• Failing Power Supply Capacitors. CRITICAL FAILURE. As of this date, January 23, 2003, this has just started to appear as a possible pattern of failure. A second amplifier with this failure has come to our attention. We recommend that all NPM amplifiers have parts BR40, C40 and C41 replaced with new ones as soon as possible. See below for more information.

  Symptom of Failure: Smoke and damage to the power supply circuit board as shown in the following photographs (courtesy Les Nagy, Sweden)

	Power supply circuit board. Note smoke and heat damage up near the wire harness solder points.
	Damage is all along the left side of the central heat sink.
	Damage is extensive on rear of circuit board.

Cause of Failure. Undetermined. Possibly failed bridge rectifier, BR40 (located center top), due to heat from the rectifier tube; or failed filter capacitors C40/C41.Counterpoint used these capacitors in many products and they have proven reliable in the long run, so overheated BR40 seems the most likely cause.

Repair Options. At this time, we have no idea how to repair this damage. The circuit board is too damaged to repair and we have no replacement boards (the cost to make a new batch is a couple thousand dollars and I will undertake it if this problem becomes common).

Suggested Course of Action: Before the damage occurs, remove the suspected old parts and install new ones. This should give many more years of operation. I would recommend replacing BR40 with a new GBPC606 6A/600V (www.digikey.com, P/N KBPC606-ND), and the capacitors should be replaced with new 6800uF/35V ones, no larger than 22mm diameter, and 10mm lead spacing. A part equivalent to the old part is the Xicon XRL35V6800 (www.mouser.com P/N 140-XRL35V6800-RC, rated at 85 degrees C). A 105 degree C part would probably last longer, but I don't offhand know of one. You might also consider the Nichicon FX 4700uF/35V 18mm, 85C sold by Michael Percy Audio. It may sound better than the Xicon one.

We can do this work here at Alta Vista Audio for $435 for a pair of NPMs (return shipping extra), but a skilled technician should be able to do the work for less. A technician could upgrade the rectifier bridge to four FRED diodes, properly-heatsinked, and the capacitors to better-sounding / high-temperature ones.