CJ repair in San Jose

[dravid1]

Hi All,
My MF2550 has topped working (distorting the sound , popping etc).
I was wondering if anyone could recommend a good service center / Technician in San Jose CA to take a look at it. IF not i guess I will have to send to VA.
thanks

[admin]

First, welcome to CJO. Nice to have you with us.

Unfortunately, I don't know any service center in your area. Have you opened her up to look for any signs of damage or component failure? Is it both channels or one? Is there anything you can do to elicit these sounds or are they random?

[dravid1]

Hi,
Thanks for getting back on this
I have not opened her up but did notice a slight burning smell when it first started having the issue.
The sequence of events was as follows
After powering up both the preamp (ACT2) and the MF2550, I switched the source using the remote of the ACT2 and that led a loud boom on both speakers I believe but cant be sure.
After that I noticed that with levels of input to the AMP around 40 on the ACT2 the output from the amp was very low. I then bypassed the preamp and used a streamer (Linn Akurate) as the source to the amp controlling the output level of the Linn from my computer. At very low levels the sound was OK (not loud but not distorted). However as soon as I tried raising the volume from the computer the output from the AMP started getting distorted with crackles and noise.
I listened to the MAIN outputs both Main 1 and Main 2 through headphones and they were fine. I was using main 1 to drive the AMP.
I also connected main 1 from the ACT2 to an integrated AMP (A Prima Luna Prologue 1) and the sound was fine.
Any suggestions would be appreciated

[AnotherJohnson]

Have you checked the fuse(s) on the amp?
From the manual -

Fuses: The output stages are protected by 4 fuses one on the positive and negative power supplies to each channel. These fuses are located on the bottom of the main printed circuit board. Be sure to disconnect the amplifier from the ac mains power (wall outlet) before removing the bottom cover. Never replace a fuse with a value or type different from that originally supplied by the factory. These B+/B- “rail” fuses are 3AG type 6 Amp Fast Blow. In the event of a fuse blowing repeatedly, contact your dealer or the conrad-johnson service department.

[admin]

As above, I would check the fuses first. Also, at a minimum I would do a thorough visual inspection of the internal components. Look for any burn marks, bulging caps, and check the solder points. It may be a relatively easy fix, you never know.

[AnotherJohnson]

What source were you on before you switched?

What did you switch to?

Variable output or fixed? Line level? Did the source you switched to “ always work before?” Or was it new to your system?

If the fuses were correct, they should have protected the amp. The fact that the boom came with the source change is important. The burned smell is worrisome. Maybe a short and improper fuses? I had a second hand MV series amp years ago and the prior owner had re-fused it with very heavy fuses, giving it no protection at all. I was lucky to notice the drone and glow of a failing power tube, and got to the wall to pull the plug on it before anything was destroyed by the failure.

As admin suggests, look for burned resistors when you’ve got it open. If fuses weren’t correct, resisters can become unintended fuses. Bulging or leaking caps usually come along more slowly due to age related failure. This was quite sudden. And the 2550s are so young, it’s hard to think a capacitor might have aged out. The self protection in my old 2550SE saved it from a similar fate, but it did not save my speakers. I blew up my Thiel CS2s on a transient that resulted from pulling a power cord for a source OUT of a socket that was at a different ground. The 2550SE shut itself down, and restarted fine. But the Thiels were Toast.

[dravid1]

Hi all
Thanks for the advice. I will check the fuses. As for the other questions.
1. I switched from the Phooo (connected to TEA2) to CD (connected to Linn Akurate)
2. No new components and all have been working fine for 3 years or so.
3. Unbalanced outputs from the linn

[Big Dog RJ]

Yep, definitely sounds like a fuse problem.
Low levels in output, distorted sound, dull transients... those are symptoms of blown fuses. As AJ advised, check the fuses immediately and replace with a correct type. You can order these fuses through CJ as they stock a good inventory of such parts and consumables. I would also just keep a few spares on hand in any case, you never know when required.

