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SX-1010 tuner

C1 0.68/25,
C2 1.5/25 right next to it on drawing, it could have been eliminated ...
C4 10/16 connected to vr1 offset adj pot and r4 going to the base of q1
C8 330/6 FEEDBACK to Q2 base using r20,r21,r22

You will notice there is a D5 AND a D6 STV-3H diode,

The jumpers in the picture go to the metal posts (21 & 22 shoehorned in between 17 & 18) where the wires go off board to the stv-3h on the heatsink for the main output transistors. The second stv-3h is the one you saw on the driver heatsink on the board.

The pattern of the amp board on the schematic is different than what you have, extra pins for the diode among other things I have not cataloged.

edit: the 1.5uf 16v C2 is missing? it would be very close to the 0.68 cap
the 330 shows up in another picture under the driver heatsink right near the 10 and 0.68. could the 1.5 be hiding?
 
When the parts come in i will let you know before i start tearing into anything. Don't want to get ahead of you or myself.I don't have that much asprin on hand. Doesn't appear that the Amp boards will be able to fold down easily for desoldering/soldering. I suppose you have some trick for that.
 
Careful disassembly. You should see what I have to do to get at the power supply regulators on an sx-3900.....

Somebody else should have some tips on getting to (what to disassemble) the amp boards, although you may have to specifically ask the question in a new thread and wait a few days for an answer.
 
The parts arrived today. (Ups Red)I will start disassembly tomorrow being careful not to damage either of the STV-3H. (Partsstore.com TS-930s varistor the same as the STV-3h?)
Will remove old components and install new components 1 channel at a time. I will then reassemble when done.
Any measurements i need to aquire before disassembly?
Any measurements i need to get before totally reassembling?
Anything else i need to look for or do?
 
Be careful about transistor lead designations, and ANY transistor that heats up and is soldered to the pc pattern has a high probability of the solder joint failing over many years due to heating and cooling.

I usually clean those joints of old solder, bend the lead to allow more pattern contact and resolder it with fresh solder.

Watch out for foil to board seperation.

Try moving soldered component leads while looking carefully, you may find some that move showing circular "bullseye" cracks that signal intermittents. This happens when the solder is very thin.

And of course verify capacitor orientation and polarity BEFORE removing it, then verify what you found MATCHES the silkscreened information on the board.

There are several variations: (and the variations are labelled in Japanese characters)
1.66 - 1.74v
1.60 - 1.80v
1.72 - 1.80v
1.60 - 1.68v over the temperature range, so go with the 10 buck one from Pioneer.


And of course, no power until we verify the integrity of the bias circuit connections.
 
There are several variations: (and the variations are labelled in Japanese characters)
1.66 - 1.74v
1.60 - 1.80v
1.72 - 1.80v
1.60 - 1.68v over the temperature range, so go with the 10 buck one from Pioneer.

Are these the STV-3h components?
 
Maddart said:
There are several variations: (and the variations are labelled in Japanese characters)
1.66 - 1.74v
1.60 - 1.80v
1.72 - 1.80v
1.60 - 1.68v over the temperature range, so go with the 10 buck one from Pioneer.

Are these the STV-3h components?
Click to expand...

Yes, in the mostly japanese datasheet all 4 are listed as stv-3h, with additional japanese characters afterwards.... slight variations in "starting" voltage and (one)voltage range for the same temperature swing.
 
I removed the 2 2sc1451 transistors as well as the 10uf,.68uf and 330uf caps from the left channel last night. will put new components in tonight. There is no 1.5uf cap present on the pcb.

Update:
I put the left channel back together verifying polarity 5-6 times on caps and xsistors. I didn't mount the STV-3 back on the heat sink yet. Want to keep movement of this component to a minimum.
 
Last edited:
Good news/Bad news

MTF

I just completed installing and soldering the caps and transistors ZTX696B in the right channel. I believe that this channel is pin 3 on the protection ckt.
See photos, found what appears to be a blackened area.
Looking at the foil side drawing the D7=1s1885 diode.
On my boards D7=STV-3

Measurements:
STV-3
D7 right channel =0/0
D7 left channel =2.02v/1.29v

1S2471
D3 right channel =..220v/.521v
D3 left channel = .160v/.532v

Don't know where to go from here and don’t want to screw down the board or heat sink until I get clarification.
 
