Sansui G-9000DB protection issue!

Depends which 4 of 8 and which 2 of 4 - could be too much voltage being applied, from a blown regulator, and no longer regulating. :scratch2:

470µF, 35V - replaced with 560µf, 50V - not a problem, (except why?) providing you did each channel the same.
 
470µF, 35V - replaced with 560µf, 50V - not a problem, (except why?) providing you did each channel the same.

Yes, I did both. Here is a pic of the board (F-2796) ,The 2 bulging caps are circled. I'll order some more caps as the original value ,let's see if that is going to help fix the problem.

IMG_5948.jpg
[/URL][/IMG]
 
It is possible the silk screen on the board is wrong. Measure the voltage on the + side and - side of each cap. Make sure the polarity of the cap matches the voltage and the voltage does not exceed the rating of the cap. Then put your meter on AC Volts and measure the voltage across the cap. It better be 0V. If not, you have a blown rectifier putting AC across the cap.
 
It is possible the silk screen on the board is wrong. Measure the voltage on the + side and - side of each cap. Make sure the polarity of the cap matches the voltage and the voltage does not exceed the rating of the cap. Then put your meter on AC Volts and measure the voltage across the cap. It better be 0V. If not, you have a blown rectifier putting AC across the cap.

Warren! Sorry for a stupid question, Do I need to do this with everything plugged in and the receiver turned on or I just need to remove the cap?

Here is a picture of the board before I recapped them, I think I did exactly as the stock one. I'm also looking at the schematic of the board but I can't identify which is the rectifier?

IMG_5298s.jpg
[/URL][/IMG]
 
I'd pull the board out and leave it till I measured the output of the +/-33V regulator. The input to the pass transistors is over +/-70V, so the potential there is certainly enough voltage to cook a 50V cap.
 
G9000_33V_Regulator_zpsafmw8dgj.jpg~original


Here's the regulator for the +/-33V. It is fed from the F-2807 vertically installed board on the topside, through four discrete diodes (bridge) and one 1000µf 80V cap for each 72V rail. So the chances of ripple being the failure mechanism is pretty remote.

The negative regulator is tracked from the positive regulator, so if the positive reg is bOrked, the negative isn't going to be good either.

Note that the schematic doesn't show the VR03 voltage adjust pot, which is a simple series adjust potentiometer in series with the R13 resistor. I'd not be trusting the scat numbers for the feedback resistor values, instead, rely on the values of the installed components if replacement is needed.

The circled D03 and D04 diodes need to be replaced with a series'd pair of 1N4148's. And if the output voltage was high enough to swat those 50V caps on the phono board, I'd expect the poor little 220µf 35V caps at the output of this board to be in dire need of attention as well.

This +/-33V is used ALL OVER the preamp section, so if it was blazing out-of-control, I'd be looking at replacing a bunch of caps all over the preamp and fearing lots of blowback from damaged semiconductors.
 
Thanks for the info,Glenn. I did replace the D03 and D04 last year with 1n4148 in series. And I just pulled the R13 and it checked out ok but not the same value with the schematic, the schematic says 8.2k but the actual resistor is (blue,violet,red and gold)=6.7k ohms and the reading is 6.74 k ohms.

Here is some pictures of the power supply and protector board.

D03 and D04 are circled
IMG_5949.jpg
[/URL][/IMG]

Caps are looking ok!

IMG_5950.jpg
[/URL][/IMG]

IMG_5951.jpg
[/URL][/IMG]
 
Sure. But that won't fix your problem. We really need to know what the DC output of this regulator is.
 
Glenn! Here are the reading. Hopefully I did it the right way. Black lead to chassis .

IMG_5954.jpg
[/URL][/IMG]

IMG_5955.jpg
[/URL][/IMG]

Point 37 is reading +5.34v instead of -33.5

IMG_5958.jpg
[/URL][/IMG]

point 39 is reading +64.9v instead of +33.6.

IMG_5959.jpg
[/URL][/IMG]

Definitely something is wrong here.
 
Well, now you know why you're killing the negative rail caps.

I'd do a full swap of every semiconductor on that +/-33V regulator, and a careful test of the associated resistors. And the caps at the output of that reg need to be removed and thrown away.

The preamp boards all have input filtering caps on them as well, and these need to be swapped out.
 
Well, now you know why you're killing the negative rail caps.

I'd do a full swap of every semiconductor on that +/-33V regulator, and a careful test of the associated resistors. And the caps at the output of that reg need to be removed and thrown away.

The preamp boards all have input filtering caps on them as well, and these need to be swapped out.

