Pioneer SC-1227 A/V Receiver issue ... need some help ...

[Journey11]

Hi All,
Been a while ...
I've been working on a Pioneer SC-1227 A/V Receiver with the initial problem being, the sound started to intermittently drop out for a short time then come back. When I tested it for several hrs it seemed fine then boop ... sound cuts out for a short time then comes back and is good for a while then goes again. The owner also said a few times it made a loud pop noise in the speakers followed by a very loud screeching sound. After this occurred a couple times he disconned it as he was afraid for his nice speakers ... good move. And I believe this started after the intermittent sound issue started. First step for me was to look at the diag mode to see what faults if any were recorded.
There were 3 O/L occurances and I think 1 over temp. I did a hard factory reset and ran it again but intermittent sound issue persisted ... curious I was never able to get it to pop and scream. Possibly because I couldn't turn it up very loud maybe ? I live and work in my condo, can't make a lot of noise.
So my first inclination was to replace ALL the Mosfets on the amp ... now here's where it gets weird ... $50 later ...
After doing this now the unit will not stay powered up ... starts up ... stays one for about 3 secs then protection shuts it down. I took it all apart again and kicking my self for not going diag mode to get errors again ... DOH! I checked and rechecked for mistakes or problems with the new FETS and found nothing.
I'm willing to bet that the O/L protection is kicking in again ... only thing is when it was working but had the sound cutting in and out the 3 O/L trips never shut the unit off ... wth?
I've been scouring the net looking for explanations of what failure or error conditions typically trip the O/L protection circuit and found very little helpful info.
Anyone here familiar with O/L causes ?
Can anyone hazard a guess as to why a set of new FETS would cause the unit to fail even worse by not staying on ?
The O/L circuit in the service manual looks pretty simple but I can't really figure it out.
One thing I did not due because 1) I was lazy and 2) The DC detect had zero counts was to actually check the PS voltages around the unit. This design made it difficult to do so ... so maybe hence my hesitation to measure PS voltages but I can probably safely assume PS voltages are good since no DC detect errors were recorded.
Also I can assume the PS was all good since it ran before I changed the FETS.
All the PS filter caps look good ... no signs of leaking or swelling but that's no gaurantee ... it is a pretty old unit but worth fixing.
Another idea I had was that one of the FET driver chips may be malfunctioning ? Could that cause O/L condition ? As far as I can tell the O/L condition is caused by a voltage (high) on the speaker outputs ? But with these class D amps that may not be the case ... the Utube vid I saw on protection was for a Yammy that was not class D as far as I could tell and it had 4 redundant backups for voltage detection on the speaks OP.
My next step is to reassemble and see if I can get into the Diag mode and see whats going on now.
But any ideas out there will be welcome ...

Journey
PS>>> Here's a section of the schematic where OL circuit is located and a pic of the amp brd.

 

[Martaine2005]

IMHO, the power supply voltages should have been checked first.
Perhaps you should put the old mosfets back and partially assemble to get those measurements.
Did you use the correct mosfets and put the pairs in correctly?
Do you have an ESR meter?

Martin

 

[Journey11]

IMHO, the power supply voltages should have been checked first.
Perhaps you should put the old mosfets back and partially assemble to get those measurements.
Did you use the correct mosfets and put the pairs in correctly?
Do you have an ESR meter?

Martin

Hi Martin,
Thanks for responding.
You are correct ... I should have. So far in my experience working on AV recvrs, if there are no DC detect errors then the PS is good to go. And as I mentioned above, the thing was running fine aside from intermittent audio drop out. But wasn't able to confirm the loud pop and scream issue. As far as the mosfets go ... I did use the correct replacements and triple checked the them for alignment and correct orientation.
I have been thinking of putting the old ones back but gonna be a royal pain. And the reassembly and disassembly process is also a royal pain ... this recvr isn't built like most ... it's really messed up. The amp brd is completely buried under multiple layers of brds after assembly.
I'd like to get some input if possible from someone here familiar with OL protection causes before I do that.

There was something that happened after I put the new fets in and reassembled to power up ... it wouldn't power up at all, period. Then I did go around looking for that problem measuring voltages and it basically was the mains were not switching on. It ended up being I had to push a combination of power button and another to clear something/reset something ? After that it powered up but would shut down within about 3 secs.
I'm going to reassemble and try and get some error codes ... let ya know what I find.