Opened up my 1010, and indeed, D7 and D8, which are indicated to be 1S1885 diodes are STV-3 diodes instead. If you have doubts as to the functionality of yours, remove them for out-of-circuit testing. Most meter diode tests will show a voltage drop of about 1.55V or so for an STV-3.

D7 and D8 (along with D3 and D4) form a Baker clamp. I'm not sure why Pioneer thought they needed three diode drops here (STV-3), but I'm not going to second-guess their design.

Edit: Meant to add that these are pretty reliable parts. Chances are high that some shorted transistor in the circuit is causing them to measure low when checked in-circuit.
 
Well, we have to remember that it WAS working with a bit of static originally.
The confusing part is that the work is being done on the left channel presently, while the right channel is untouched.

And I am concerned that the readings don't match.

The database schematic shows TWO stv-3h diodes per channel, which makes sense with how the circuit is set up. BUT I am looking at the foil patterns, because the pictures don't jibe with what I see, your pictures show STV-3h diodes on the OUTPUT heatsinks and stv-3h diodes on the DRIVER heatsinks, and then according to your pictures there's ANOTHER stv-3 (on the board) in the mix....


In order to get accurate readings, you may have to desolder one lead on each diode to be sure the reading is accurate.

And I AM worried about the lead orientation of the old versus the new transistors. ( I just re-checked, the 2sc1451 is ebc and the zetex is also ebc, but the foil pattern in the manual shows the foil, not the component side).

Thus EchoWar's comment about shorted transistor(s) concern me greatly.
 
Will remove the diode leads to verify measurements tomorrow morning. There are actually 2-stv-3h D5/D6 and 2 stv-3 D7/D8 diodes on each amp board.
Not sure why we should be concerned about the transistor leads, Have placed them correctly according to screen print on the pcb.
The foil pattern when printed and looked at from the backside on a light matches the screen print on the Pcb
Will have more info tomorrow.
Must be getting old, 9pm and im burnt out already

Update:
The original problem was that the protection relay kicks out. New caps and xsistors in the protection board. Pin 3 on that board was -3v:+5V
Also the tuner would intermittently cut out
 
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EchoWars said:
Opened up my 1010, and indeed, D7 and D8, which are indicated to be 1S1885 diodes are STV-3 diodes instead.
Click to expand...

OK, I get the difference, plus the foil diagran and the schematic don't match, there is no mention AT ALL of D7 either as a 1s1885 OR an stv-3 (or a stv-3h), especially connected to the collector of Q9.

What I ment was that even if the tuner cut in and out, and the amp went into and out of protection, AT TIMES there would be (decent?) sound.

This had me concerned:
Maddart said:
Measurements:
STV-3
D7 right channel =0/0
D7 left channel =2.02v/1.29v
Click to expand...

Because we haven't done ANYTHING with the right channel.
 
I think those two transistors on the amplifier board's heatsink shoud be tested.

When you did the disassembly, did you remove the output transistors from their heatsinks & sockets, or are they still mounted?

In fact, it looks more and more like testing ALL the transistors would be prudent.
 
The original STV-3H horseshoe diodes, D5 and D6, are mounted one on the driver heatsink, and one remote-mounted on the output transistor heatsink. The D7 and D8 Baker clamp diodes looked to be simple single-junction 1S1885's in the original design.

1S1885 datasheet

Mark...the 'small' schematic for the power amp does not show the D7 and D8 diodes, but the large full-unit schematic does.

If the channel with the wierd diode reading was working, chances are low of dead transistors...but it would be nice to know what a sine-wave would look like out of it.
 
EchoWars said:
The original STV-3H horseshoe diodes, D5 and D6, are mounted one on the driver heatsink, and one remote-mounted on the output transistor heatsink. The D7 and D8 Baker clamp diodes looked to be simple single-junction 1S1885's in the original design.

