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Akai am-2200 recurring nightmare!

greenflash

greenflash

Active Member
I've had this unit for some year now and only recently a (quite slow) technician was able to fix it up; previously I would get it back from him and after a while turned on it would start with crackling noises. Worked ok for some two weeks.. And now it's back to that problem..

And after testing it out it seems to be all upon the left channel (took off the left speaker/cable and the right speaker sounds fine). Odd thing is that I cannot isolate the problem with the balance knob.

Anything I can easily look up to have a clue about the problem (swollen part etc)? I'm quite a noob at this, so I guess I'll eventually have to find another tech but wanted to try something first, where possible (contact cleaning, already done).

Thanks team!
 
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Crackling noises usually point to small signal transistors failing, specially the differential pair at the power amp input. If I were your tech, I'd replace them in both channels, specially if they are toshiba 2sa798 or similar.

Open the cover, If your unit uses those 5pin double transistors (being a japanese unit this is possible ), they are probably your problem.
 
Crackling could also be a grounding problem. Usually the amps are grounded through one screw. Often, tightening the screws that connect the channel to the chassis may solve your problem. Better yet is to clean screws with contact cleaner and then tighten. YMMV
 
elnaldo said:
Crackling noises usually point to small signal transistors failing, specially the differential pair at the power amp input. If I were your tech, I'd replace them in both channels, specially if they are toshiba 2sa798 or similar.

Open the cover, If your unit uses those 5pin double transistors (being a japanese unit this is possible ), they are probably your problem.
Click to expand...

Thanks as usual elnaldo. I'll tell the tech about this to see about his reaction.

sregor said:
Crackling could also be a grounding problem. Usually the amps are grounded through one screw. Often, tightening the screws that connect the channel to the chassis may solve your problem. Better yet is to clean screws with contact cleaner and then tighten. YMMV
Click to expand...
Hi sregor, even if the crackling is on one channel only? That's interesting but I lack the skills to even identify the channels itself.. I'll try to find the manual and see, I'm a total noob and in this matter! Thanks a lot.
 
Just make sure to adjust all the screws :) And visually check for those double transistors. If you see them, replace them and try.
 
Here is the service manual : http://www.hifiengine.com/manual_library/akai/am-2200.shtml

After adjusting all the screws, I'd check or replace TR1 and TR 2 at the power amp board, 2SC1570.

A tech can test the bad transistors with a freeze spray. Tell him to freeze the small signal transistors, the bad one will start to do more or less noises in the freeze-warm cycle. You need to spray, and wait while listening. A good transistor won't do more or less noises when frozen.

If you replace them, that pair of transistors need to be hFE matched, to keep the DC offset within specs. Also, I'd measure DC at the output. If those transistors are going bad, for sure the DC went off specs.
 
elnaldo said:
Here is the service manual : http://www.hifiengine.com/manual_library/akai/am-2200.shtml

After adjusting all the screws, I'd check or replace TR1 and TR 2 at the power amp board, 2SC1570.

A tech can test the bad transistors with a freeze spray. Tell him to freeze the small signal transistors, the bad one will start to do more or less noises in the freeze-warm cycle. You need to spray, and wait while listening. A good transistor won't do more or less noises when frozen.

If you replace them, that pair of transistors need to be hFE matched, to keep the DC offset within specs. Also, I'd measure DC at the output. If those transistors are going bad, for sure the DC went off specs.
Click to expand...

Thanks a lot elnaldo! I'll try to grab hold of the guy again and give him this information so to see if he can actually perform a final fix. The amp was working fine for a couple of weeks after I got it from him.. and then all of sudden it started to act up again.. other than that only a penetrating buzz persists when I turn it on, but that's nothing I am really worried about. I had this item for sale online and I had to pause the sale until I figure this out..
 
For reference, I think I found TR1/TR2 thanks to the diagram and your indications.

CfPK7pB.jpeg
 
those are TR1 and TR2 (confirmed with the service manual). I see your unit has 2SC2240, and the manual calls for 2SC1570. Both are low noise transistors, being 2SC2240 of higher voltage, seems to be a production change since I think those transistors are not available down here.

A KSC1845 could be a modern replacement.

BTW, in some opportunity, get rid of those "TRec" Chinese capacitors, fit some quality parts in there when you can. (no hurry, but do it some day)

Also, I see "solder" on some of your fuses, what could mean "repaired" fuses. I'd replace them with the proper sized fuse.
 
Just to update this thread, happened that "greenflash" is a local, living in a near neighborhood (30Km, 20 miles away), we'll solve this issue in person.

Thanks for your help.
 
Hi, greenflash and elnaldo.

I know this is an old post (2 years), but I need your help.

