Help with my SX-3900

[gagecalman]

Good morning Mark. I replaced all of the components but still have the same problem. No relay activation. I removed wire to pin 8 and I have 30 volts on the wire. Any suggestions. Thanks

 

[markthefixer]

Good morning Mark. I replaced all of the components but still have the same problem. No relay activation. I removed wire to pin 8 and I have 30 volts on the wire. Any suggestions. Thanks

Did you test ALL of the resistors for proper values, anything less than 20k is vulnerable to burn out.

And were you sure about your transistor lead arrangements?

Also check the voltages at the amplifier outputs again. They should be in the millivolts range, it is entirely possible that this is a new set of symptoms due to the boards being removed and worked on.

How did you do (remove?) it? I expected to discuss the replacement process in more depth before you dove in.

 

[gagecalman]

Good morning Mark. I tested all the relays and all were fine. R199 is a 15k that read about 10k but its duplicate R191 also read the same. I have someone I work with that repairs and calibrates electronic test equipment. He said when they are in a circuit sometimes you would have to remove 1 lead to check. We did not. The transistor are all in fine. Flats are opposite of original. Output before relay with no imput is 11mv on 1 side and 20 on the other. We unwraped the wires on the 8 pins and removed the connections on the bottom of the board. Then we carefully slid it out of the top. I had my coworker replace the components. Sorry I did not wait. I was wondering why removing Q139 lets the relay activate? Thanks for all of your help!

 

[gagecalman]

Good morning Mark. I did not hear back from you. Is there anything else I can do with this? Thanks. Jim

 

[markthefixer]

Do you have the old Q139? what were the markings on it?

Just to clarify, it was working until the pop and smell, then it wasn't working anymore and nobody else has done anything to it?

At Q139, I need emitter base and collector voltage readings.

Then take off the pin 8 wire, retake the readings on Q139 and also measure the voltage of the disconnected wire hanging in midair.

Q139's function is to discharge C140 immediately after power off, before ANY other voltages decay and cause weird things to happen, thus disconnecting the speakers from the weirdness of an amp in the throes of power down.

The pin 8 voltage is supposed to have very little storage capacity or current drive and disappear fast when not refreshed by line power. Q139's normal state is not conducting.

An answer to your post will take a while, as i have to get readings from a similar working circuit in operation.

 

[gagecalman]

Good morning Mark. I don't remember the markings on Q139. I have some of the ones I pulled and one is marked A1100 02 F or R. I smelled something and it didn't work after that. I replaced the bulbs 18 months ago myself and no one else has worked on it. I took the readings but now I am not getting the correct voltage on pin 1&5. Pin 1 is -4.3 and 5 is +2.7. I also don't hear the first relay that comes on within a few seconds. That all worked when I tested it after replacing the components the other day. This seems to be a brand new problem. Here are the voltages (mv) on Q139 emitter, base, and collector. 8 , 0 , 570. With the wire off pin 8 550 ,0 ,150 and 32 volts on wire. Thanks for your help

 

[markthefixer]

Good morning Mark. I don't remember the markings on Q139. I have some of the ones I pulled and one is marked A1100 02 F or R. I smelled something and it didn't work after that. I replaced the bulbs 18 months ago myself and no one else has worked on it. I took the readings but now I am not getting the correct voltage on pin 1&5. Pin 1 is -4.3 and 5 is +2.7. I also don't hear the first relay that comes on within a few seconds. That all worked when I tested it after replacing the components the other day. This seems to be a brand new problem. Here are the voltages (mv) on Q139 emitter, base, and collector. 8 , 0 , 570. With the wire off pin 8 550 ,0 ,150 and 32 volts on wire. Thanks for your help

No NEW smoke, right?????

1. You should have ALL of the old parts that this "tech" replaced.
2. There was NO checking done of the parts numbers that were removed (you or him) as to what they were WHEN they were removed. I guess I should have EXPLICITLY said that. Even when first pulling Q139, the most key element to identifying the difference...

The sx-3900 manual lists the transistors in the protection circuit as ALL 2sc2575. The inclusion of an a1100 means that you have the later variant of the protection circuit, like what is found in the sx-d7000. Pioneer is ENTIRELY derelict in this matter, they have TWO different pc board patterns for the awm-097 board, as well as the new circuit grafted onto OLD boards... This change in the protection circuit involves both the amplifier board AND the power supply board.

