Akai aa-6600

[mike_ct]

Hi,
First post to the forum.
I have an old akai as-6600 that I inherited from my father. I have had for about 20yrs.

I had it serviced about 15 years ago. From what I see inside they replaced a couple of larger capacitors.

Recently it started blowing the internal 2amp fuses one at a time. It would happen after the music had been on for a 15-30 minute. If I replace the fuse it works again and will run for a month or longer before it happens again. I haven’t figured out a pattern

Currently the phono preamp is not working either.

I am running into a speaker selector the maintains 8ohms. The speakers off of that are all 8ohm

For input I have a 4 input selector running into the AUX channel. A turntable with separate preamp, cd, tape and blue tooth.

I have not found a repair place this is less than an hour from me (southwest ct).

I have a soldering iron and meter... but an extreme novice building guitar pedals from kits. I am will to try this or defer to an expert.

I downloaded the schematic and read a bunch of forum posts, but can’t quite figure out where to start.

Any suggestions on where to start is appreciated or of a place near me that can service it. I am determined to keep this running for a long time but don’t want the solution to be just swapping fuses

Thanks

 

[quiet]

Nice receiver .
Welcome to Ak.

 

[elnaldo]

Welcome to AK.

If you see light blue capacitors labeled "Sanyo", start replacing those capacitors before doing further testing. Those are absolutely non reliable parts, and tracing an intermittent fail while those parts are in the circuit can be very difficult.

It could be that you need a slow blow fuse, capable to hold the inrush current at power up, perhaps a regular fuse goes weaker with each power ON cycle.

Or , some leaky diode or capacitor at the power supply. You could rebuild the power supply rectifiers and regulators, just in case. It's an old unit, it wont hurt to have a rebuilt power supply.

Check the voltage selector, set it to the proper voltage or a bit higher.

 

[mike_ct]

Thanks for the reply. I don’t see Sanyo listed on them, but they are somewhat blue in color. I am comfortable with a soldering iron if anything needs replacement

See the attached photos. I took some close ups of the power supply section.

It is a bit dusty inside, would a good deoxit cleaning help?

I was going to put in new fuses with the cover off to see if anything was heating up too much and can check voltages. Unfortunately I had to order the fuses since no place around here has the slow blow. Should be here today or tomorrow

Thanks

 

[elnaldo]

Everything looks fine. I see that amp uses several 2SC458, a part known to go bad. So, if nothing else develops a fail, if a slow blow fuse doesn't cure the problem, my first suspects wold be any 2SC458 used in the power supply or in the power amp section (after narrowing a bit reading the schematic)

 

[Oldsansui441]

A high bias can also cause excessive current draw, depending on where the fuse/s are in the circuit this could affect these. In any case it is strange it can go for a month before blowing them. Prob a good idea to also rule out any problems with your speakers or speaker selector.

Good call by elnaldo to check for the correct fuse type, standard or delayed (fast or slow).

 

[elnaldo]

I have seen standard fuses glowing red at power ON (amps with large filter capacitors), and finally fail after several power on cycles. Slow blow fuses don't glow that way.

 

[mike_ct]

thanks for the replies. I just received the fuses today. 2amp slo-blo. I will pop them in tonight and test it out.

Where is the bias control on the board? On my tube guitar amp I have a trim pot on the back. I don’t see anything like that here. There are a number of trim pots in the board, but not in the power section if I am reading the spec correctly

Thanks

 

[petehall347]

might be the speaker selector .have seen it happen before

 

[Oldsansui441]

Where is the bias control on the board? On my tube guitar amp I have a trim pot on the back. I don’t see anything like that here

I'm not sure as l have never worked on one of these and l cannot find a service manual. I would imagine it would at least have a trimmer for the bias.

 

[mike_ct]

I will see if I can track down a service manual.

Connect speakers directly (no switch), Popped in 2 new fuses and turned the radio on. Everything is working as expected. Both channels playing for the last 30 minutes.

Nothing feels like it’s getting too hot. Fuses aren’t glowing.

I will keep running it like this for a couple of days before trying back in my stereo setup.

I can replace the 2sc458 as well if that is suggested. Those are easy enough to replace.

