71 about gain matching the transistors, a meter that reads HFE would come in handy. These are cheap transistors, you can buy a bunch and have fun measuring them until you get a pair that are a good match.

Click to expand...

Yeah, that mention caught my eye. I did a quick bit of googling to learn how to perform gain matching, and I think my DMM can read hFE. (On the rotary dial, in between the DCA and OHM section, is a selection that shows a symbol of a small arrow and the point of the arrow is intersecting with a plus sign) The manual for my DMM states:
"CHECKING DIODES
This meter is for checking standard diodes.
It is not to be used for checking
specialty diodes, such as zener diodes.
You can also check transistors and other
semiconductors for opens, shorts, and
normal operation, as well as determine
the forward voltage for diodes. (This is
handy when you need to match a diode)."

So, maybe it will work? Lastly, assuming I am able to gain match, the transistors would be matched on opposite sides of the board? In other words, match up Q1 to Q2, Q3 to Q4, and Q5 to Q6?

Thanks for the help!

-Jeff

rcs16 said:

This is a great practice pcb. I suggest to get some fine solder wick, thin 60/40 glow core solder, a decent solder iron, some fine tools, wire cutters etc.
I usually use a solder sucker, more expensive tool for one pcb, but you have to be very careful not to smash the hot tip into the copper pad or it will damage it, so you have to be quick.
Solder wick puts more heat on the fragile pad.
I try to center (straighten it up) the lead in the hole, so that the solder comes out clean and the lead does not bind on the pad which can cause the pad to damage.
If you do damage a pad, scrap off the solder mask(green coating), so that you can solder to the copper trace. Bend the comp lead along this trace a short distance and solder/tack it down.

Good luck, hope it is a bad comp.

Click to expand...

Thanks for the detailed advice, this is going to be helpful! :thmbsp:

ConradH said:

If you have trouble finding the caps you want, it's perfectly OK and often desirable performance-wise to go up a voltage range. Those polystyrene caps used for equalization rarely go bad, but they don't like heat or cleaning solvents. If you see a lot of crazing on the surface, it's no guarantee of any problem, but does tend to raise my suspicions if performance isn't up to snuff- they look good in the photos. My guess is changing the transistors and caps will fix it right up, but if not, other parts have to be investigated. That's where test equipment gives one a huge advantage.

Click to expand...

I've got my parts ordered, they should arrive this Wed. I agree with your thinking that changing out the transistors and caps should cure this. (Just a gut feeling, I have no experience in this matter)(so far!)

Check your PM, I live in Claremont and may be able to help a little. Just finished a SX-850 restoration so I am familiar with what you are dealing with.

edit2 - THAT'S what I get for posting based on prior posts WITHOUT FACT CHECKING THE PRIOR POST, and responding to the incorrect post as if it were fact!!! Grrrrr......

THERE IS NO WAY TO GAIN MATCH THE SX-850 PHONO AMP - THERE IS ONLY ONE OF THOSE TRANSISTORS PER CHANNEL, gain matching can be done on certain phono amps like the sx-1050 and sx-1250. Gain matching is more for the power amps, those in the middle of the model line, especially those that do NOT have offset adjustmens built in.


you can get great results without gain matching, they usually come pretty close when the lots are the same. It's chasing, say, an additional fraction of a percent of performance.

By your description, your meter does NOT do the Hfe/gain test, just the diode test. with an hfe test, there should be THREE connections to the meter, with 5 of the 6 possible lead arrangements incorrect - thus you NEED to identify the base, emitter and collector of the transistor, and hook it up correctly to the meter.

Like I said, gain matching is a frill, don't make it a more expensive one because you think you need to buy another piece of equipment.

edit - If you have a DMM, a 9v battery, a 100 ohm resistor and a 1 meg resistor you can MAKE a device to gain match transistors.

Mark, you know way more than I do but aren't Q1 & Q2 (KSA992)gain matched on this board? I thought all transistors with the orange dot were supposed to be gain matched. Or did I misunderstand a previous post in another thread?