 

[Journey11]

Hello again Martin,
Well I reassembled and wasn't able to get it into Service Mode ... it shuts down to fast to get the thing setup to enter Service mode.
BUT what I was able to find or see was a blinking iPod/iPhone/iPad LED that according to the service manual says it's having an OL condition or Over Current ... same thing.
The other OL fault cause listed was something called Zobel resistance but that only apparently pertains to sustained high output at higher frequencies so I don't think it's that one.
So my suspicion was correct ... that it was probably tripping OL protection.
So back to the drawing brd ... sigh ...

OH yeah you asked if I had an ESR meter ... yes I do ... what should I be checking with that other than capacitors ?

 

[Martaine2005]

If you are correct about "over current", that suggests a short somewhere. But I would expect the main fuse to blow under a short condition.
Out of curiosity, did you check the new mosfets before installing them? There are many fakes around.
I would be inclined to replace the original ones and see if the original fault returns before continuing.
You might end up down the rabbit hole.

You should check the caps for ESR as a matter of course while the unit is apart.

Martin

 

[WHONOES]

Have you checked for a large d.c.offset at the output. A lot of amps have a circuit to check for this and will shut down after a few seconds if there is one. Anything more than 100mV or so will constitute an offset error.
If you are going to check for this make sure that the volume control is turned down to zero.

 

[Journey11]

If you are correct about "over current", that suggests a short somewhere. But I would expect the main fuse to blow under a short condition.
Out of curiosity, did you check the new mosfets before installing them? There are many fakes around.
I would be inclined to replace the original ones and see if the original fault returns before continuing.
You might end up down the rabbit hole.

You should check the caps for ESR as a matter of course while the unit is apart.

Martin

Hi Martin,
Thanks again for your input.

YA so my understanding of OL condition is usually a short but none can be found.
No I didn't check the FETs ... I almost always by from Digikey, trusted big US supplier and these came from there.
Never had any fake issues from there but always a 1st time or more likely one of them was faulty right out of pkg.
Seen that before. I have gone through them with a meter while still in circuit and nothing seems out of place but best if out of circuit 4 sure.
So yep looking like I'll have to put the old ones back and see where it goes from there.
As far as the ESR for caps ... there's a lot of them any suggestions which ones to start with ? After I check the two big ones one the
high voltage rails. And to refresh my memory on doing ESR ... they gave to be out of circuit right ?

 

[Journey11]

Have you checked for a large d.c.offset at the output. A lot of amps have a circuit to check for this and will shut down after a few seconds if there is one. Anything more than 100mV or so will constitute an offset error.
If you are going to check for this make sure that the volume control is turned down to zero.

HI again,
Nice to here from you again.
Yes, you are correct ... in that instance the service mode would have shown DC detect errors and there were none before the FET replacement. However, something happened when I 1st powered up after reassembly. The units mains relay clicked on and then nothing. There after it was totally dead no click from the mains relay so I went searching. Ended up find in the diagnostic section of the manual that if a DC error is detected at power up it will shut down and stay locked out. The recovery for this is to activate the DC detect Cancel operation. One of the leds on the front panel (MCACC) was blinking and one fault indicated by this is DC error.
So it's possible something is amiss with the new FETs and is causing a DC error ... Unfortunately now, the unit won't stay on long enough for me to set into service mode to check for DC detect error ... and in order to get there the volume has to be at 00. I tried to turn it down in the short time it is on but can't get it down so I'm kinda screwed here.
As per Martin's suggestion ... I'll have to put the old FETs back and see what happens.
In the diagnostic section about that DC error ... It says it looks for DC at SP output after LPF, if it is above + or - 7v then it shuts down and only way to start again is to Cancel DC detect lock out.
So if say one of those new FETs was faulty would that could that cause an offset problem ?

On a side note ... this unit has no markings to indicate Part refs ie.R4222 Q1002... and a lot of the schematic ref's don't give a value ... terrible SM ! Oh and no pcb layout diagrams to indicate locations.

 

[Martaine2005]

Given that we don't know the cause or even if it's one channel causing the problem, it's a process of elimination.
You can sometimes check caps in circuit but it's best to check out of circuit. I use my solder vacuum pump and clean one leg which takes it out of circuit. Much quicker than removing them. The whole process shouldn't take more than 10 minutes for about 20 capacitors.