1S1885 datasheet

Mark...the 'small' schematic for the power amp does not show the D7 and D8 diodes, but the large full-unit schematic does.

If the channel with the wierd diode reading was working, chances are low of dead transistors...but it would be nice to know what a sine-wave would look like out of it.
Click to expand...

My adobe reader is painfully slow on some of the big schematics, so then I usually go for the small ones, thus I missed that. I hate those older service manuals done by ALMOST competent draftsmen.

I see it now, looks like when the original 1s1885's couldn't cut it, rather than adding 2 or three diodes in series (with the obligitory pc board changes), they just got stv-3's.

And one's shorted. In a spot that might not be too disasterous.

If he drops it off here, I can also put it on a Tek distortion analyzer (aa501).
 
I removed one lead on the (D7)stv-3 and the readings are:
D7=.93v immediately drops to 0v/reverse leads 0v
Tested a 1N4004 diode i have .537v/OL fluke 10 meter appears to be good
I haven't reinstalled the stv-3 lead yet.
Need to take some nail polish and apply to a slightly lifted pad/trace.(ztx696B)
The output transistors only reflowed solder joints never removed.
The unit has good sound before starting repair (thru the headphones) Just intermittant relay/tuner.
Just my .02cents but you would think with the advancements over the last 30 years that there should be a diode for this situation.
MTF-I,m just a half hour away from you(In good weather)- let me know if it would be prudent to drop this by.
Both left and right channels have new caps and ztx696B transistors.
Also no power has been applied since amp board repairs started.
 
Ok, hindsight dictates that the diode stuff is mostly chinese fire drill on my part, and further transistor testing isn't needed.

We will need to verify the continuity of the bias circuits before adding power, but that will be done after complete reassembly, including the remounting of the stv-3h on the power output transistor's heatsinks.

A thumbnail sketch of what to do (details will be furnished) is to verify the continuity of ALL solder joints, pc traces and anything else actually in the bias circuit's current "loop". If this loop opens up. it's like cutting a spring under tension in the middle, snap.....

This bias circuit's current loop results in there being positive 1.8 volts on the collector of Q4 then there is VR2 , D5 (stv-3h) and D6(stv-3h) and then resulting in negative 1.8 volts on the collector of Q5. If this circuit opens up in between the two collectors, the voltage will go towards positive and negative 50 volts (snap), turning on BOTH output transistors at the SAME TIME, allowing MASSIVE amounts of current to flow.... vaporizing things...

Normally one output transistor or the other turns on at a time. That bias circuit controls this...

That bad stv-3, it shouldn't be reconnected, we'll come up with something to substitute. Probably a string of (3?)diodes with the same voltage drop. The rub is that it's on the OTHER channel.....(right??) If it had been on the BAD channel, then we'd have something to think about...

I read 1.36 v on a stv-3h with my dmm, but they are speced for 1.6 volts at 7 milliamps of current. A 1n4004 is .510 volts on my meter so 3 of them (to be safe (1.530v instad of 1.02v)) in a string (anode-cathode connections) will substitute. Actually any power diode (1n4001 - 1n4007, radio shack has them) will do. The cathode (band) will be connected to Q9's collector.
 
The D7 and D8 diode are there to prevent the driver stage from saturating the output transistors too hard. In this case, Pioneer originally thought 1 diode drop would do it, and evidently decided later that they'd like a little more breathing room for fools who like to get a bit too frisky with the volume control.

You do not need to find more STV diodes to replace the bad ones. If this were my own receiver, I'd replace the dead diode with a good, fast (*speed is important! 1N4004 or similar is too slow!), rugged 1A diode, such as a UF4004, and call it a day. But, do replace both D7 and D8 if you do either.

If this really bothers you, make a string of two UF4004 diodes in series ('A'-frame mode), and replace the STV-3 with it. I can't think of a way to do this with three diodes that won't look like sheeite.

*1N4004 - Trr = not specified, since it is designed to deal with 60Hz
UF4004 - Trr = 50nS
 
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