Sansui AU-D11II Kicking Into Protect Mode

[Zekeman]

I have posted quite a bit about my D11II. Today while cranking it up a bit (to 11 o'clock-ish) it kicked into protect mode while playing a tune that hits with quite a bit of bass.

It has been totally recapped except for the main large filter caps. Just two weeks ago I set all the offsets and bias'.

What would cause this?

Any advice will be appreciated.

Thank You.

 

[Zekeman]

No it does not stay in protect. Once I turn down the volume pot it comes out of protect.

 

[Zekeman]

I have new relays on the way so I pulled the back of the amp off today to remove the existing ones and to inspect the power supply board. There are a number of diodes on the board. With them still mounted to the board I took readings and got the normal 0.45 to 0.55 but when I reversed the multimeter leads I am NOT getting "OL" but positive readings!! I tested three of them and the same thing. The amp, mind you works fine until I really crank her up. Why would I get readings on the diode with the leads reversed?

 

[Zekeman]

While I have the rear-end of this thing apart, are there any other components on the PS board I should consider replacing in addition to the relays?

Thanks.

 

[Zekeman]

I pulled one of the diodes and it tested OK...so the diode phenomenon above must have been due to in-circuit issues.

 

[twc5964]

It's very possible the main power supply caps have reached the end of their lifespan and needs to be replaced.If i'm not mistaken it's from the early to mid 80's.Some equipment can last 40 years no problem with the same caps...some dont.Yours might be one that does not.I'd first try new main power supply caps unless you find the problem elsewhere first.Have you checked all solder joints ?

 

[ericson38]

Going into protection means the speaker feed current being sensed by the protection circuit was too high, at least the unit thought so. This is not a sign of weak main power supply filter caps. On the contrary.

See if you can make this occur on one channel, using the balance knob. This can zero it down to the side that has a problem.

 

[Zekeman]

there is a mod to the protection boards that need doing, changing some resistors in a sansui document

Thanks...I did that mod when I originally restored it in the Fall of 2007.

I also checked the impedance of my speakers (JBL L96's) and both clocked in at 6.3 ohms. So no problems with them.

I'll try to isolate once I get the new relays in. I dread having to put it all back together and then taking it apart again.

This amp does sound beautiful but it is turning out to be a bit of a PITA.

I'll report back after further testing.

Thanks all.

 

[Jon_Logan]

.....did you replace all of the electrolytics? If the amp has over current protection, sensed by a voltage drop across an emmiter resistor.... .....there usually is an electrolytic cap that integrates the current, firing the protection circuit. An open or changed value emmiter resistor will cause this too.

See if it goes into protection unloaded as well.

Another thing.... check the tweeter. A DC resistance reading of the speaker will miss a shorted tweeter condition due to the HP filter.

 

[Zekeman]

.....did you replace all of the electrolytics? If the amp has over current protection, sensed by a voltage drop across an emmiter resistor.... .....there usually is an electrolytic cap that integrates the current, firing the protection circuit. An open or changed value emmiter resistor will cause this too.

See if it goes into protection unloaded as well.

Another thing.... check the tweeter. A DC resistance reading of the speaker will miss a shorted tweeter condition due to the HP filter.

Thanks. The entire protection board was recapped in the Fall of 2007 with Panasonic FC's. It does not go into protection until it gets to 11-12 o'clock.

 

[Zekeman]

See if you can make this occur on one channel, using the balance knob. This can zero it down to the side that has a problem.

Well you were right...tuned out to be the right channel. The "center DC" adjustment....supposed to be 0 mV and was running at 266 mV. So I went back and forth through the adjustments and it now works properly. I let it warm up quite awhile prior to adjusting.

I also installed three new relays...and finished recapping four difficult-to-get-at caps on the tone control board near the bass and treble pots.

Thanks to all for their guidance!!