Martin

 

[Martaine2005]

Just to add to my previous post:
As you seem to have a different problem upon reassembly, have you checked for cracked/dry solder joints?.
Very common problem that causes all sorts of issues. The fact that you moved something may have connected or disconnected that particular connection.
It would be worth a thorough inspection with a magnifier.

Martin

 

[WHONOES]

Being a Class D amp. the output Mosfets should be identical. Can you see if either of the Mosfet gates are switching?

 

[Journey11]

HI Guys,
I'll reply here to all the new postings ...
With respect to Martin's posts ... one of the first things I look for are burnt components and or broken/cold solder joints.
In many cases, this is where I will end up finding an issue(s). I worked in a manufacturing factory for 6 years and did a LOT of inspection of solder jobs so I have a keen eye for poor reflow jobs. This unit looks like a very well done reflow process and have scoured it intensively under magnifier and haven't found anything ... yet, I'm always looking as the work progresses.
Since the error codes focus on the output amp, I'm heavily leaning in that direction. I did take a good look at the many interconnect jumper brds ( of which there are lots) for broken joints.
There are 6 jumper cable in all to the amp ... 5 are all power and one is a ribbon for signal. The input sigs all come through another jumper brd. ( IR interface, the vertical brd at the back )
As far as your ESR checking method goes ... that may work for some instances but I have found many times that the leads are just thick enough to make clearing the hole impossible, especially if they used hi temp solder, man that stuff can be a bea-ach.

In response to Whonoes ... Unfortunately, in order to get the whole thing working ... it ALL has to be assembled due to all the error checking and on top of that, the amp assy is enclosed in a box and buried under all the rest of the layered pcb's. They all sit layered on top of the amp closure.
I had an idea tho but it's a major pain. I could solder wire leads to each gate and run them out the back of the enclosure. And that means 2 wires for each amp ... seven of them !
I'm thinking maybe just do wire leads on the outputs and scope for the expected waveform there ? ( as shown in the SM ) and as I mentioned earlier, I can't measure for DC offset since I am unable to get the volume down to 0. I can however scope the DCERR signal to see if it's going low ... in fact I am going to solder wire leads to all the ERR lines to see just which one(s) are tripping. Luckily all those lines are accessible in between the front panel and the main brain brd.

Anyway, me being me, when I encounter this sort of problem child ... the War is on and I hate losing and I NEVER quit !
Which brings me to a totally different note to mention ... Remember that Yamaha Stagepas 600 that I posted and you two replied on ? It's still blowing output transistors (3rd set so far). Still cannot find any faults causing this seriously weird situation. I have walked away from it for a long time now but I have 2 more sets of trannys ... hence my little motto from above ...
the War is on and I hate losing and I NEVER quit !

 

[WHONOES]

Do you have a complete schematic without anything over the top of it.

 

[Journey11]

Yes I do ... I did not edit any posted partial schematics ... I just tried to post an update and lost it all.
The file is too large ... here's a link ....
https://elektrotanya.com/pioneer_sc...-1222-k_rrv4324_av_receiver.pdf/download.html

 

[Journey11]

Here I go again ...
I did some work to measure voltages and ERR sigs ....
All voltages on the POS side are a little over the rated ... the NEG supplies are a few volts shy of rated ... but not out of spec for voltage regs.
Chassis gnd to power ground shows +1.25 vdc which is weird.
I soldered extender wires from the ERR lines outside the box ... and surprise ... they were all normal and all went low after shut down.
uSecs or mSecs of timing involved and cannot be detected with DMM. So the ERR lines aren't any help at this point.
However the NEG voltage lines are low and there is some anomalous 1.25 vdc on the power gnd to chassis gnd.
Even tho I couldn't get the volume down to zero ... I checked FL+ to FL gnd for DC offset and zip ...not even a mV.
B+ and B- are bang on +63.5 and -63.5 ... however At con CN4002 -B+15v measures -48.4v pin1 and pin2 at same con is -63.4 which probably should be zero ... both to chassis gnd.
Per the schematic pdf ...page refs ...
pg 140 to start 2 page of ERR sigs and start of amp schemes
pg 46 for more diags
pg 38 for ERR code descriptions
Pg 141 for power to the amp

My brain hurts !

 

[Journey11]

HI,
Quick update ... The 2 pin PS B+15 and B- checked out ok when GND ref was B- ... so overall the voltages are good save for
the odd 1.25v floating on power gnd and the uneven balance between the pos rails and neg rails for 12 and 8v supplies.
And only one I haven't checked yet is the +/- 5v on the amp brd ... forgot to run a couple wires for those.

