Trnsfmr
Well-Known Member
Hi all,
I discovered something new today about the 9001. And believe me, I thought I had figured out everything there was to figure out about this receiver. I've worked on so many of these things now, that you could tell me a symptom, and I could most likely tell you the exact part or problem and where it was.
Anyway, this is most likely wrong with every single 9001 ever shipped. It has to do with the 2X power mode. The 9001 has a function where you can get all 4 channels to drive just the two front stereo channels, in bridging mode, which gives you 2X as much power or 120 watts per channel instead of just 60. This is achieved by using a channel to drive each side of the speaker, with the negative side driving out of phase with the + side.
Bridging mode normally works really well, and actually gives you the peak power of 4X what a single channel does. It also doubles the slew rate, and spreads the heat load over the heat sinks for all 4 channels. So, in bridge mode you usually get the sensation of much more power, and effortless drive, and great sound, better than the single ch version.
Well, the 9001 bridge mode never sounded as good as I thought it should. But since the 9001 is about quad, and I, and most of my customers, don't usually run it in that mode, I didn't think much about it.
I had a customer who's unit developed a giant pop when switching to 2X. And then a unit on the bench that we had just recapped, did the same thing. I had to use the scope, pour over the schematics and actually think, to figure it out. Turns out that a cap that feeds the relay that switches to 2X mode has the cap marked backwards on the board. This cap only comes into play in 2X mode, but passes audio to the right channel, and is reverse biased by 8v (installed backwards). It's a 50v cap, and I guess most caps could handle the reverse bias. We just got a new bag of 2.2uf @50v caps in, and I guess they couldn't handle the reverse bias.
Well, a reversed biased cap doesn't sound very good, even if it doesn't fail. Now with that cap put in the right way, the 2X mode really shines. For a stereo receiver, it now sounds as good as the 9090, which to my ears always sounded a little better than the 9001 playing just stereo. Of course the 9001 always beat out the 9090 in quad mode, so I never thought much about it (that's a joke).
Anyway, if you have a 9001, and you care, it's C30 on the f2636 board. That is the board right behind the front panel with the bal and vol controls on it. You can get this board out without removing the front panel, if you remove the faceplate, and the bottom cover. It's tight, but it will come out.
I'd use a new cap. If you ever listen in 2X mode, it's worth the trouble.
IMPORTANT ADDITION TO THIS THREAD, SEE ADDITIONAL POST BELOW
Well, I'm sorry to say, cause I hate this kind of stuff myself, but there are more variables to this problem. I have six 9001's in the shop right now, plus an 8001, which has the same board. The caps appear mounted correctly in one unit, but most of the time wrong, AND the solder mask, the printing on the board, got corrected, I would imagine, on later boards. I wish I could tell you a serial number, after which you can trust the print on the board, but I can't.
So here is the correct way to deal with this. As you look down from above at the board, f2636, C30 should have its positive side toward the BACK of the receiver, negative to the front. With a flashlight, you can check without removing anything but the wooden cabinet. You have to push some wires aside so you can see, but it's relatively easy to do.
You can also change out the cap, if it's wrong, without removing the board. You just need to remove the bottom plate. It's hard to figure out which two pads are the cap, but you can desolder, pull the cap out, and replace it with some forceps or long needle nose.
Sorry to make this even more complicated, and I hope no one got fooled by the changes. This is the right way to deal with it.
I discovered something new today about the 9001. And believe me, I thought I had figured out everything there was to figure out about this receiver. I've worked on so many of these things now, that you could tell me a symptom, and I could most likely tell you the exact part or problem and where it was.
Anyway, this is most likely wrong with every single 9001 ever shipped. It has to do with the 2X power mode. The 9001 has a function where you can get all 4 channels to drive just the two front stereo channels, in bridging mode, which gives you 2X as much power or 120 watts per channel instead of just 60. This is achieved by using a channel to drive each side of the speaker, with the negative side driving out of phase with the + side.
Bridging mode normally works really well, and actually gives you the peak power of 4X what a single channel does. It also doubles the slew rate, and spreads the heat load over the heat sinks for all 4 channels. So, in bridge mode you usually get the sensation of much more power, and effortless drive, and great sound, better than the single ch version.
Well, the 9001 bridge mode never sounded as good as I thought it should. But since the 9001 is about quad, and I, and most of my customers, don't usually run it in that mode, I didn't think much about it.
I had a customer who's unit developed a giant pop when switching to 2X. And then a unit on the bench that we had just recapped, did the same thing. I had to use the scope, pour over the schematics and actually think, to figure it out. Turns out that a cap that feeds the relay that switches to 2X mode has the cap marked backwards on the board. This cap only comes into play in 2X mode, but passes audio to the right channel, and is reverse biased by 8v (installed backwards). It's a 50v cap, and I guess most caps could handle the reverse bias. We just got a new bag of 2.2uf @50v caps in, and I guess they couldn't handle the reverse bias.
Well, a reversed biased cap doesn't sound very good, even if it doesn't fail. Now with that cap put in the right way, the 2X mode really shines. For a stereo receiver, it now sounds as good as the 9090, which to my ears always sounded a little better than the 9001 playing just stereo. Of course the 9001 always beat out the 9090 in quad mode, so I never thought much about it (that's a joke).
Anyway, if you have a 9001, and you care, it's C30 on the f2636 board. That is the board right behind the front panel with the bal and vol controls on it. You can get this board out without removing the front panel, if you remove the faceplate, and the bottom cover. It's tight, but it will come out.
I'd use a new cap. If you ever listen in 2X mode, it's worth the trouble.
IMPORTANT ADDITION TO THIS THREAD, SEE ADDITIONAL POST BELOW
Well, I'm sorry to say, cause I hate this kind of stuff myself, but there are more variables to this problem. I have six 9001's in the shop right now, plus an 8001, which has the same board. The caps appear mounted correctly in one unit, but most of the time wrong, AND the solder mask, the printing on the board, got corrected, I would imagine, on later boards. I wish I could tell you a serial number, after which you can trust the print on the board, but I can't.
So here is the correct way to deal with this. As you look down from above at the board, f2636, C30 should have its positive side toward the BACK of the receiver, negative to the front. With a flashlight, you can check without removing anything but the wooden cabinet. You have to push some wires aside so you can see, but it's relatively easy to do.
You can also change out the cap, if it's wrong, without removing the board. You just need to remove the bottom plate. It's hard to figure out which two pads are the cap, but you can desolder, pull the cap out, and replace it with some forceps or long needle nose.
Sorry to make this even more complicated, and I hope no one got fooled by the changes. This is the right way to deal with it.
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) Actually the 9000 sounds really good, I just don't care too much for the tone controls. (it's the old blame it on the EQ complaint!!)