NAD C325BEE Amplifier - Are these capacitors leaking, see photo ?? - Page 1
Forum section: electronics / repair

author: SimonCantrell
author_rank: Newbie
timestamp: January 04, 2024, 04:42:04 pm
content: Hello, thanks for looking at my question, are the capacitors in the photos leaking?Possibly this is why my NAD C325BEE amplifier won't turn on. The amplifier saw little use and was then in it's box in the spare room for the last ten years. I unboxed it and plugged it in but now I just get an orange standby light and it won't power on. I can replace a few components myself but more than that I'll need to send it off for repair. So far I've looked at the Service Manual, read some discussions (here) and tested power supply voltages. Thanks for any advice on these capacitors, Simon

author: RoGeorge
author_rank: Super Contributor
timestamp: January 04, 2024, 04:48:49 pm
content: That's a rubbery glue, used to dampen vibrations.

author: SimonCantrell
author_rank: Newbie
timestamp: January 04, 2024, 06:26:16 pm
content: Thanks, so it's not that then!I measured the output voltages on the power supply board, where the cable goes to the main circuit board, what is marked as +37 gives only 31.5v and what is marked as -37 gives a reading of -40. Is this normal, or should it give the correct voltages even when the device is in standby?? I was hoping the capacitors were the problem, I'm interested but not very experienced with electronics, so unless the problem is 'obvious' I'll have to get someone professional to look at it. Thanks again, Simon

author: GLouie
author_rank: Regular Contributor
timestamp: January 04, 2024, 08:17:28 pm
content: I don't know the device, but your voltages certainly seem out of spec. Also, your capacitors could still be faulty with no outward sign, despite glue being on the outside.

author: FIXITNOW2003
author_rank: Regular Contributor
timestamp: January 05, 2024, 07:42:32 am
content: these are the caps i replaced on the one i repaired"C110, C111,C210,C211 where completely open, C203 and C204.SMD caps where completely shot too"

author: RoGeorge
author_rank: Super Contributor
timestamp: January 05, 2024, 08:33:26 am
content: Quote from: SimonCantrell on January 04, 2024, 06:26:16 pmHard to draw that conclusion from the pics.- Sometimes a capacitor may leak, and you'll see some sort of wet/oily/acid electrolyte spilled under the capacitor. If the spill was long ago, the wet electrolyte spill might turn into white matte. This is rather rare to see.- more common is when the metallic can of the capacitor bulges on top, where the dents in the can were made (to release pressure in the eventuality gases are formed inside a capacitor - if vented, must be replaced), your caps don't look bulged at all- another common failure is when the electrolyte dries out, and the capacity is drastically reduced. This happens first for capacitors near heat sources (placed on the PCB near a power resistor, or near an Al radiator of another component that runs hot. That's easy to check by removing the capacitor and measuring its capacitance.- there is another type of failure seen in switching power supplies mostly (SMPS), when a capacitor doesn't leak, doesn't bulge, and the capacitance measure OK, yet it has developed a high ESR (Equivalent Series Resistor). Typical audio amplifiers don't make use of SMPS, but I don't know the model you are trying to fix. For other PC or more recent TV/monitors where the power supply is of SMPS type, a test against high ESR caps is by heating the capacitor at 30-50*C or so (with hot air) then powering the device again and observe if it starts working. At higher temperature, the ESR goes down, and often this is enough to make the device run normally again, but at soon as it cools down, the ESR raises back and the device fails to work.

author: SimonCantrell
author_rank: Newbie
timestamp: January 05, 2024, 01:57:31 pm
content: Thanks for the replies, they are really useful. Despite my lack of electronics experience I would love repair this amp myself. I measured he power supply voltages which seem off. The larger wires direct to the transistors give the correct voltages. The smaller power cable to the main board seems to be wrong, If I measure between the 0v pin and +37 and -37, I get +31.5 and -40 respectively. However if I measure between the large GND (for negative for the transistors) then I get +37 and -37 volts. Does this suggest a fault.... or am I not understanding this at all. I´ve attached the circuit diagram with the points I measured. Thanks again for any advice, Simon

author: RoGeorge
author_rank: Super Contributor
timestamp: January 05, 2024, 02:19:40 pm
content: That 0V most probably comes in pair with the next pin near it (marked 8VAC), so it is probably an 8V alternative between 0V and 8VAC pins, and unrelated with the +/-37V. I would expect to measure 8Vac between 0V and 8VAC pins, with the DMM set on Vac measurement (but I can't say for sure that's the meaning of those pins).The correct way to measure the +/-37V is relative to GND, like you marked in green.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 05, 2024, 02:57:28 pm
content: I see in the service manual a debugging flowchart. Have you tried to follow the directions there? Where did the flowchart leads in your case?There is a block called "protection" in the schematics, which might prevent the amplifier to turn on. Do you have all properly connected, with the speakers attached correctly, no short circuits, etc.?Have you tried turning it on from the remote (maybe the front panel button got oxidized after 10 years in storage, and now it doesn't make contact when pressed)?

author: tunk
author_rank: Super Contributor
timestamp: January 05, 2024, 03:39:16 pm
content: IIRC, some of these glues can by age turn (slightly) conductiveand cause problems. I guess you can test it with a multimeter.

author: SimonCantrell
author_rank: Newbie
timestamp: January 07, 2024, 08:39:44 am
content: Thanks to everyone for the replies. The comment about the Protection reminds me about a possibly relevant fault the amplifier has had since it was new. From when it was new, after listening to music (not loud) for about 45 minutes, the music would cut out for a second and I would hear a relay click in both directions and the music would resume as normal. I returned the amplifier for repair but it was returned to me 'no fault found'. I just lived with it like this, could that have been the protection circuit inadvertently activating?? The Power switch does mechanically create a circuit when pressed, I tested this. I think, although I obviously wasn't paying attention to it, that when I turned it on the first time a few days ago that the light above CD was very briefly lit, maybe it worked for a few seconds. I'll start studying the protection circuit diagrams, and see if I can find anything wrong there. Thanks again, Simon