AU D11 II in protection mode

[leesonic]

That was exactly why I changed out all the trim pots. They've been sitting in the same position for the past 20 years, and now we come along and start adjusting them.

You might also look for dry joints on the board. I had one on mine that caused one of the adjustments to jump all over the place. The solder joints between the main board and the upright daughter boards can cause problems as well.

Lee.

 

[djef]

OK, I'm changing those trimmer pots. Where did you find 470ohm 3296p? Neither mousern nor digikey carries them. Did you use 500ohm? That's the closest value they carry. I imagine that would work, just don't turn it all the way to 500.

 

[djef]

Well, I replaced the trimmer pots on f-4296,f-4266 and f-4267. But I still can't get it to work right. I'm following the instructions in the manual. First I adjust the EQ amp, then the Tone control amp. Then on to the driver boards. This is where my problem is. I can adjust the hot/cold balance on both boards, but when I get to the center DC adjustment, I can only get it down to around 6 volts. The trimmer is turned all the way, but it is not at all close to 0volts. However, if I turn the bias current up then the center DC will come down and the amp comes out of protection.
Does anyone have an idea what the problem could be? Possibly some other components on the driver boards could be way off spec, but the DC is about equally off for both left and right sides and it seems improbable that the same part of each board is equally amiss.

 

[Hyperion]

Try not to worry too much about the centre DC voltage adjustment (otherwise known as the HOT-GND adjustment). Although you should be able to adjust it using kVR2 to zero volts - it won't stay there for any length of time and will drift quite alarmingly - this is a known problem.

I am puzzled by the following that you experience with your amp...

Well, I replaced the trimmer pots on f-4296,f-4266 and f-4267. But I still can't get it to work right. I'm following the instructions in the manual. First I adjust the EQ amp, then the Tone control amp. Then on to the driver boards. This is where my problem is. I can adjust the hot/cold balance on both boards, but when I get to the center DC adjustment, I can only get it down to around 6 volts. The trimmer is turned all the way, but it is not at all close to 0volts. However, if I turn the bias current up then the center DC will come down and the amp comes out of protection.
Does anyone have an idea what the problem could be? Possibly some other components on the driver boards could be way off spec, but the DC is about equally off for both left and right sides and it seems improbable that the same part of each board is equally amiss.

Are your output transistors still getting hot with the bias set (as far as you know) correctly?

If so, please explain exactly how you are measuring/setting the bias, where you are measuring, and what meter readings you see.

 

[JOMARK911]

Let me chime in for a while.
I adjusted a d11mk2, a few hours ago.
It is a great pain to bring hot - cold balance , and then to bring zero . But once you have it you have it.
L channel sat right there at 0,00mv , with the first try.
Second like r channel gave me a hard time , really hard, it sat on 3 mv .
I let it there. The next measurments went fine ..
I would change those trims for sure, if it where mine.

 

[JOMARK911]

I had a lesser hard time adjusting the old G 22000 , but hey !!! .
I also did a au-x1 , in the past hour .It went like a charm. The smoothest bias and dc offset allignment ever.
She got it from a bazaar , along with a 4060 tt , and wanted to know what was wrong with the amp . Not to mention the worn out needle .
Some people are so lucky....

 

[rasenthiran]

Bazaar?? If only I have one...

 

[JOMARK911]

Yeah life is unfair.

 

[djef]

I took step by step photos to show exactly what I’m doing and what my problem is.

First, I do the EQ adjustment.

Then the tone.

Then on to the power amp adjustment. First, the Hot/Cold balance. These two will go down to 0V +-5mv.

Left

Right.

Then on to the center DC voltage. This is where it gives me trouble. With the trim pot turned all the way down, it only goes down to about 5 volts.

But if I turn the bias current way off base like so-

The center DC will come down to around 2 volts (still too high) and the protection relay clicks off and puts the amp into normal operating mode. But, as you see, the bias is far off and the transistor gets hot.

Center DC with high voltage, hot transistors-

 

[richka]

I don't have manual,but i think AU-DII it's simliar to AU-G99x.If that's a case:
Check dc voltage between trim pots.It should be 0.07v.
On my G99x was 0.2V and there was more than 5v to the transistors.And i can't lowered it with trim pot.
I found integrated FET(NEC UPA68H) was bad on F4296 board.Replaced it and problem was gone

 

[djef]

I think that a bad UPA68H might definitely be the problem. I'm looking at the schematic and I see that it directly affects vr1 and vr2. The AUD11 and AUG99x are indeed very similar.
Where did you order yours from? Mouser doesn't carry them.

 

[djef]

The only place I can find them is on ebay, from china. With shipping they're about 7$ each.
I read that it is also possible to use 2 transistors as a substitute. I'll look into this and maybe try it.

 

[Hyperion]

This might help... I think the equivalent 2SK129A is also difficult to get.

2SK129A – but this is a can type with 2 groups of 3 legs not SIL like the above.

UPA68H

NPN Monolithic Transistor Pair - JFET,VGS(off) 2.5V
NEC Electronics
Transistors,JFETs,Junction FETs
Number of Devices=2
V(BR)CEO (V)=50
I(C) Abs.(A) Collector Current=30m
P(D) Max.(W) Power Dissipation=250m
h(FE) Min. Static Current Gain=5.0
@I(C) (A) (Test Condition)=1.0m
@V(CE) (V) (Test Condition)=10
Semiconductor Material=Silicon
Package=SIP

EDIT: Update
Also this http://www.littlediode.com/product.php?productid=365524

Drill down and UPA68H = 2SK129A = 2SK389

If you chose to use individual transistors note that these are JFET's which need to be matched.

These:
http://www.bdent.com/2sk170v-f-toshiba-low-noise-transistor.html

 

[richka]

http://www.audiolabga.com/mal_cart/mal_cart.php?find=UPA68H&search_request_button=Search
I ordered from this site.Received them in 2 days.

 

[Oiltanking66]

Hello!!

I have an AUD-11-ii in protection mode, finally what was the failure in your amp? It was the JFETS (upa68h)?

I tried to find the failure follow the advices in this fórum with no good results

I will appreciate your support!!

 

[quadklipsh]

Yeah please conclude the exercise for other readers. We appreciate