G6000 protection problem.

[anderslober]

Hi forum......I have not been on the forum for a while. No worries.

I have a g6000 on the bench....totally recapped....new main tr`s...deoxited an`all.

I just cant get the unit out of protection on DBT. DBT light is dim......no major shorts. No smoking. Outputs are fine.

By chance I had another g6000 on hand so I could test the driver board. It worked fine in the other unit. So driver board is ok.
Power supply voltages are what they should be.....

Just no relay click.......any ideas? Thanks....

 

[LBPete]

Have you measured the DC offset at a point before the protection relay? It may just need adjusting. Can you post a picture of the the board with the relay and the power supply board? I may be able to direct you to a good test point.

- Pete

 

[anderslober]

Hey Pete.....I will try to measure voltage before the relay. I have 4 meters hooked up. Two at the speaker outputs and two meters for bias.

I have adjusted the dcoffset and bias as stated in the SM.....but of course since the relay does not click....dcoffset cant be measured at the speaker outputs.

Nothing is smoking or burnin`.....when I adjust the bias, I can feel the heatsink changing temp.

One thing......on the driver board...there is a 4-pin connector at the top of the board(signal and gnd L/R)..does this need to be connected when doing measurements?

 

[anderslober]

Using the `scat......measure at r05/r06? Seems like a god place to measure before relay......

 

[kevzep]

Anders!! Wow!! Long time!!

What bulb have you got it on? Could be the DBT keeping it in protection, but before we assume anything do check the DC offset at the Zobel network before the relays.

 

[skippy124]

Hi Anders

You can also use either of the bias test points (measure voltage on either of the bias test points to ground) for each channel to check the offset pre relay. Final check then done at the speaker terminals.

Cheers

John

 

[anderslober]

Aaayyyh Kev!..........no worries...!

I have checked the dcoffset voltage at r05/r06...before the relay....I managed to dial in almost 0mV. At the same time, I checked bias...dialed in 4.0mV both sides. All on DBT. I am using a fairly large watt bulb...150w.......I will change it.

What are you workin` on? Hehe...

 

[anderslober]

Changed bulb to 100w.....still no relay click. Voltages seem good..........

 

[bberkom]

Changed bulb to 100w.....still no relay click. Voltages seem good..........

You need a larger bulb I think, not smaller. The amp potentially isn't seeing enough current to get out of protection.

 

[anderslober]

Ok....will try my 200w bulb. Not long ago, I did one of these amps and 150w bulb was easily enough then.....

Could the relay tr be bad? Sometimes these Sansui circuits are notoriously touchy!

 

[kevzep]

After I've done the housework I'll have a look at the schematic and see what we can figure out.
Could be a number of things at play here...

Anders, I seem to be a magnet for Sansui QRX receivers at the moment!!

 

[kevzep]

I would actually as a matter of course, replace the SCR, I have seen a few of these go bad, they just go flaky and false trip the protection, last one I had doing that was in the AU-X1 I was working on.
Just replace it, I use 2N5064, they seem to work in all the Sansui's Ive encountered...

Once you've done that, then see where your at....

 

[anderslober]

Yes..the SCR.....suspected that too......I will replace. Gettin` close......

Those big QRX`s are awesome......absolute wonders! to work on.

 

[LBPete]

The larger the wattage of the light bulb, the lower the voltage drop in the amplifier. A 60 watt bulb will cause a much larger voltage drop than a 100w bulb. No need to use a bulb larger than 100w. If you want to go there, just plug it in without the DBT.

- Pete

 

[Hyperion]

The larger the wattage of the light bulb, the lower the voltage drop in the amplifier. A 60 watt bulb will cause a much larger voltage drop than a 100w bulb. No need to use a bulb larger than 100w. If you want to go there, just plug it in without the DBT.

- Pete

+1 On this, for this size of amplifier 100W is sufficient, and you won't achieve anything by going higher - providing you have no bright bulb after the first few seconds of power-on.

 

[anderslober]

Changed the SCR......still cant get it out of protection. Any other ideas? Nothing smoking or burning....all ps voltages are ok. Bulb is dim.
Relay tr possibly?

 

[anderslober]

Measuring at the emitters on tr01 and tr02...I am unable to get the bias below 45mv on both channels. Adjusting vr6/5

Give some good measuring points to me.........so close now....

 

[Hyperion]

One thing......on the driver board...there is a 4-pin connector at the top of the board(signal and gnd L/R)..does this need to be connected when doing measurements?

That connector you mentioned, I would suggest that you DO need to have it connected when setting DC offset.

Not having the input connector plugged in can affect the input differential pair, with consequent knock-on effects for setting DC offset.

 

[larryderouin]

One more thing. When on the DBT, and adjusting bias and offset, set them back to minimum settings BEFORE plugging in to the wall, or the settings you have now on the DBT will be too much when on wall voltage. On the PIONEER forum they call it "tickling the Dragon". And you DON'T want to wake him up enough to breathe fire and smoke!

 

[anderslober]

I actually plugged it in the wall.........no smoking or burning......

Could a relay actually become defective?? I did desolder the relay and check it/clean it......it seemed a-okay.

I desoldered ALL the tr`s in the protection. ALL tested good.

The driver board is a-okay,as it worked in another g6000 I had on hand.