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Sansui 6060 shorting ? when I turn up the volume.

Sansui 6060 shorting ? when I turn up the volume.

  • Sansui 6060

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  • shorting

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    1
H

Harreld

New Member
Hello I have a question,

My Sansui 6060 seems to short circuit One channel output transistors has already blown, I replaced it with MJ21193G & MJ21194G.
The Sansui 6060 has had a complete recap, with parts from peace.love.music from ebay and everything assembled via the manual.
It works well, only if I turn the volume up high then my Light Bulb Current Limiter turns on and there is a crackle coming from the speaker, I quickly turn the volume knob down again, the lamp goes out.
I also tried without the Light Bulb Current Limiter, but that cost me a bunch of output transistors and fuses.
Bias is set at 10-15 mv.

What could be causing this? I don't dare unplug my 6060 from the Light Bulb Current Limiter right now, and turn up the volume.
 
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Couple possibilities -- bad transistors in the differential pairs, bad driver transistors, bad power supply. You will need to check voltages for both channels at idle (zero volume, no input) and see what's going on there.

My guess, and it's only a guess, is that turning up the volume rails that channel, probably due to excessive offset.
 
HPMguy said:
Couple possibilities -- bad transistors in the differential pairs, bad driver transistors, bad power supply. You will need to check voltages for both channels at idle (zero volume, no input) and see what's going on there.

My guess, and it's only a guess, is that turning up the volume rails that channel, probably due to excessive offset.
Click to expand...

Hello thanks for the response.

The offset in idle mode is +-10mv for both channels, adjusted with the speakers connected, speaker knob on A, volume all the way down, and selector knob on aux.
All transistors and capacitors and diodes etc on the driver board have been replaced.
 
You should not be using the unit into a load with the DBT connected.

If DBT dims with no load (no speakers connected), volume at zero, selector to AUX, and relay clicks in, you can then measure offset safely at the speaker terminals. Do this by putting speaker selector to OFF, insert meter probes into A terminals, then turning speaker selector ON. Turn OFF before removing probes. Report back.

Also, check bias with unit on DBT (no load, volume at zero, selector to AUX). It should be around 12mV on both channels when on DBT. Not sure what you mean by "offset in idle mode". Are you referring to bias voltage or DC offset voltage?
 
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remove dbt .check/set dc offsets and idle bias . then try playing music .
it may be your speakers or wires doing it .
 
spark1 said:
You should not using the unit into a load with the DBT connected.

If DBT dims with no load (no speakers connected), volume at zero, selector to AUX, and relay clicks in, you can then measure offset safely at the speaker terminals. Do this by putting speaker selector to OFF, insert meter probes into A terminals, then turning speaker selector ON. Turn OFF before removing probes. Report back.

Also, check bias with unit on DBT (no load, volume at zero, selector to AUX). It should be around 12mV on both channels when on DBT. Not sure what you mean by "offset in idle mode". Are you referring to bias voltage or DC offset voltage?
Click to expand...
 
Idle offset I mean the device is on and volume down, speakers on A, selector on AUX, BIAS Voltage on channel L and R +-10mv
 
I assume that the protection relay is closing?

What is BIAS voltage while on the DBT?

What is OFFSET voltage while on the DBT?

Disconnect the darned speakers for these measurements!!

If bias voltage on DBT is 10-12mV, good. If not, adjust. If offset is less that 25-50mV, good.

Now take it off the DBT. Connect speakers (be sure to use speakers known to be in good working order, as a shorted speaker can trigger the protection relay and/or damage your amp). Power on. Assure relay closes. Try playing music. Report back.
 
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There is no DC offset adjustment on the 6060. The driver board input transistors need to be gain matched.
 
Bias may be much lower on the DBT, I always check, then turn way down before applying mains power, then set on mains. I've seen it jump quite a bit.
 
Turning the volume up would not cause the unit to go into protect mode if the diff pair transistors are not matched. There could be DC on the volume control caused by a leaky coupling cap in the preamp.
1. Disconnect your speakers.
2. connect a meter to one pair of speaker terminals.
3. with no signal, increase the volume control while monitoring the DC voltage on the speaker connectors. If it stays at 0V and the protection relay doesn't trip, the problem is not DC offset.
4. If it doesn't trip the protection relay with no speakers attached and no signal, check your speakers, you may have a frozen voice coil on one woofer.
 
Can I make a guess that your speakers are rated at 4 ohm or less? Too little impedance can make an amp act like you are describing.
 
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