Kicking off my AU-999 Project.

DCinDC said:
Clean your bias pots.

yep that's the PS caps charging up

Set bias to minimum, then power up without DBT and set bias.
Click to expand...

Perfect DC, thats just what I need to know. Now to find some contact cleaner.

Thank you very much.

George.
 
When mine went dim/bright it was the bias jumping all over the place. The transistor with the long legs was the one at fault...it was open. It burnt up when I mixed up the polarities on a couple of my transistors.
 
tobyj17 said:
When mine went dim/bright it was the bias jumping all over the place. The transistor with the long legs was the one at fault...it was open. It burnt up when I mixed up the polarities on a couple of my transistors.
Click to expand...

Hello Toby,

I got mine to power up with no bright light, but when I went to messing with the bias pot, it got bright and dim as I adjusted the pot.

Just got it cleaned. If that does not do it, I have an extra 1K pot to put in there that is multi turn. I may just do that anyway.

I have been using your thread as a go by since mine was acting similar but did see that there was a transistor mix up on your board.

George.
 
All right, bias set on both channels, but have to leave for a little while. I'll have to try it out when I get back in.

Cool beans. :D

I'll return later with a report.

George.
 
GeoKost said:
I saw where VR803 was in backward, so re did it, set to anti-clockwise, and now I am getting no bright light. I did get bright and dim and jumping around when I messed with bias adjust, so I stopped.
George.
Click to expand...

Now look what happens overnight when I go to sleep.....:yikes:

I was just looking over those pics again George and I was going to ask about that trimmer, because it did look like it was in backwards......and if you had it turned down and in backwards, that would make the bias run away....

Now, whenever I fire up an amplifier after working on it, I have my meters clipped on to an emitter resistor on each channel so I can see whats going on as it fires up......

Looks like you got some good help while I was sleeping in any case....:thmbsp:

If a trimmer goes intermittent on me at all like that I replace it, in my opinion theres a chance the carbon track could be damaged and the problem may appear again at the worst possible time and take your amplifier down......

Looking forward to hear your report.......
 
kevzep said:
Now look what happens overnight when I go to sleep.....:yikes:

I was just looking over those pics again George and I was going to ask about that trimmer, because it did look like it was in backwards......and if you had it turned down and in backwards, that would make the bias run away....

Now, whenever I fire up an amplifier after working on it, I have my meters clipped on to an emitter resistor on each channel so I can see whats going on as it fires up......

Looks like you got some good help while I was sleeping in any case....:thmbsp:

If a trimmer goes intermittent on me at all like that I replace it, in my opinion theres a chance the carbon track could be damaged and the problem may appear again at the worst possible time and take your amplifier down......

Looking forward to hear your report.......
Click to expand...

Ok, after reading your information here, I went ahead and changed the trimmer out and readjusted the bias this morning. Did not have time to check anything out.

Came home for a minute and plugged my MacBook Pro in the Aux via the speaker out of the Mac..... nothing, nada.

Unplugged Mac, touching audio input terminals and get hum out of L and R channels through the speakers, I say thats a good sign, I think.

Have to run back to work and play again later.

Does the Mac speaker output not have enough to drive this amp?

Thanks for checking on this Kevin.

George.
 
GeoKost said:
Ok, after reading your information here, I went ahead and changed the trimmer out and readjusted the bias this morning. Did not have time to check anything out.

Came home for a minute and plugged my MacBook Pro in the Aux via the speaker out of the Mac..... nothing, nada.

Unplugged Mac, touching audio input terminals and get hum out of L and R channels through the speakers, I say thats a good sign, I think.

Have to run back to work and play again later.

Does the Mac speaker output not have enough to drive this amp?

Thanks for checking on this Kevin.

George.
Click to expand...

Oh yes, theres plenty of level available from the macbook to drive the amp.....That should not be a problem....

Plugged into AUX, tape monitors set to SOURCE....

BALANCE check OFF.....

Some AU999's need the pre-out, main-in.......check that, or just use an RCA to RCA cable to connect them together.....

DC offset and Bias set OK? If it did the amp is most likely working.....
Sounds like it just isnt making it through the pre-amp.....
 
kevzep said:
Oh yes, theres plenty of level available from the macbook to drive the amp.....That should not be a problem....

Plugged into AUX, tape monitors set to SOURCE....

BALANCE check OFF.....

Some AU999's need the pre-out, main-in.......check that, or just use an RCA to RCA cable to connect them together.....

DC offset and Bias set OK? If it did the amp is most likely working.....
Sounds like it just isnt making it through the pre-amp.....
Click to expand...

I admit, I have not checked the DC offset.

I am plugged into AUX, tape monitors are set to Source, Balance check is Off. On the back panel, it has the pre to main jumpers in place.

Thanks for your time helping me on this Kevin, I will dig in and check on setting the DC offset.

I shall return.

George.
 
GeoKost said:
I admit, I have not checked the DC offset.

I am plugged into AUX, tape monitors are set to Source, Balance check is Off. On the back panel, it has the pre to main jumpers in place.

Thanks for your time helping me on this Kevin, I will dig in and check on setting the DC offset.

I shall return.

George.
Click to expand...

