Also by shorting pin 8 to pin 7 it seems that the protection switches off and amplifier works. Can the NAD schematic really be right when looking to pin 7? It just goes to ground through capacitor. Totally different from datasheet, where it has only resistance after VCC..
Sorry for constantly posting, just measuring here and reporting withing it
Sorry for constantly posting, just measuring here and reporting withing it
Weird thing here is that NAD service manual says that CB35 is UPC1237 Protection module, but in the CB35 place there is this:
Pins seems to be same as UPC1237 IC. I quess that is just the same thing, but only difference is withing the pin 7 and its resistor. NAD C325BEE seems to be using the original UPC1237 IC and it has the resistor at pin 7.
Anyone know anything about this? Can i change this to UPC1237IC if i add resistor between pin 8 and 7?
Ill can post also picture of front of it, just ran out of camera battery when i tried to move them to computer
An externally hosted image should be here but it was not working when we last tested it.
Pins seems to be same as UPC1237 IC. I quess that is just the same thing, but only difference is withing the pin 7 and its resistor. NAD C325BEE seems to be using the original UPC1237 IC and it has the resistor at pin 7.
Anyone know anything about this? Can i change this to UPC1237IC if i add resistor between pin 8 and 7?
Ill can post also picture of front of it, just ran out of camera battery when i tried to move them to computer
No, you misunderstand. The threshold voltage is the level at which a certain state will change. Below the threshold you get one state, above it the other. In this case the state is whether the relay is switched on or off. Logically, the relay must be switched off in case of a fault.
E.g. if there were too much offset at the output, the level on pin 2 would be either above 0.62 V (typically, the actual value may vary between several ICs but must always be within min - max of the datasheet, in this case 0.54-0.70 V) or below -0.17 V (typ). If that were the case, then the protection module would switch off the relay (or invert its state from on to off).
Since pin 2 measures 0 V, that indicates that there's no offset fault, this is OK.
If pin 1 were above 0.67 V, there would be an overload. This is not the case (0.002 V), so again it's OK.
Pin 3 should be 0 V, so this is OK.
Pin 4 looks odd indeed. If you look at the schematic of the amp, you'll see that it's connected to an AC voltage and D303 will perform half wave rectification. Pin 4's function is to quickly switch off the speaker relay at power down to prevent thumps (see page 4 "Function of AC level detection" of the datasheet).
If the voltage is below 0.74 V, it will switch the relay off. Since -17.75 V is pretty much below the threshold, this must be the reason why the relay won't switch on.
First thing to do would be a diode check of D303 and a resistance measurement of R320 (obviously with power switched off). The diode should measure around 0.5-0.7 V in forward direction and over limit in reverse direction. R320 should be around 22 kOhm (measuring "in circuit" might give slightly different readings but shouldn't be too far off in this case).
If those two check out OK, then the next thing I would do is remove the protection module, power up and measure the voltage on the hole where pin 4 normally is. If the voltage changes from -17.75 V to a positive voltage (I'm guessing about 25-30 VDC), then I would be pretty sure that the proctection module itself is faulty.
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Also by shorting pin 8 to pin 7 it seems that the protection switches off and amplifier works. Can the NAD schematic really be right when looking to pin 7? It just goes to ground through capacitor. Totally different from datasheet, where it has only resistance after VCC..
The power ON mute is there to prevent thumps during power up. The cap and the high resistor (the 56 k resistor seems to be on the protection module in your pic) create a slowly rising voltage on pin 7. When that voltage has reached a threshold, the relay is switched on. This slow action creates a delay that is long enough for the rest of the amp te become stable after power up.
Weird thing here is that NAD service manual says that CB35 is UPC1237 Protection module, but in the CB35 place there is this:
An externally hosted image should be here but it was not working when we last tested it.
Pins seems to be same as UPC1237 IC. I quess that is just the same thing, but only difference is withing the pin 7 and its resistor. NAD C325BEE seems to be using the original UPC1237 IC and it has the resistor at pin 7.
Anyone know anything about this? Can i change this to UPC1237IC if i add resistor between pin 8 and 7?
Ill can post also picture of front of it, just ran out of camera battery when i tried to move them to computer
Interesting pic. No doubt this is a discrete replacement for the UPC1237 that I suspect is obsolete.
What struck me while looking at the solder joints is that they don't look very nice. In fact looking at the resistor marked "472" far right, I can't help but think to see "non-wetting" (i.e. solder hasn't formed a good joint during soldering) but at this angle it's hard to tell. You might want to touch it up with an iron and some solder and see if it works...
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Thanks again for helping.
Measured D303 diode to be 0,906 V, does that mean it is broken?
Also measured the resistor and it was fine, ~22kOhm.
