A21 did just die.....

[Loffen]

Did just take a level calibration on the subwoofers in my system and did find out that one of the A21's was dead....

So I took then usuall check on it, it has a input signal (No sound on either RCA or XLR, stereo or biamp ), all connections are good, it has power, all lamps are normal, the relay is clicking, the fuse is ok.

What is wrong ?

Need some help here.......

[Peter Nielsen]

Open up the top cover and check the internal fuses.

[Chris D]

Bummer.

I don't know if I mentioned, but one of my A21 channels just started going out after 6-7 years of ownership. I only noticed it because it started sounding like my front soundfield was really pulled to the right. I checked into it, and one side was definitely quieter than the other. Doing a re-cal, I had to bump up the quiet side by like +10db to match. But then after I'd warmed up the system, all of a sudden it'd kick into full volume, and the left side would then be +10db louder.

So I'm sending in the A21 for service, for the Parasound bubbas to look at.

[Mike_Schmidt]

I wonder about my left channel and thought it was always the recording being left channel dominate. The left is louder than the right and always blamed it on room acoustics since my room is small. Hmm maybe it isnt just me

[Chris D]

One way to find out... do an autocalibration, or check with a SPL meter.

[Loffen]

Ok I have just checked the internal fuses....

All four of them are blown.. How could this happend ??

I am running a total of 8 amps at the moment and this A21 is used for the side surrounds, the system was powered up for the first time in about a week and there was nothing wrong after the last time it was used...

Should I just replace the fuses and give it a try or is there anything else I should check first ?

[Glen B]

I would contact Parasound before attempting to replace any internal fuses. These are rail fuses that may likely have blown to protect the amp due to a part(s) failure. If you replace the fuses and apply power without diagnosing the cause, there is the possibility that you may do more extensive damage.

[Chris D]

The same thing happened on my New Classic amps. On Parasound's instruction, I replaced the internal fuses, and as soon as I plugged them back in and turned them on, they blew again. Sent them to Parasound for service. Got fixed, but I can't remember what they ended up saying the root cause was.

[Peter Nielsen]

True about the internal fuses. Normally they should not blow.... However, checking them does not do any damage! :T

Chris: Interesting story about Parasound asking you to replace the internal fuses. At least that shows I was not out of line suggesting this... :B

Apparently you guys don't remember that Loffen is in Norway and cannot enjoy the services of Parasound USA. He's at the mercy of the Norway Parasound distributor or his local electronics expert...

Loffen: If all the fuses are blown, you probably have a defect output transistor. I'm sorry to say that your amp needs professional care. (Don't let just anybody service the amp. You need to get a MATCHED output device in order to maintain the low noise specification of the amp).

Out of curiosity: How was this amp installed? Did your installation meet the 15cm X 7.5cm X 7.5cm Parasound cooling requirements?

[Glen B]

Well, if you have blown output transistors, when you replace fuses and apply full AC line power, you always stand the chance of extending existing damage to include blown driver transistors, blown bias transistor, burnt emitter resistors, and possible heat damage to the adjacent circuit board.

The proper and safe procedure for energizing an amp with suspected blown output devices is to slowly raise AC line voltage from 0V with a variac while monitoring current draw. A sudden increase in current while doing this would indicate the existence of possible shorted outputs, while at the same time not subjecting the amp to full line voltage.

The main goal of output device gain matching is longterm reliability, by ensuring that load current is shared equally between paralleled transistors.

[Loffen]

Well as Peter did say so do I live in Norway and I guess it is not so easy to get it repaird here as in the USA, sure we can get it repaird but we do not have the 10 year warranty so it will cost you an arm, maybe a leg to...

I bought this unit new from a Norwegian dealer and I have used it for the last 6 years without any problems.

It does not have the space requierments set by Parasound, it is placed in a rack cabinet as unit # 3 from the top in the picture (unit #4 is now a A21 not a A52 and a A23 is comming in for the center speaker. The 4 other amps in the bottom are JBL Synthesis S800 for the subwoofers, the EQ has been placed in another cabinet)
However so does this cabinet have a pretty good circulation through a remote fan, the temperature at the top of the cabinet does never go over 40 degrees celsius.

But since it is a hassle for me to send it in for service I did replace the fuses last night and turned it on, no problems at all, both channels working and they had the same sound level, there was also no signs of anything getting hot or being burnt, so I really do not know...

I think I will use it for a couple of days and see what happends, if the fuses blows again I will have to send it in but..

[Peter Nielsen]

But since it is a hassle for me to send it in for service I did replace the fuses last night and turned it on, no problems at all, both channels working and they had the same sound level, there was also no signs of anything getting hot or being burnt, so I really do not know...

Great! :T :T :T

Obviously no components are damaged. My gut react is that you may possibly have bad solder joints. If you have a friend that knows electronics/servicing, you might want him to go over the solder joints for the big electrolytics and output transistors and resolder as necessary. This should be perfectly safe and is a good procedure to do on any of the Parasound amps if it has not been done before...