Mark Levinson No23 repair help

[Handel]

I cannot understand why I have so high voltages from the regulator. +-105V at the VCCregs and +-17V at the V buffers. I do not have SAT resistors present. If I increase the resistor R100 value, should the VCC reg go down? Decreasing the value, VCC reg should go up?

 

[Hans Polak]

Vcc should be ca. +-83Volt and Vbuffer +-12 Volt..
A SAT resistor is nothing but Resistor Select At Test, meant to do the fine tuning.
But I'm surprised the voltages are that high.
So what are the +-V Pre Regs voltages and what are the voltages on the zeners D5 and D6 ?

Hans

 

[Handel]

OMG, +-152V at pre regs. How is that even possible?

 

[Hans Polak]

Wrong setting for primary transformer voltage.

Hans

 

[Handel]

312v from the wall. Time to call electrician

 

[Hans Polak]

Are you measuring rms or peak voltage.
220V rms is 310V peak.

Hans

 

[Handel]

According to the manual of my multimeter it can show only mean value.

 

[Hans Polak]

You multimeter might be wrong.

Hans

 

[Handel]

Quite unbelievably, now 230v from the wall socket.
+-119v at pre regs, +-78v at the regs and +-13.7 at the buffers. Something like it should be?

 

[Hans Polak]

78Volt is a bit on the low side, but harmless and 13.7V is a bit higher as expected but also completely harmless.
What caused those erratic voltage readings ?

Hans

 

[Handel]

That is still unclear. Electrician is visiting tomorrow to check the electricity of the house.
Is there way to tune the 78V and 13.7V independently?

 

[Hans Polak]

Yes of course, by means of the SAT resistor you can increase the 78 Volt, but leave the 13.7 Volt as it is.

Hans

 

[Handel]

Ok. There was nothing wrong with the electricity in the house. All the cables were tight. It is mystery. One thing needs to be checked. We have installed solar panels a few months ago. The inverter might be causing this...

 

[willcycle]

Attached to the an amplifier heat sink is two each MJE15030 and MJE15031, however, if you look at the schematic it only shows one '30 as Q38 and one '31 as Q50. Where are the other two transistors?

 

[Handel]

One set is in the pre driver, the ones you mentioned and second set is at the voltage regulator.

 

[willcycle]

Is it on a different page? I just don't see the other ones. Do you have a reference number?

 

[Handel]

Yes different page, #186 on this topic

 

[willcycle]

Thank you. I now have four pages of schematics. Is that everything?

 

[Handel]

Should be: ac-2, vb-4, ol-2 and regulator.

 

[willcycle]

I am having a problem with the soft start circuit not activating relay k300 to short out the three 10 ohm power resistors on startup. My suspicion is a shorted Q300.

My understanding of this circuit is when first powered by 20V DC transistor Q300 is fully on preventing current flow thru coil K300. As capacitor C316 charges, current flow thru Q300 decreases until it turns off after C316 has 20V across it (less emitter to base diode drop). At this point all current flows thru the coil, activating the relay. I am waiting for a replacement TIP125 to arrive before testing.