The first letter of a transistor tells it's polarity, a & b are pnp and c&d are npn. Polarity is the MOST important characteristic of a transistor.

Did you get more than three of these:
D129 & D130 & D132 1s2471 small signal diodes 75v .2a
512-1N4454 $0.03 ea
as we need to replace D134

and we need a different transistor: (until now the pnp / npn stuff was self-explanatory)
Q139 2sa1100 PNP to-92 BCE 50v 0.2a 0.3w 90-500hfe 200mhz
512-KSA1013YBU PNP to-92 ecb 160v 1a .9w 50mhz 160-320hfe $0.18

And I am HOPING that the power supply readings are the result of a bad meter ground or some other artifact.

 

[gagecalman]

Hi Mark. I do have a diode for D134. I will have to order a transistor for Q139. Before I placed the order I checked the voltages again on 1 & 5 and they are less than 5 volts. Using the same ground I checked pin 8 and it is 30 volts. I removed wires on 1,5,& 8 and checked again with the same results. The first relay is not activating either. I looked for loose wires or joints but still no luck. I did not know if I need to address this new problem before ordering parts? Thanks

 

[markthefixer]

We have a bit of troubleshooting ahead, with the +/- 54v gone the flouroscan displays have shut down, but you didn't mention that. The speaker lights should be working and the illumination lamps should be working. Also not mentioned.

BUT the function lamps (am/fm/aux/phono1/ phono2) run off the +12.8v. One or more may be burned out, but phono2 and am may be your best bets for functional lamps. Do ANY light when selected?

The +54v supply's D6 14v zener diode reference voltage controls everything, and it is shared by, and it can be affected by, the +12v regulator >>> generating a chicken/egg quandary.

The -54v supply depends upon the +54v being present to mirror the voltage.

The +5.5v supply depends upon the +12.8v supply being present.

Getting +2.7v out of the +54 regulator is consistent with a shorted D6 zener diode, or a shorted C16 in the 12.8v supply, which parallels the diode.

Unless it is a temporary fault, caused by some piece of junk bouncing around inside, we are at a point where someone familiar with working on a 3900 is required. Getting at the power supply regulator board makes getting at the amplifier board look like child's play. It is shoehorned in behind the front panel on the left side.

The faceplate comes off, then the entire front of the chassis has to be removed. And that involves the display board which is hard mounted to the front of the chassis AND the rest of the chassis. Multiple wires including grounds have to be opened up, and hardware hidden on boards (with grounding purposes no less) must be correctly removed... etc...

It ends up looking like an autopsy, things all over the place...

Then the whole thing has to be insulated and TURNED ON!!! Then start troubleshooting. When the parts to be replaced are identified, further contortions are necessary to actually replace the parts.

All this involves a moderate amount of risk of inducing further damage.

It is about the least favorite thing I do. I'm not saying no, just trying to convey the situation. I WISH that power supply had behaved itself.:sigh:

So see if there is junk bouncing around behind the power supply board.....

 

[gagecalman]

Good morning Mark. You were right about the flouroscan display and the function lights. None are working at this time. Speaker and illumination lamps are working. I still don't understand what happened. The power supply was working when I first powered it up after replacing the components because I know the flouroscan display was on. I looked but couldn't find anything that looks like it should be a problem(Junk). I realy wanted to fix this being I bought it new but it sounds like it is becoming cost prohibitive. I guess I should start looking for a replacement? Thanks Jim

 

[markthefixer]

We have a bit of troubleshooting ahead, with the +/- 54v gone the flouroscan displays have shut down, but you didn't mention that. The speaker lights should be working and the illumination lamps should be working. Also not mentioned.

BUT the function lamps (am/fm/aux/phono1/ phono2) run off the +12.8v. One or more may be burned out, but phono2 and am may be your best bets for functional lamps. Do ANY light when selected?

<snip>

Good morning Mark. You were right about the flouroscan display and the function lights. None are working at this time. Speaker and illumination lamps are working. <snip> I realy wanted to fix this being I bought it new but it sounds like it is becoming cost prohibitive. I guess I should start looking for a replacement? Thanks Jim

Do any of the function lamps light?