Removed the protection module and took a measurements. Pin 4 did not change polarity, but changed from -17,75 to -29,5. Also pin 8 seems to have now 46,9 V.
Heres new pics of protection module:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I think the camera lies a little bit.. not the best camera for makro shots.
Also look at the pics from front.. why is the pin 4 painted to silver, it looks like it is painted with a marker.. maybe someone else took a look before me.
Added power circuit schematic here:
http://levyhylly.entrada.fi/power_circuit.pdf
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Also capacitor C335 is wrong way compared to upc1237 datasheet.
An externally hosted image should be here but it was not working when we last tested it.
Probably not.
OK, I made an elementary mistake in thinking that pin 4 voltage would become positive because I didn't pay attention to the polarity of D303. Since the cathode is pointing towards the AC voltage, it is correct that the DC voltage on the anode is negative with respect to ground.
The fact that the voltage on pin 8 rises to 46.9 V after removal of the protection module was to be expected, it's a result of Ohm's Law (U=I*R). Because there's no current flowing through R342 anymore, there's no voltage drop across it and the full voltage appears on the other side of the resistor. The same thing is the reason for the voltage on pin 4 going from -17.75 V to -29.5 V.
A warning here: don't put the amp on standby with the protection module removed! The high voltage on Q315 may lead to damage if you put the amp on standby. The circuit around Q315 was designed for approx, 5 V, not nearly 10 times more.
Thanks, this angle gives a better view. I still think that the solder joints look bad. Even with leadfree solder they don't have to look this bad.
The fact that the amp works with the relay switched on manually and the inputs of the protection module seem to indicate no fault, I would still suspect the protection module itself as the cause of the fault.
I would resolder every joint on that board and put it back in the amp to see if that has cured the problem.
Now, if that didn't do the trick, I'm not sure that installing a UPC1237 (if you could find one) would work without some modifications. As you point out, there seem to be some discrepancies between the datasheet and the NAD schematic. This may mean that the replacement discrete module is not entirely equivalent to the UPC1237.
Yes, and D303 also points in the other direction (cathode to AC instead of to pin 4). As I wrote in my previous post, this means that the replacement protection module needs a negative voltage to work and is where it deviates from the UPC1237.
Perhaps reversing polarity on D303 and C335 might be all that's needed to make a UPC1237 work, but I'm not sure that's all the modifications you'll have to do.
Ok, already did :/. No smoke or anything odd happened, need to check the circuit when i get home.
Ill try to solder joints of module later today and try it again. New UPC1237 should arrive in couple of days so i might try to mod circuit for it. I think ill also need 56k resistor between pins 8 and 7 also for it.
The C315BEE service manual has a conflict between the schematic and parts list. The schematic shows the circuit board module you found in the amplifier. The parts list incorrectly lists UPC1237 and as you noted several modifications would be needed to use the UPC1237 in circuit.
There are a number of components that need to be changed to use the UPC1237 and in some cases the component value must be calculated based on the voltages in the C315BEE. To do this right will require a fair amount of work and testing to be sure it was done correctly.
The module is just a discrete circuit with transistors and diodes that should be easy to repair. That would be the much preferred path in my opinion. The NAD C352 and C372 revised service manuals have a schematic for the protection module. It is probably the same module that is in your 315BEE. The schematic will be helpful in repairing the module if you decide to go that route.
You can get the service manuals at ElektroTanya | Service manuals and repair tips for electronics experts. There are several listing for each amplifier. For the C372 choose the entry NAD C-372 SM 2; for the C352 choose NAD C-352 SM.
There are a number of components that need to be changed to use the UPC1237 and in some cases the component value must be calculated based on the voltages in the C315BEE. To do this right will require a fair amount of work and testing to be sure it was done correctly.
The module is just a discrete circuit with transistors and diodes that should be easy to repair. That would be the much preferred path in my opinion. The NAD C352 and C372 revised service manuals have a schematic for the protection module. It is probably the same module that is in your 315BEE. The schematic will be helpful in repairing the module if you decide to go that route.
You can get the service manuals at ElektroTanya | Service manuals and repair tips for electronics experts. There are several listing for each amplifier. For the C372 choose the entry NAD C-372 SM 2; for the C352 choose NAD C-352 SM.
Thanks for replying.
I downloaded the C352 and c372 service manuals, and it seems they have separate upc1237ha ic (opamp symbol at schematics) so not the same as pictures in my earlier posts. Atleast i think so. You can see it right, under the green led (8 pin ic).
If you got the right manuals, the protection module schematic is on page 18 for C352 and page 21 for C372. There is also a description of what components changed from the original UPC1237 circuit. The C352 and C372 were transitional models in which early production used the UPC1237 and later units used the replacement module.
The first page of the C372 manual should be dated November 2006; the C352 manual is January 2007.
The first page of the C372 manual should be dated November 2006; the C352 manual is January 2007.