 

[Journey11]

Hi,
Another update ...
Some new findings ... a blinking iPod LED also can indicate a fan failure. The fan works when connected to 12vdc BUT the lock detect signal from the fan seems to be wonky. When fan runs ... lock detect from the fan is pretty much zero vdc with ref to Fan- ... put a drag on the fan or stop it dead and one would expect that to go high ... it doesn't do crap ... stays at zero.
Also had a look at the old FET's ... many display heating distress as there is discoloration in the casing metal ... green to brown and even a bit of carbon brown/black (on the underside). Seven out of the 14 show a low to medium resistance between Gate to Source ... not good ... 250 ohms low to up to 2 or 3K. This might explain the loud pop and screeching of the speakers when/if they broke down ... also intermittent sound drop out as well. A good FET shows infinite ohms between gate and source. Gate to source should show infinite correct ?
The other thing was this ... after power up the fan would NOT start up ... measured for volts and NADA.
I was able to get the thing to stay on trying to get into SMode and got the volume down to --- or zero (only on zone 2 mind you) but still couldn't disable zones to off and still cannot get into SMode yet. When I 1st tried to get into service mode was a real bitch and can't quite remember how I got around that issue. Instructs say set volume to zero and Multizone to off ... then hit power button and mutlizone button at same time for 5 secs ... no go on that action.
My guess is that the fan should at least kick on at low speed on initial power up BEFORE the speaker relays kick on but this is not the case. The flashing iPod LED is one indicator that the fan is failing but should also display fan err on front display which doesn't happen ... maybe just isn't staying on long enough to do this.
As mentioned earlier ... the 4 ERR sigs are high until the unit shuts down ... not much help there with those. If any one of them goes low from 5vdc to zero the unit shuts off. They all go low and unit shuts down. I have a 4 chan scope but unfortunatley
.only have 3 probes. Would like to scope and see if one of them goes low before the others.
I'm starting to look in the direction of a fan signal failure since the fan is not kicking at start up and the FET's showing heat distress on their undersides ... never noticed this until i started testing them. Odd thing is these DirectFet units don't test like a normal FET ... can't turn them on with multimeter ... possibly cuz gate voltage is 20vdc and meter can't charge em up enough to turn em on ?
Tried a slightly discharged 9v bat and it wouldn't do it either. Gonna have to bread brd a test circuit to do this me tinks.
As far as putting old FET's back ... I don't think that's a good idea since I found 7 of 14 to have a low to medium resistance across gate and source ... just not right ...
On another note ... lots of trannys in the fan circuit are internally compensated and cannot be tested in circuit ...any one of them could be toasted but I'm thinking something is wrong with lock detect on the fan as it reads zero no matter the fan is doing.

Awaiting some input ....

Journey

 

[pedroafonso]

i got almost same problem but mine is SC-82 with dc err on out put. Chassis gnd to output shoe 1.9 volts. i dont know if that is ok. i think the dc err detect when voltage is more than 7 volts dc on output.
If i disconnect that two wire plug you said is 15 volts supply CN4002 i have no more errors and the unit fire up no problem. i got the same measurements as you on that +15 volts supply to the amp board. i cant find yet the problem on mine.
when my radio is working i can see the fan on all the time. i think your fan circuit is the problem, detect the fan is not spinning!!
I think we can help each other here, this radios almost identical.
i can see on the xdcerr line goes from 4.5 v to 0 then the radio shut off.
you can check what error lines goes low. on the right side of the radio there is this vertical board where you can measure those lines

 

[Journey11]

Hi Pedro,
Thanks for your input ... I did measure all of the err signal lines and if I remember right I didn't see any red flags.
I will try disconnecting the 15 volt supply line and see if that does anything. It's just so odd that after replacing all the FETs that it would start misbehaving and the fan is not starting up either. If I remember right as well, there was no voltage or signal for the fan speed ctrl.

 

[pedroafonso]

Hi Journey
Disconnect the cn4002 Wich is the 15+ line that feed the drivers IC thought a 12 volts low noise regulators. If I disconnect that cable then my radio works!
I will attach a picture to show you where to get the error signals. Mine shows 4.5 volts in all of those five pins but the one for IR always shows 0 volts. On the pin for xdcerr when I connect the 15+ line shows 4.5 volts for like two seconds then got to 0 and radio shot down.