Carver TFM 45 DC offset

[mura]

I have a Carver TFM 45 with DC offset in both channels,

I also have the service manual with which i have checked all parameters and i could only find this wrong:

At the D30 and 31 i get a reading of -48V instead of -15V
and -33V.

The supply voltage is 60VDC with the Triac Removed.

Any ideas?

[anatech]

Hi mura,

Any ideas?

Back away from the amplifier very slowly. Do not apply power to it. Take it to the nearest service depot that was authorized warranty for Carver. Tell them exactly what you did.

I can tell you that you didn't take the time to read Section 4 "Circuit Description". By doing what you have done, you almost injured yourself and may have caused extreme damage to the amplifier. I do commend you that you did take the time to get the service manual, but without an understanding how it works you can not repair it. Techniques for servicing this amplifier are somewhat different to most amplifiers.

The supply voltage is 60VDC with the Triac Removed.

The supply voltages are now very much higher than what you think. There are three bipolar supplies for the amplifier sections.

You survived. That is cause for a celebration.

-Chris

[mura]

Hello Chris,

Thanks for your input.

Back away from the amplifier very slowly. Do not apply power to it. Take it to the nearest service depot that was authorized warranty for Carver. Tell them exactly what you did.

1.I think you misunderstood me.

2.No Carver Service in India.

3.I am aware of the different supply Voltages of this amp.

I am used to working with a lot of high power and high voltage systems and i follow Safety measures.

The exact problem with this unit is that after following the service manual instructions of removing the Triac and using a dimmer to input less than 60V, i get a HUGE DC offset in both channels.

By HUGE i mean if the Main DC rail is 25V offset is around 20V negative or positive.

In one channel it is positive offset and in another it is negative offset.

[anatech]

Hi mura,
From what I saw, you seem to have way too high a voltage.

So what do your high rails measure right now?

-Chris

[anatech]

Hi mura,
I was just thinking. I have never seen the suggestion in a manual that a dimmer be used in place of the triac. That is not the procedure we used in Carver service.

Anyway, we were the factory service at the distributor in Canada. I'll try to help you out if you can get the right measurements.

-Chris

[mura]

Hello Chris,

I was just thinking. I have never seen the suggestion in a manual that a dimmer be used in place of the triac. That is not the procedure we used in Carver service.

I am not using the dimmer in place of the triac but i am using the dimmer in the mains input to limit the AC voltage to below 60V as stated in the service manual.

[anatech]

Hi mura,
Interesting. I've not seen that, but then we were trained much earlier on the product.

What do your rails measure first of all? Right at the rectifiers. Also check the op amp supplies for bipolar 12V or there abouts.

-Chris

[mura]

Hello Chris,

Thank you very much for you reply, i have to get back to you on this tommrrow since i am away from my house.

[anatech]

Hi mura,
That's fine. Do not allow the high voltage rails to exceed 125 VDC, I set them for 118 VDC in operation.

-Chris

[mura]

Hi Chris,

What do your rails measure first of all? Right at the rectifiers. Also check the op amp supplies for bipolar 12V or there abouts.

All the rail voltages are in spec.

I have removed both channels from the Power supply board and checked all the pins(which join the amp channels to the PS board) for the respective voltages according to the service manual.

The op amps get right voltage.

Again this is what i find wrong:

At the point D30 and 31 i get a reading of -48V instead of -15V for D30 and -33V for D31.


For the above mentioned check of the D30 and D31 i used a dimmer to keep the input voltage below 60V with the Triac Removed as mentioned in the manual.


The main problem is the High DC in the output,one channel is positive the other negetive.