DC offset, turn amp on leave it on for about 5mins....
Attach your DMM to say the left speaker output, set it to read Millivolts....It will probably have a 0-200mV scale....
Adjust VR801 on the left driver board (which is the other trimmer, not the bias trimmer) to read as close to 0mV as possible, you might get it somewhere between 0mV- 5mV which is OK......0mV is a perfect world, we all know this does not exist....:D
Use small increments, its a sensitive adjustment....
Move to the right channel and repeat......

You could try connecting the Macbook directly to the Power amp in.....MAKE SURE THE VOLUME IS AT MINIMUM on the computer, then bring it up slowly.....I would be surprised if this doesnt get you some audio.....
Do not plug into those inputs with the amplifier on, connect it up with the amp off.....

Let us know how you get on.....:thmbsp:
 
kevzep said:
DC offset, turn amp on leave it on for about 5mins....
Attach your DMM to say the left speaker output, set it to read Millivolts....It will probably have a 0-200mV scale....
Adjust VR801 on the left driver board (which is the other trimmer, not the bias trimmer) to read as close to 0mV as possible, you might get it somewhere between 0mV- 5mV which is OK......0mV is a perfect world, we all know this does not exist....:D
Use small increments, its a sensitive adjustment....
Move to the right channel and repeat......

You could try connecting the Macbook directly to the Power amp in.....MAKE SURE THE VOLUME IS AT MINIMUM on the computer, then bring it up slowly.....I would be surprised if this doesnt get you some audio.....
Do not plug into those inputs with the amplifier on, connect it up with the amp off.....

Let us know how you get on.....:thmbsp:
Click to expand...

All I can say is !!!WOW!!!

Pilot error, I had volume up all the way in iTunes on the screen, but did not have the volume up on the Mac itself.

Drives my Klipsch Icon KB-15's very nicely.

Dang. Wow. Makes you feel good when you get something like this accomplished. :D

Kevin, Toby, Cris, DC, John, hope I did not miss anyone, thank you very much for your help and guidance.

Wow... :thmbsp:

George.
 
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GeoKost said:
All I can say is !!!WOW!!!

Pilot error, I had volume up all the way in iTunes on the screen, but did not have the volume up on the Mac itself.

Drives my Klipsch Icon KB-15's very nicely.

Dang. Wow. Makes you feel good when you get something like this accomplished. :D

Kevin, Toby, Cris, DC, John, hope I did not miss anyone, thank you very much for your help and guidance.

Wow... :thmbsp:

George.
Click to expand...

Wait until you do the pre-amp mod, it will take you to the moon.....:thmbsp:

You must be pleased to hear it running!!

Nice one....well done!!
 
Parts list information.

I also posted this information as an edit in my first post.

Here is a rundown on items I ordered and used. All came from Mouser, except for the 2 power supply caps, which you can get from Michael Percy Audio.

Home made Dim Bulb Tester.

4 Output transistors, MJ21194,
1 20 amp, 200v bridge rectifier.
2 10,000uf 80v caps Nichicon KG Gold.
2 1k ohm, trim pot variable resistors, multi turn. These come in very handy when you begin to set your bias.

For the F1228-1 Head Amp board
4 ZTX795A transistors
2 10uf, 25v caps
2 33uf, 6.3v caps
2 47uf, 10v caps
1 33uf 50v cap
2 BC337 transistors. I did not replace these as Mouser did not have them.

F1277 Minus Ripple Board
1 100uf, 50v cap
1 4.7uf, 50v cap
1 KSA1220A transistor

F1231 Plus Ripple Board
1 100uf, 50v cap
1 4.7uf, 50v cap
1 KSC2609A transistor

F1159 Driver Block Board, amounts for 2 boards.
2 KSA1220A transistors
6 KSC2609A transistors
4 ZTX795A transistors
2 47uf, 10v Bipolar caps
2 100uf, 25v caps
2 1N4148 diodes
2 ½ watt, 15 ohm metal film resistors

F1230 Ripple Filter Block Board
3 220uf, 50v caps
2 100uf, 50v caps

F1209 Tone Control Board, amounts for 2 boards.
6 ZTX795A transistors
2 33uf, 25v caps
4 47uf, 10v caps
2 3.3uf, 50v caps
4 10uf, 25v caps

F1208 Filter Block
4 ZTX795A transistors
2 10uf, 25v caps
 
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I have started replacing caps and things, and noticed I made a mistake in ordering one value of caps.
The caps for F-1208, F-1209, and F-1228 with the value of 10uf, 25v are actually that value, but bi-polar/non-polar electrolytics (Nichicon UEP1E100MDD). I have searched and seem to see contradicting advise on replacing with non-polar. It would appear as though it depends on the location.
Can anyone advise on what to do with those three boards?
 
mikeinit said:
I have started replacing caps and things, and noticed I made a mistake in ordering one value of caps.
The caps for F-1208, F-1209, and F-1228 with the value of 10uf, 25v are actually that value, but bi-polar/non-polar electrolytics (Nichicon UEP1E100MDD). I have searched and seem to see contradicting advise on replacing with non-polar. It would appear as though it depends on the location.
Can anyone advise on what to do with those three boards?
Click to expand...

On my AU999 they are polarized caps as indicated by the screen printing on the circuit board, I recommend to replace with whatever value and polarity came out.
 
kevzep said:
On my AU999 they are polarized caps as indicated by the screen printing on the circuit board, I recommend to replace with whatever value and polarity came out.
Click to expand...

Thanks, I thought that would make the most sense also. Just double checking, just in case.
 
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