Hope all goes well soon. Let us know the updates because others can get to know what to do when such things happen.
Best, RJ

[dravid1]

Will do!! Thanks again for all the help

[roberto]

Hola dravid1,

This sentence from you is what I do not like, it makes me to have caution...After powering up both the preamp (ACT2) and the MF2550, I switched the source using the remote of the ACT2 and that led a loud boom on both speakers I believe but cant be sure...

That's a heavy and big transient. What caused this? From where it did come? Is there a burned component?

Please, do a very exaustive inspection inside the amp and search for a possible smoked resistors. If this is the case, don't use the amp until is repaired.

What you did experiment is not a normal behaviour of your system, so be careful.

Happy listening!

[dravid1]

Thanks Roberto
Yes the "boom" by the switching didn't sound good to me either.
Will proceed with caution

[Big Dog RJ]

Well noted there Robbo!

Infact I missed that point completely. Long ago I experienced a similar loud pop when switching sources and muting on the remote of the PFR preamp. It turned out to be DC off-set. Hence, all caps had to replaced in the PFR and that DC offset fed directly back into the big 400w Manley monoblocks, that was a very loud pop! Surprisingly the speakers, Infinity's IRS 1B, didn't break or anything, rather handled that massive pop with ease.

So maybe it's not a fuse or could be DC offset... could be a number of things but I'm sure it's fixable. I reckon have the preamp checked as well, just to make sure the ACT2 is behaving.

Best, RJ

[dravid1]

Just a quick update all. I spoke to Jeff at CJ and he is also leaning towards the fuses being blown. I have ordered the replacements and will post once I replace them.

[Big Dog RJ]

Ah, that's definitely a good thing. Especially if you've talked to the legend himself, JF then you're in good hands. Not to worry, I'm sure you'll be listening to some fine tunes very soon!
Cheers mate,
RJ

[dravid1]

Thanks RJ! The wait is killing me:)

[dravid1]

All
A quick update. Replaced the fuses. It was very easy to so so.
Just as an FYI so it may help others in the future - The bottom plate has to be removed. there are 18 screws that have to be removed and once you do that the plate comes right off.you can see the fuses immediately. There are four of them two for each Channel.swap them out and you're good to go.
thanks for all the support

[Big Dog RJ]

Excellent!
Nice one mate, that was a good clean and easy fix. Also good to have a few spare fuses just in case...

Any chance JF mentioned as to why these main output fuses would have blown? Was it an AC current / voltage surge of some sorts... or something else in the mains power line?

Glad you were able to sort it out, and now you're enjoying those fine tunes!
Cheers, RJ

[AnotherJohnson]

Any chance JF mentioned as to why these main output fuses would have blown? Was it an AC current / voltage surge of some sorts... or something else in the mains power line?

JF is smarter about this stuff than I am, but an easy speculation is a ground difference since everything but the amp appears to have continued to work.

JF is pretty consistent in his view that everything needs to be grounded at the same point.

When he and I discussed this when I was sorting out my LP275Ms, I had already wired the room so that all the audio circuits were grounded to the same ground bar in the breaker box, but he wanted me to go further and ground all the audio components at the same duplex outlet.

I thought he was nuts, but I did what he suggested, and it solved the problem.

When my 2550SE blew my Thiel CS2s, it happened when a source was unplugged from a duplex. Very strange, but it still occurred.

I’m obsessive now when it comes to moving anything. Everything gets shut down. No more messing with one source while listening to another.

On the bright side, the failure of the Thiels opened the door to a speaker search. I’m very pleased with my current set up in that room.

[dravid1]

Jeff felt it might be a transient but not much more. I have all the components on the same ground and now will follow the advice to power down and then switch sources.

[Big Dog RJ]

Yes, that's definitely the best approach. Indeed power down and change things, I even do that if and when swapping interconnect cables even though the source gear is off. Better to be safe than sorry, so I power off everything including all amplifiers before changing over any cables. Have certainly had my share of disasters...

I've come across quite a few dealer personnel who change cables willy nilly, during demos whiles things are fully powered up, including power amplifiers...! Uh oh

Thanks for that info AJ.

Hey Admin, was wondering if you could place AJ's reply under the technical tab, would be very useful for future reference.

Cheers maties, and enjoy those fine tunes Dravid1!
RJ