B&K 200.5 S2 Power Amp problem - Please help

Hi guys,

I need your help and advice please.

I purchased this power amp on Ebay a few months ago. I just realized the amp is having a problem after I heard my friend's B&K 7250 version II (old model). My power amp, all 5 channels, has had low output. Is that possible that my power amp blows the fuses? If yes, do you know where can I buy them? Since B&K company was taken over by ATI company recently, it's hard to contact them for advice.

I'm really appreciated for all your help & advice.

can you elaborate on your statement - "all 5 channels, has had low output"? do they all have low output at the same time? Is it intermittent? Have they ever produced strong output?

There are a couple of things that could be simple to fix. 1) are the volume pots on the back of the amp turned all the way up? (forgive me for this one - it's just worth asking cause it's the first thing I would check if I had a problem. 2) Fuses blown - B&K uses internal Rail fuses. Their not hard to replace but you have to open the amp up and be comfortable working inside. Also you need to know how exercise safety around high voltage circuits.
I found a document I previously received from B&K showing the fuses used on each of their amps. Below are the spec's for the Ref 200.5:

Reference 200.5
Main(Line) - 15A SB/250V
Rail (internal) - 6A SB/250V
Speaker - 6A SB/250V

I had a 7250ii (200X 5) and a 2500 (60 X 5). They had a slow blow fuse, but when it went, nothing worked. Radio Shack may have one, but I think I got mine from an Automotive shop like Autozone or Checkers.

It sounds like the vloume knobs in the back, but it not are you getting a Hum or buzzing sound as well, it so that could be a ground problem with the RCA inputs, they can get dmg during shipping.

Hope this helps.
According to information on the B&K website, they are working on a solution for warranty repairs, and that owners should contact the following e-mail address for technical support: george@ee-av.com
I appreciate all your information and suggestion.

Bdgregory - Yes they all have a low output at the same time since I purchased them on Ebay. At first, I did not realize it. After I had a chance to listen to my friend's B&K system, I found out something wrong with my amp. My amp does not have the volumne knobs on the back, so I could not do anything else. Can you explain more the fuse number below?

Main(Line) - 15A SB/250V
Rail (internal) - 6A SB/250V
Speaker - 6A SB/250V

If I go to Automotive shop per Briweve's suggestion, what information I should give or ask them? Sorry I'm blind with this.

Briweve - Again, my amp does not have the volumne knobs on the back. I turned the volumne of my pre-amp to 90%, there's no HUM OR BUZZING SOUND from my speakers.

Gbart - I emailed George, but I have not received any reply from him yet. Also I tried to contact the seller and hope he can response back and help me with it.

Thanks again guys!
since you have power you definitely don't need to worry about the main fuse (15 amp), and likewise you have some sound so you don't have to worry about the speaker fuse) The Rail fuse is a 6 amp Slow Blow with 250 volt rating (6A SB/250V)

Here's the fuse you want - they have them at radio shack:
6 amp Slow Blow fuse

How does your amp sound other than it's not loud? If the rail fuses were out, I'm thinking you would have worse problems than low volume. I also wonder of the volume pots are somehow inside your amp.

Did you compare your amp sound to your friends in your system? If not, your perception may also be resulting from your pre/pro setting.
First, all your fuses would appear to be 'good'. You ARE getting output from all 5 channels, right?

Look at the back panel. There will be a balanced / unbalanced switch near each set of inputs. IF you are using RCA connections, make sure it is set to 'unbalanced'.
Turn the level way down...or the system OFF before adjusting this.
I'll bet the last owner used balanced connections and it is so adjusted.

Also, how sensitive are your speakers? I can't believe that is the problem, but it never hurts to ask. This amp should even drive my low-sensitivity panels OK.

I read the instructions:: no level controls inside the amp.
Magfan - You're right. Last night, I changed RCA/XLR switch from XLR to RCA and the output volumne increased. I thought the amp won't have any sound if the switch does not setup correctly. My bad!!!

Anyway, thank you so much guys for all your help and make my life happy now......
For a second there, I though I was unbalanced!

Good for you......

sounds like it should now, right?
If you run a dedicated outlet of 20A breaker and outlet to an Amp that has a 15A fuse, I`m quite sure you will blow the main fuse on the amp due to allowing 20A come through a 15A fuse.
If you run a dedicated outlet of 20A breaker and outlet to an Amp that has a 15A fuse, I`m quite sure you will blow the main fuse on the amp due to allowing 20A come through a 15A fuse.
. . . very funny.
I'm hoping I can re-open this thread as my problem is similar. A B&K 125.7 Amp I used for about 5 years without problems - balanced connections. I boxed it up about a year ago and a friend wanted to buy it so he took it home and set it up. 4 of the 7 channels had low output using unbalanced connections. He tried the switches in both positions, no change.

I went over yesterday and we first took a mono white-noise signal directly into each unbalanced input with a single speaker hooked to that channel and measured the output. Then moved the source and speaker channel by channel and measured them all. Sure enough 4 channels are ~30 db lower - changing the switch on the "good" channels lowers their output by ~30 db, but changing the switch on the "bad" channels does nothing.

Then we did the same test using a preamp with balanced outputs, same results - balanced or unbalanced the same 4 channels are bad. These 4 channels happen to belong to 2 stereo pairs, so of the 7 channels 1 stereo pair is good, and the 1 mono amp is good, 2 stereo amps are bad (the balanced/unbalanced switches work in stereo pairs - the mono amp has it's own).

I took the top off and checked all the fuses on the top of the amp (15 in all). They all seemed good. The sound of the low output channels seems OK, though it was hard to get it loud enough to really evaluate distortion.

Seems that some are familiar with these amps, any other ideas beyond "the switch"? Thanks for your thoughts and any advice.
Well, think I figured it out. Put the amp on my workbench and ran the same test as last night; this time only 2 channels were bad. Started playing with the switches and noticed some noise, sprayed some contact cleaner in and worked the switches several times.

Now all seems well, unbalanced all the inputs produce the same level, pushing the switch in to balanced causes the level to drop ~30db. Running balanced all the channels also the same, letting the switch out to unbalanced actually causes the level to go up a little.

So if anyone else has this problem try cleaning the switches (once you're sure they're in the right position).