Thanks

 

[Oldsansui441]

That is good news. Yes it would be a good idea to get those 2SC458's out of there when you get a chance. I had an Akai AA-6000 of a similar age that l replaced all of these on the (pre/tone amp and EQ amp) and it made a considerable improvement. I also replaced the amplifier input differential pairs.

The 2SC1345's of a similar (outhouse) shape can also be problematic but l am not sure if this unit uses any of these if in fact Akai did at all, Yamaha did though.

 

[mike_ct]

That is good news. Yes it would be a good idea to get those 2SC458's out of there when you get a chance. I had an Akai AA-6000 of a similar age that l replaced all of these on the (pre/tone amp and EQ amp) and it made a considerable improvement. I also replaced the amplifier input differential pairs.
.

Thanks. What would you recommend replacing them with? I think I counted about a dozen on the schematic. The FM board has a few too. My soldering skills are decent so these look pretty easy to replace so worth probably doing all at once.
What parts are you referring to on the input?


I noticed this morning that the right channel took a couple seconds more to warm up than the left. What I mean is the volume was softer for a couple seconds, then they matched.

Thanks for the support. I just finished building floor to ceiling stereo cabinet and this was the focal point... so I need to keep it up and running.

 

[Oldsansui441]

Hi, l would replace the 2SC458's on the power supply (TR802) and the main amp (TR601 & TR602) board with KSC945C (remember the C suffix is for centre collector) and the 2SC458's on the tone amp and EQ amp boards with KSC1845's.

The reason for my thinking here is that the KSC1845 may be slightly lower noise than the KSC945C but the latter is a 100mA part. The (50mA) KSC1845 should be a non issue & better suited in the AF amplification positions on the EQ and tone boards.

The KSC1845's are only available in the one gain option now but the KSC945C's are available in KSC945C (Y) and KSC945C (G), maybe get some of each so you can better match the gain ranking to the 2SC458's after you pull them out and decipher their gain codes.

Don't forget the pinouts are different between the old and new parts. The original 2SC458's are BCE and your replacements will be ECB.

I would leave the ones in the tuner sections as it may move the alignment.

Sounds like you have been busy building your cabinet, the Akai will have a nice home.

 

[mike_ct]

Thanks for the part suggestions. I am going to put together an order for a bunch of each.

In the meantime i will hook up the receiver back with the speaker selector in the cabinet and see what happens.

Here is a pic. All centered around the akai unit. Bottom drawers are vinyl, tapes and cds
Top door has the rack with all of stereo and tv related items with a cooling fan

 

[Oldsansui441]

Your very welcome.

Here is a pic. All centered around the akai unit. Bottom drawers are vinyl, tapes and cds
Top door has the rack with all of stereo and tv related items with a cooling fan

Your cabinet looks fantastic, nice job .

 

[mike_ct]

I put the stereo back in its place. Worked great for a couple of days... then it blew a fuse on one channel. I replaced the fuse and everything worked. Used it for another hour and no issue.

I did notice the receiver was warm to the touch when running. In the space it sits, the stereo has about an inch of clearance about and a few inches to each side. The space behind it does open up to the rest of the cabinet to allow airflow. The top of the cabinet has too small fans that pull air from the bottom and then out.

I think I may need another fan behind the receiver to either pull in air into the cabinet or push air out.

I am ordering the parts suggested above. Does it make sense to replace any others that may be generating more heat because of age?

Open to any suggestions.

Thanks

 

[elnaldo]

I'd check the bias current.

 

[mike_ct]

I'd check the bias current.

Thanks for the suggestion and I also appreciate your feedback earlier in the thread. Definitely replacing the suggested parts.

Where/how do I check the bias? I didn’t see anything in the spec that led me to that.

Thanks

 

[elnaldo]

I'd check the voltage across R615 and R614 (0.56 ohm) , ONLY IF YOU CAN DO IT WITHOUT RISKING THE AMPLIFIER, that means if you have clip probes you can attach safely to both ends of those resistors before powering the amplifier, and then power ON the amp just to take the readings, don't move the probes while the amplifier is energized. And even without power, be careful and don't short anything, proceed like the amp is connected. Large capacitors can hold a charge and burn a transistor if you cause a short circuit with your probes (don't ask me how I know that)

It seems the bias is set at the factory choosing R612 and R610 to get the desired bias current.

If you don't feel confident doing this, let it alone by now. Priority is to keep the amp working.