9090DB, Went from Playing Normally to Quiet

[BearsFan]

Hi Guys,
I am posting based on my 9090DB dying yesterday afternoon. My tried and true workhorse is ill!

I was playing it for about an hour and had it turned up but not cranked (85db level on my sound meter). All's well and the sound suddenly cut out. I went to check and could hear a faint distorted sound from the right channel only.

• The Protection Light is green
• The quiet “tinny sound’ comes from the right channel only, the left side is dead.
• I tried in stereo and mono, left channel is always dead.
• Same results regardless of the dolby switch position
• Speakers are connected to channel B (A,B,C)
• The unit has been in operation for the past month with no symptoms other than a known tuner power supply issue.
• There was no smoke show or burning smell, just went from playing to quiet. I had it turned up but no louder than 90db on my sound meter, it wasn’t “cranked”.

If this is a run of the mill Sansui receiver issue already addressed, can someone steer me to that thread? I've looked around and didn't see this specific problem, although with the many years of postings, it might be in here somewhere. Thanks to all for any assistance you may be able to lend.

 

[Skywatcher]

Hi Guys,
I am posting based on my 9090DB dying yesterday afternoon. My tried and true workhorse is ill!

I was playing it for about an hour and had it turned up but not cranked (85db level on my sound meter). All's well and the sound suddenly cut out. I went to check and could hear a faint distorted sound from the right channel only.

• The Protection Light is green
• The quiet “tinny sound’ comes from the right channel only, the left side is dead.
• I tried in stereo and mono, left channel is always dead.
• Same results regardless of the dolby switch position
• Speakers are connected to channel B (A,B,C)
• The unit has been in operation for the past month with no symptoms other than a known tuner power supply issue.
• There was no smoke show or burning smell, just went from playing to quiet. I had it turned up but no louder than 90db on my sound meter, it wasn’t “cranked”.

If this is a run of the mill Sansui receiver issue already addressed, can someone steer me to that thread? I've looked around and didn't see this specific problem, although with the many years of postings, it might be in here somewhere. Thanks to all for any assistance you may be able to lend.

Check F04 and F05 by the driver board (check all 4 there while you are in there). I've had the same thing happen. The fuse clips needed squeezed to hold the fuses tighter. Also, if your "version" has fuses on the protection board (some do, some don't), check them as well. If they are fine, put your speakers on the A terminals to see if the speaker switch has gone awry (I doubt it though). If need be, we'll dig deeper. ;-) Also, even if a fuse "looks" good, test it with a meter for continuity. Sometimes they "blow" inside the end cap.

 

[BearsFan]

Skywatcher, I take it that you are referring to the 4 fuses with the white glass? I've been away from the repair world for a long time, since my Navy days! I'd rather pull these with the plastic fuse puller, which I don't have at this moment. Everything looks a bit fragile in there and I'm afraid if i try to pry these out with a screwdriver I may cause more issues than a blow fuse. No point of checking in circuit, I realize I have to pull one side up.
Please verify the picture attached as the driver board.
Thanks,

 

[BearsFan]

My lack of patience got the better of me so I used the "toothpick method" to pry up the fuses. The results are F1 and F2 are both open, F3 and F4 are good, 0 ohms. F5 is a clear glass fuse, the element looks ok, a little stuggle getting that one pulled without a fuse puller. Will try further.

 

[BearsFan]

Skywatcher, btw, I did also move the speaker cables to A and C with the same results as you predicted. Based on both F1 and F2 being open, I would suspect that something failed down line in this circuit, no? Do these fuses support a common circuit downstream? Thanks for your support!

 

[ivandezande]

Skywatcher, btw, I did also move the speaker cables to A and C with the same results as you predicted. Based on both F1 and F2 being open, I would suspect that something failed down line in this circuit, no? Do these fuses support a common circuit downstream? Thanks for your support!

One channel on the amp board is fried.

 

[Skywatcher]

Skywatcher, I take it that you are referring to the 4 fuses with the white glass? I've been away from the repair world for a long time, since my Navy days! I'd rather pull these with the plastic fuse puller, which I don't have at this moment. Everything looks a bit fragile in there and I'm afraid if i try to pry these out with a screwdriver I may cause more issues than a blow fuse. No point of checking in circuit, I realize I have to pull one side up.
Please verify the picture attached as the driver board.
Thanks,

Check the 2 at the bottom of your photo (F04/F05). The "ceramic" type of fuse is "explosion-proof", but I just use fast-blo glass fuses. None have ever "exploded". lol! If you use a small screwdriver to pry the fuses up, wrap it in tape first! And just pry on one end so the fuse flips up, then pull it out. The tops of those diodes (the silver oblong things) are "hot" to the filter capacitors. You don't want to short them to the fuse clips. I always put plastic "zip ties" for "handles" on fuses when replacing them so I can just pull them with no tools needed.

 

[BearsFan]

Thank you, is that the F-2624?

 

[Skywatcher]

Skywatcher, btw, I did also move the speaker cables to A and C with the same results as you predicted. Based on both F1 and F2 being open, I would suspect that something failed down line in this circuit, no? Do these fuses support a common circuit downstream? Thanks for your support!

OK, so that pretty much eliminates the speaker switch as a problem. F01 and F02 are power fuses and if one is blown, replace it with the exact same rating glass (you can see through the glass) fast-blow fuse. If memory serves me right, F01/02 are 10A/250v and F04/05 are 125v rated fuses.