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I had a look at the modifications in the service manual of the C372SM2 needed for replacing the UPC1237 with the module and I'm pretty sure it's the same for your amp.
It looks like the only modifications you'll need to do to be able to use the original UPC1237 instead of the replacement module are:
- reverse the polarity on D303;
- remove C335 and replace with 4.7uF/50 V, mount new cap reversed polarity;
- insert a 47k or 56k resistor between pin 7 and 8 of the IC (the parts list in manual of the C372SM2 lists R777 as 56k, but the modification instructions say it's 47k, either will probably work fine).
Good luck and let us know if you're successful!
It looks like the only modifications you'll need to do to be able to use the original UPC1237 instead of the replacement module are:
- reverse the polarity on D303;
- remove C335 and replace with 4.7uF/50 V, mount new cap reversed polarity;
- insert a 47k or 56k resistor between pin 7 and 8 of the IC (the parts list in manual of the C372SM2 lists R777 as 56k, but the modification instructions say it's 47k, either will probably work fine).
Good luck and let us know if you're successful!
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Protection module itself is so small that i thought it would be easier doing the mods for UPC1237. IC is still on the way, i expected that it would arrive yesterday but it seems it goes over the weekend.
Thanks for listing the instructions, resistor was a question mark for me.
This "case" was my first time on the forums, and its really nice to see so many helping hands here. I'll let you how this project ends
Thanks for listing the instructions, resistor was a question mark for me.
This "case" was my first time on the forums, and its really nice to see so many helping hands here. I'll let you how this project ends
As an aside:
Looking back at post #28, I realize that the C315BEE must have been designed to take the replacement module from the start, despite its parts list listing the UPC1237 as the protection module.
Added to the absence of modification instructions in the service manual, the absence of traces and mounting holes in the pcb trace-layout for a resistor between pin 7 and 8 is a big giveaway. Same goes for polarity of D303 and polarity and value of C335 in schematics.
But I wonder why NAD didn't design the amp with another off the shelf protection IC in the first place... I can't help but think that manufacturing a discrete replacement module is far more expensive than using an alternative IC.
Perhaps NAD designers didn't pay enough attention to obsolescence warnings from the IC manufacturer and went ahead making new designs using it anyway. The status of a component changing from "Active" to "NRND" (not recommended for new design) is usually the first sign that a manufacturer is going to stop production.
Looking back at post #28, I realize that the C315BEE must have been designed to take the replacement module from the start, despite its parts list listing the UPC1237 as the protection module.
Added to the absence of modification instructions in the service manual, the absence of traces and mounting holes in the pcb trace-layout for a resistor between pin 7 and 8 is a big giveaway. Same goes for polarity of D303 and polarity and value of C335 in schematics.
But I wonder why NAD didn't design the amp with another off the shelf protection IC in the first place... I can't help but think that manufacturing a discrete replacement module is far more expensive than using an alternative IC.
Perhaps NAD designers didn't pay enough attention to obsolescence warnings from the IC manufacturer and went ahead making new designs using it anyway. The status of a component changing from "Active" to "NRND" (not recommended for new design) is usually the first sign that a manufacturer is going to stop production.
Its alive! Got the upc1237 ic at thursday and i installed it with the mods yesterday. Saddly i didnt have 4,7 uF 50V capacitor, so installed 10 uF 60V instead. It seems that cap size affects the time what it takes to pull the relay, with 10 uF it is around 2 seconds. Fast enough to me.
Another problem was found that only left speaker was working. Found that the lead from relay output to speker connector was open. Soldered lead again and got it working. Maybe that was the reason for broken protection circuit?
Anyway, thanks to everyone who helped, especially jitter and Bill_P
Another problem was found that only left speaker was working. Found that the lead from relay output to speker connector was open. Soldered lead again and got it working. Maybe that was the reason for broken protection circuit?
Anyway, thanks to everyone who helped, especially jitter and Bill_P
Good to know that you fixed your amp!
The longer time for the relay to switch on with the 10 uF cap is to be expected as it takes longer for the voltage to reach the threshold than with the 4u7 cap (for the same reason as I explained in post #24).
If you don't mind one more replacement, then you could replace R320 with a 10k resistor. This should shorten the delay and would be closer to the recommended optimum value in the datasheet of the UPC1237 (see fig. 5 on page 6, with ~17 VAC, the optimum value is 10k, and the C372SM2 indeed uses 10k for R787).
But this value isn't very critical, if you don't mind the slightly longer delay at power up, then you can leave your amp as it is now just fine.
Not likely, the protection circuit only drives the actuating coil of the relay. Wether or not the audio signal reaches the speakers, doesn't matter to the protection circuit.
Anyway, thanks to everyone who helped, especially jitter and Bill_P
You're welcome!
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