Starting my Au-999 Recap
- Thread starter tobyj17
- Start date
kevzep
Its all about the Music
Okay so take a step back.
We are powered up with the driver boards out.....
The bulb is dim, yes?
So, on the right channel with the black probe to ground measure
1> Terminal 22 on the F-1277
2> Terminal 18 on the F-1277
3> Collector of the front output transistor
4> Collector of the rear output transistor
5> Collector of the 2SC driver transistor
5> Collector of the 2SA driver transistor
List the voltages you are getting.....
tobyj17
Comfortably Numb
Okay powered up.. fuses in both sides..driver boards out.. here's what I get:
Dim bulb..
1> Terminal 22 on the F-1277 -46.8v
2> Terminal 18 on the F-1277 18v
3> Collector of the front output transistor 18v R/S 0v L/S
4> Collector of the rear output transistor 46v same for both
5> Collector of the 2SC driver transistor 46v same for both
5> Collector of the 2SA driver transistor -46 for both
Dim bulb..
1> Terminal 22 on the F-1277 -46.8v
2> Terminal 18 on the F-1277 18v
3> Collector of the front output transistor 18v R/S 0v L/S
4> Collector of the rear output transistor 46v same for both
5> Collector of the 2SC driver transistor 46v same for both
5> Collector of the 2SA driver transistor -46 for both
kevzep
Its all about the Music
The cap with the orange wires is the negative DC supply....So you will see the orange wires coming from the bridge rec (-) and to the negative on the Capacitor, then the positive of the cap goes to ground....
Then the -45VDC supply goes to the F-1277 board......as well as terminal 5 on the opposite channel driver board and terminal 17 on the F-1231 board on the other side of the amp....
Then the -45VDC supply goes to the F-1277 board......as well as terminal 5 on the opposite channel driver board and terminal 17 on the F-1231 board on the other side of the amp....
kevzep
Its all about the Music
Okay cool Toby, this is telling us something.
There should be 0VDC on terminal 18 F-1277.....Let me have a look at the diagram, I will report in a few minutes.....
tobyj17
Comfortably Numb
I've got the orange wire going from the - on the rectifier to the fuse, neg. side of the cap, and to terminal 28 on the f-1277 board.. the other wire goes to a fuse on the other side.. through there it turns to white, then on to pin 9 of the driver board socket.. and to pin 28 of the f-1231 board
kevzep
Its all about the Music
Okay, lets take the driver transistors out, and measure terminal 18 again.....
kevzep
Its all about the Music
That is correct.........
tobyj17
Comfortably Numb
Alright.. all four drivers out..terminal 18 is at 0 volts
kevzep
Its all about the Music
Okay, do you know which driver transistor came from the position where we were getting the 18VDC reading on terminal 18?
If you do, then put the other one in instead, and power it up and re-measure terminal 18....
Must be getting late over in Wisconsin......:scratch2:
tobyj17
Comfortably Numb
Yeh..it's about 1:30 am.. but in order to get assistance from someone half a world away.. ya gotta do what ya gotta do. No biggie.. I've got nothing to do tomorrow. I like the look of that 9090..it's pretty!
Anyways.. I put the transistors from the channel that was reading 0v..and I still get 18v on terminal 18..
I also swapped them.. and I still get the 18 volts
Last edited:
kevzep
Its all about the Music
Cool, yeah I like the way the owner of the 9090 whom I sold my AU-9500 to gets me to work on a really minor problem and just leaves it with me....He reckons he will pick it up in about 6 months.......:thmbsp:
They sound okay, probably the best from the era, I think they sound better than the AU-9500......but they dont quite have the full weight and detail the G22K has.....but I wouldnt say no, not by any stretch, they are a good amp none the less....:yes:
Okay, back to the issue..........
What if you loosen the screws which hold the driver transistor in, jusy loosen them all the way off, then carefully do it up until the screws just "nip" the transistor....
Do the same thing with the output transistors too......
Now to be clear, this is the Right hand side, with the F-1277 board...right?
What Im thinking is there is a partial short circuit somewhere around this driver transistor or the output, logic tells me its something like this........
If you set you DMM to Ω and measure between terminal 18 and the Emitter of the 2SC driver, which is the red wire, you should have a very high reading of about 10meg and floating around, then if you reverse the probes, it should be reading OL......
If you put the driver board in, with the power off, you should see the R851 220Ω resistor on your meter which is on the driver board......
kevzep
Its all about the Music
Okay, thats good Toby........I'm convinced its not the transistor sockets now....but this is good, all the while we are eliminating things and getting closer....:thmbsp:
I think I might have found something.....Im starting to attempt to simulate this fault on my amp....
Stand by.....Im doing some fault simulation.......
kevzep
Its all about the Music
Okay, put the driver board in the left channel with the power off.....
Measure from the emitter(Yellow wire) of the 2SCXXX driver, to terminal 17 on the F-1231, you should get the 220Ω reading again....
Then go from terminal 17 to the emitter of the 2SAXXXX driver (yellow again) you should get 15Ω.........
The problem would appear to be in the left side, when I took my driver board out and powered it up, I was getting voltage on terminal 18 as well.....
Now thats good, but why was there no erroneous voltage the same on the other channel?
So now we move and investigate the left channel.......
Measure from the emitter(Yellow wire) of the 2SCXXX driver, to terminal 17 on the F-1231, you should get the 220Ω reading again....
Then go from terminal 17 to the emitter of the 2SAXXXX driver (yellow again) you should get 15Ω.........
The problem would appear to be in the left side, when I took my driver board out and powered it up, I was getting voltage on terminal 18 as well.....
Now thats good, but why was there no erroneous voltage the same on the other channel?
So now we move and investigate the left channel.......
tobyj17
Comfortably Numb
Emitter to terminal 17..yes I get 220ohms..
Terminal 17 to the emitter of the 2saxxx..i get 16.5 ohms.
Not real sure what the hell I did.. I'm probably going to kick myself for a month after we find it!!! Oh well.. at least I've got the big G still working and playing away :thmbsp:
Terminal 17 to the emitter of the 2saxxx..i get 16.5 ohms.
Not real sure what the hell I did.. I'm probably going to kick myself for a month after we find it!!! Oh well.. at least I've got the big G still working and playing away :thmbsp:
kevzep
Its all about the Music
Good, thats what it should be, what we will do now is work with the right channel, we know from the readings that this is the same as mine with regards to the chassis and the F-1277 board..........
So, we are going to disable the LEFT hand channel, remove components so we can eliminate it screwing up the supply for the good channel......
Okay, take all the output and driver transistors, and the driver board, OUT of the left channel.
We are now going to put the driver board in the right hand channel, fit the outputs and power it up on the Dim bulb....
Turn that bias trimmer all the way ANTI-CLOCKWISE..............
Clip onto the emitter resistor nearest the front of the amp....and lets see what we get.......