Thanks Glenn! the caps @ the output that you are talking about. are the C12,C13,C14,and C15? Do I have to replace the ceramic disk ones too or just electrolytic ones only? and all the transistors in the pix that you posted? I appreciated your help. I'll report back when I replace them.
 
The ceramics (C14 & C15) are probably rated for at least 100V, and are non-polar, so I'd doubt if there was a problem with them.

Note that all the preamp boards have some sort of local filter where the +/-33V comes into the board. I'd make the assumption that these parts are no longer viable.

As far as a fix, yes, I'd clean house and change out every semiconductor in that 33V regulator. Your 1N4148's are likely OK, but give 'em a diode test and confirm that they are installed properly.
 
Last edited:
The ceramics (C14 & C15) are probably rated for at least 100V, and are non-polar, so I'd doubt if there was a problem with them.

Note that all the preamp boards have some sort of local filter where the +/-33V comes into the board. I'd make the assumption that these parts are no longer viable.

As far as a fix, yes, I'd clean house and change out every semiconductor in that 33V regulator. Your 1N4148's are likely OK, but give 'em a diode test and confirm that they are installed properly.

Glenn, I have some questions, I want to order the ceramic disk ones just in case, but mouser doesn't have the 0.047uf 100v in ceramic but they have plenty of multilayer ceramic. Is it ok to use them MLCC?

Is it best to replace the A850/C1735 pair with KSA1013/KSC2383 or A992/C1845 ? I have plenty of the A992/C1845 but not the A1013/C2383.

Thanks again!
 
The type of ceramic cap is not terribly important, but there's a Kemet ceramic that looks to be pretty small and rated for 500V: #80-C322C473KCR.

As far as the replacement semi's:

TR01 -> KSA1013YBU or KSA992
TR02 -> KSC2383YTA or KSC1845
TR03, TR07 -> KSC945CYTA (center-collector, hence the 'C' suffix)
TR04, TR08 -> KSA733CYTA (ditto)
TR05 -> MJE15032G
TR06 -> MJE15033G
ZD01 -> 1N5234B (#512-1N5234BTR)

I'm also concerned about your values for R05 and R06. From your pics, they look like 100 ohms...is that right? Scat calls for 330 ohm at R05 and 270 ohm at R06, but IIRC it seems that both resistors were 330 ohm 3W. Bottom line is that with a 70+V input voltage and 33V output, we need to drop some of that before it hits the pass transistor to help keep it from burning up. 100 ohms, if that's what is in there, is way too small.
 
The type of ceramic cap is not terribly important, but there's a Kemet ceramic that looks to be pretty small and rated for 500V: #80-C322C473KCR.

As far as the replacement semi's:

TR01 -> KSA1013YBU or KSA992
TR02 -> KSC2383YTA or KSC1845
TR03, TR07 -> KSC945CYTA (center-collector, hence the 'C' suffix)
TR04, TR08 -> KSA733CYTA (ditto)
TR05 -> MJE15032G
TR06 -> MJE15033G
ZD01 -> 1N5234B (#512-1N5234BTR)

I'm also concerned about your values for R05 and R06. From your pics, they look like 100 ohms...is that right? Scat calls for 330 ohm at R05 and 270 ohm at R06, but IIRC it seems that both resistors were 330 ohm 3W. Bottom line is that with a 70+V input voltage and 33V output, we need to drop some of that before it hits the pass transistor to help keep it from burning up. 100 ohms, if that's what is in there, is way too small.

Glenn,Thank you very much. The R05 and R06 are 270 ohm 3w as the original. Here is the picture of the original.

IMG_5251s.jpg
[/URL][/IMG]

I think I see some G-9000 have 270 ohm on one side and 330 ohm on the other side and I also see some with 270 ohm on both side. Here are the ones that I found at Scott Thompson's photo album. His G-9000DB and his G-901DB are the same as mine.

2012-10-20001026.jpg
[/URL][/IMG]

and his G-901DB.

2012-06-15001021.jpg
[/URL][/IMG]
 
Last edited:
They probably could stand to be larger...as long as you had a good 10~12V differential from collector to emitter on the pass transistors, things would be fine. But to get the right value might require some experimentation. For now, as long as you know that those resistors are 270 ohm, focus on getting the regulator working correctly. If you want to tweak it later you'd want to measure the voltage drop across those resistors and calculate the current. This would allow you to perhaps come up with a value that takes a bit of strain off of the pass transistors.
 
Hi Glenn! After replacing many parts today, The voltage reading is better but still not at the schematic values. at D03 is 72.5v and D04 is -72.7v and point 37 is -32.42v and point 39 is 32.02v. I haven't changed the R05 or R06. Should I replace the 270 ohms 3w with 330 ohms 3w? Thanks.
 
Back
Top Bottom