I have the same amp model (Akai AM-2200) with similar problem: left channel crackles first 3-4 minutes playing music. After that, sometimes crackling decreases near zero. My transistors are C1313 and capacitors are the 1977 original Chemi Con (see photo).

Idle current in left channel is over 25mA. In right channel is almost 25mA. Service Manual says optimum is 20mA.

How did you repair your amplifier? Do you remember? Thanks a lot!

(¿Puedo escribir en español en el foro? Mi inglés es muy malo...)
 

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SpiderHi-Fi said:
Hi, greenflash and elnaldo.

I know this is an old post (2 years), but I need your help.

I have the same amp model (Akai AM-2200) with similar problem: left channel crackles first 3-4 minutes playing music. After that, sometimes crackling decreases near zero. My transistors are C1313 and capacitors are the 1977 original Chemi Con (see photo).

Idle current in left channel is over 25mA. In right channel is almost 25mA. Service Manual says optimum is 20mA.

How did you repair your amplifier? Do you remember? Thanks a lot!

(¿Puedo escribir en español en el foro? Mi inglés es muy malo...)
Click to expand...
Hello.You can send me a private message in spanish, I think keeping the forum in just one language will be better.

I'm sending you a private message with the detail of the work done in this amplifier.

I remember the main probem was a transistor installed incorrectly in the previous repair (I think an NPN instead of a PNP, or a transistor backwards) causing an oscillation.
 
Well. Job done. :thumbsup:

First of all, many thanks to :bowdown: Elnaldo, without whose help and advice, I would not have been able to fix the amplifier.
This is a little journal of my work. I hope it can be of help to other people.

-Replaced in L-R channels the 2x2SC1313 transistors of input differential pair with 2xKSC1845:
* hFE=405-388 (Left channel)
* hFE=396-396 (Right channel)
* Note: originals Aug-1977 2SC1313 in no-problemo channel, hFE > 600: DC offset=0.5-3mV (OMFG!!!) after 10 min. power ON.
-Replaced all light blue Sanyo OSCON coupling capacitors in pre and main board with 1uF 50V Panasonic FC (low ESR, not low leakage as Elnaldo and Service Manual recommends).
-Replaced all 2SC1571 in pre board with 2KSC1845 (hFE=384 to 386). Yes. Definitely, amp sounds now better (yeah!). :rockon:
-Re-replaced Panasonic FC coupling caps with better Nichicon UKL (low leakage) 1uF 100V. After that, maybe amp sounds smoother. Maybe. I think. But not sure at all.
-Full recap with Nichicon UFW capacitors. Same capacitance and greater voltage.
-BIAS current adjusted to 20-23mA, as Service Manuals recommends.
-DC offset with all pots=0:
* Room @22ºC.
* After 5s: Left=16-17mV. Right=23-24mV.
* After 10m: Left=13mV. Right=18mV.
* After 45m: Left=9 mV. Right=13mV. (but Vol=15%)

Well, service is done. Results? For me, a VERY decent amp :music:, with warm, good basses and regular mid and high tones. Although with a low 50Hz hum noise. o_O

I know for many AK'ers (with recaps of +100 items) that is a child's play. But for me, it was the first serious electronic work in 30 years. And I'm very proud of it. :)

DSCN2125.jpg
 
SpiderHi-Fi said:
Well. Job done. :thumbsup:

First of all, many thanks to :bowdown: Elnaldo, without whose help and advice, I would not have been able to fix the amplifier.
This is a little journal of my work. I hope it can be of help to other people.

View attachment 1290743
Click to expand...

Excellent! congrats. Yeah a tiny little marvel. In the end I took the amp to @elnaldo and he did a great job to bring it back alive. Sold it years ago but it did sound great, enjoy!
 
SpiderHi-Fi said:
I quote myself:

Discovered that is NOT hum noise from PS, but static/RF noise. Solved connecting chassis to Mother Earth. :)
Click to expand...

Oh that's the issue in a lot of occasions.. I had that problem with the amp I connect to my computer. Tried a few, my Yamaha is currently a success lol no humming (or very low) I did use some grounding but still, others wouldn't stop the noise even with earth connected (granted, not the best grounding ever!)
 
Hello; I've been restauring this amp for a few days;
- every caps have been replaced
- transistors 2SC1313 on Main Amp P.C Board were changed with KSC1845.
- transistors 2SB560 on Main Amp P.C Board were changed with KSA916YTA
- transistors 2SD438 on Main Amp P.C Board were changed with KSC2316YTA
- transistors 2sc1571 on Tone Control P.C Board were changed with KSC1845.
I'm also getting a hum; not sure if it is caused by my transistors subsitutions. What exactly did you mean by "connecting chassis to mother earth" ?

Thanks for helping me !
 
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