 

[Skywatcher]

Thank you, is that the F-2624?

The F-2624 is the driver board. The board it plugs into, and has the fuses on it, is the power supply board F-2656

 

[BearsFan]

F5 is the glass one that's buried in there. I can see the filament is intact but as you've noted it could be open under the metal cap. I like the zip tie idea! Just to recap (no pun intended), F1 and F2 are blown, F3 and F4 are good. F5 at this moment is unknown, but looks intact, it's a glass fuse. ivandezande, thank you for your feedback as well!

 

[Skywatcher]

My lack of patience got the better of me so I used the "toothpick method" to pry up the fuses. The results are F1 and F2 are both open, F3 and F4 are good, 0 ohms. F5 is a clear glass fuse, the element looks ok, a little stuggle getting that one pulled without a fuse puller. Will try further.

OK, replace the F01/02 with glass fast blow 7A/250v (so it pops quicker if there is a problem). If they pop again, there is a serious problem that needs "surgery". I just checked the schematic and F04/05 can also be 10A/250v fast blow as well though my original F04/05 were 125v rated. NOTE: I highly recommend using a Dim Bulb Tester (DBT) *before* powering it up again! Something can fry before the fuse gets a chance to blow which can cause further damage. We want to avoid that. Also, disconnect your speakers, and anything else first, and have the volume down all the way, selector set to AUX with nothing hooked to it.

 

[Skywatcher]

F5 is the glass one that's buried in there. I can see the filament is intact but as you've noted it could be open under the metal cap. I like the zip tie idea! Just to recap (no pun intended), F1 and F2 are blown, F3 and F4 are good. F5 at this moment is unknown, but looks intact, it's a glass fuse. ivandezande, thank you for your feedback as well!

F01/02 are AC power fuses, F03 (near the front, just behind the tuner section) is a 3A/250v for the lamps, F04/05 are for the F-2624 driver board. Check the fuses to see if they are the right ones. Someone may have put undersized fuses in.

 

[BearsFan]

Thanks Skywatcher! Much appreciated. I need to go out and grab some fuses and that will be tomorrow, so this effort is on hold for a day. Just to keep things coordinated, I did ask this same question from a tech yesterday prior to posting today. One thing he suggested was to remove F3 and F4 for the test first. He noted if F1 and F2 blow in this configuration it is more likely a power supply issue and if they don't it is more likely an output stage issue. Since we are all sharing info to gain knowledge, would you concur with this strategy? Thanks much, I will get back as soon as i have the chance to buy some fuses.
Dan

 

[Skywatcher]

F5 is the glass one that's buried in there. I can see the filament is intact but as you've noted it could be open under the metal cap. I like the zip tie idea! Just to recap (no pun intended), F1 and F2 are blown, F3 and F4 are good. F5 at this moment is unknown, but looks intact, it's a glass fuse. ivandezande, thank you for your feedback as well!

To clarify, F01/02, and F04/05 are the white ones. The glass fuse is F03 and is "snuggled" in a tight spot. It is probably fine.

 

[BearsFan]

Skywatcher, I just reread your last post and I was in error. F1 and F2 are blown, that is correct. F3 is the glass fuse in front and that one is unknown but looks intact. F4 and F5, the other two ceramics are good. I misidentified F3 and prior. Thanks

 

[Skywatcher]

Thanks Skywatcher! Much appreciated. I need to go out and grab some fuses and that will be tomorrow, so this effort is on hold for a day. Just to keep things coordinated, I did ask this same question from a tech yesterday prior to posting today. One thing he suggested was to remove F3 and F4 for the test first. He noted if F1 and F2 blow in this configuration it is more likely a power supply issue and if they don't it is more likely an output stage issue. Since we are all sharing info to gain knowledge, would you concur with this strategy? Thanks much, I will get back as soon as i have the chance to buy some fuses.
Dan

Yes, removing F04/05 is a good approach. Get the schematic so you can trace out where things go if F01 or 02 still blow with 04/05 removed. I would also remove the driver board F-2624.

 

[BearsFan]

I probably should throw together a DBT, this is my first foray into troubleshooting this stuff. I was a Navy avionics tech for 6 years in the 70's and a field service tech for years, but I haven't used these skills for awhile. Since I have about 15 vintage units and i'm retired, maybe it's time to get back in the saddle! My inventory includes 5050, 6060, 8080db, 9090, G7500 and 9090db.
I'm hoping this 9090DB issue can be resolved, time will tell. Thanks again!

 

[BearsFan]

From what I can make out on the schematic, F1 and F2 directly feed SS5, with two filter caps, c12 and c13 on the input to SS5.

 

[Skywatcher]

I probably should throw together a DBT, this is my first foray into troubleshooting this stuff. I was a Navy avionics tech for 6 years in the 70's and a field service tech for years, but I haven't used these skills for awhile. Since I have about 15 vintage units and i'm retired, maybe it's time to get back in the saddle! My inventory includes 5050, 6060, 8080db, 9090, G7500 and 9090db.
I'm hoping this 9090DB issue can be resolved, time will tell. Thanks again!

Yep, time to "rearm" for another "adventure". lol! A DBT and a good DMM will do just fine for most everything here. I also have an Atlas transistor tester, and one of those "cheapie" component testers for "quick" tests, and identifying EBC on transistors. Don't worry, with all the talent around here your 9090db will live again! Your 8080db is (almost) identical so you have a "guide". Also, the Sansui schematic/service manual includes both as well as the 890db and 990db (black faced models).