Carver TFM 45 DC offset

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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?
 
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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
 
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.
 
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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
 
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.
 
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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
 
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.
 
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Hi mura,
At D30 I would expect to see -31VDC, D31 should read -67 VDC in normal operation. Measure these at the cathodes.

An interesting clue emerges now that I think about it. Have you lost the ground from the input jacks to the common on the amp boards? That would be pin 10 on the connector, where R6, R7 and C4, Q1, R5 and R11 connect on the amp board. Measure with your ohmmeter to the pad on the supply PCB. There were some problems with cracked solder joints with the PCB connections to the power supply board in the past on some amps. Use some solder flux when you resolder them, also clean the pads up before you reassemble and check for disconnected pads. Check the pins on the amp boards as well.

-Chris
 
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Hi mura,
Great to hear! Good going.

Bad caps are possible, but I think it was resoldering the amp board connections to the power supply PCB that fixed this. That has been one of the answers to this problem in the past.

I am sure the caps could use changing at this point in time anyway.

-Chris.
 
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Hi Iagent,
Sorry, I didn't have that much contact in the 'States. Look for a service guy who does audio only. He will probably be in his 40's or 50's and he will have a good reputation for neat work. He will have worked on mostly better products. His per hour rates might be higher than average, but the job will be the least expensive through him. So there is his profile.

Great TV techs do not service audio well, but they will be convinced that they do. Car amp guys and pro amp guys will probably not do a proper service job, although there are the odd ones who are good. Then we ask "why are they were they are"?

I'd have to see that one on my bench to troubleshoot it. There could be a number of things causing that. From filter capacitors, to noisy trimmer controls or solder joints. Most likely a combination of those things.

-Chris
 
Service Manual For TFM45 Power Amplifier

Dear Mr Mura,

I also have a Carver TFM 45 Power Amplifier But when it was converted from 110v to 230v by my technician he forgot how to reconnect the transformer wires. Therefore I would be highly oblidge if you can send me the copy of the service manual by mail or just send me the page where they have showed the transformer connections. I hope you will help me.

thanking you,

Homiyar Merchant
Gandhi Mansion, FlatNo 1
16 Wadia Street,
Tardeo, Mumbai 400 001.
09821214981
mhomiyar@yahoo.co.in
 
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