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Old 19th July 2005, 10:32 AM   #1
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Question Bad Carver M1.5 Power Transformer??

I am having problems with my Carver M1.5 amp. It acts like the transformer my be bad but I have never had a transformer act like this. With the transformer completely out of the amp,the secondary windings are not hooked to anything and using a Variac on the input widings, I can feed this transformer with 45 volts all day and it will just get warm but push it to 75 volts on the primary and it draws 9 amps on the primary side. At 45 volts in I only get about 75 volts - + on the highest rail. My 1.5T runs 125 volts - + . If this transformer had a shorted winding it would get hot and smoke at any voltage,it does not. It acts like the core saturates at about 50 volts and any more than 50 and you are pushing it hard. Any Ideas?? Many thanks, Al

What should the rail voltage be set at on the M1.5 and 1.5t Carver amps?
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Old 19th July 2005, 07:49 PM   #2
Allexx is offline Allexx  Ukraine
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I had the same problem repairing Carver about three years ago. It was blowing mains fuse. As I remember that amplifier has interesting voltage regulator based on triac circuit controlled by feedback signal from the secondary rails via optocoupler. I disconnected all the loads and triac circuit but it was still blowing fuses. I came to conclusion that transformer had short circuited windings. All attempts to find substitute transformer failed. Now I do not know where that amplifier is. It seems to me that for some reasons related to that voltage regulator circuit and triac the core is heavily magnetized. Try to do something applying AC voltage to secondary winding slowly raising it up or maybe discharge 10000 or higher value capacitor charged to 50V via secondary winding with all the windings open. If it will not help change the polarity of the winding while you discharge that cap. It seems to me the only way to demagnetize the core. One of the ways to check short circuits inside transformer is to apply low frequency signal to any of the windings and check the form of the signal at any winding using the scope
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Old 19th July 2005, 08:32 PM   #3
anatech is offline anatech  Canada
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Al's Electronic,
The transformer is a MAG COIL. It does not run on a sine wave. Your observations are normal. The supply is preregulated with a triac. Do not plug it in if the triac is shorted!

You have three bipolar supply rails. The top was set around 118V (or 125V, I can't remember). What is the voltage rating on the big caps? You need to set lower.

Use caution as this amp will put out every watt that is advertised. Common failures are supply caps going open, some resistors changing value and an input coupling cap intermittent connection. This does not include "struck by technician". We were the Canadian factory service shop for Carver.

-Chris
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Old 2nd August 2008, 05:34 PM   #4
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Default Carver 1.5 Fan PCB burn, protected

Hello:

I need some help from the carver amps gurus, I got in Ebay this amp with the Fan PCB burnt, so I fixed what looks an easy fix, but the protection did not fix, the around 50 voltage is lower than it should, so I wondering if the PCB shorted caused a damaged on the transformer
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Old 7th January 2009, 02:27 AM   #5
anatech is offline anatech  Canada
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Hi jle_tarzan,
The "transformer" is probably okay.

This is not the type of amplifier that non-professionals should attempt to service. Your top supply rails are + / - 125 VDC and do not discharge on their own very well.

Given the age of this amplifier, it will need a number of things looked at. If there is a good technician who really does understand Carver products, take your amp in for him to service. It doesn't take much to really hurt or kill yourself working on these amplifiers. It's also very easy to cause a great deal of expensive damage.

This is really not a good amp to service without knowing exactly how it works.

-Chris
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Old 6th April 2011, 09:41 AM   #6
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Default Carver PM1.5 heavy current draw

Quote:
Originally Posted by anatech View Post
Hi jle_tarzan,
The "transformer" is probably okay.

This is not the type of amplifier that non-professionals should attempt to service. Your top supply rails are + / - 125 VDC and do not discharge on their own very well.

Given the age of this amplifier, it will need a number of things looked at. If there is a good technician who really does understand Carver products, take your amp in for him to service. It doesn't take much to really hurt or kill yourself working on these amplifiers. It's also very easy to cause a great deal of expensive damage.

This is really not a good amp to service without knowing exactly how it works.

-Chris
I've got the same problems after repair of a Carver PM1.5.
I'm an expierienced engineer, able to repair al kinds of pro power amps, including the digital ones
While the amps are old, they're still in use.
At this example I replaced the dual capacitors, because there was no capacity at all anymore.
After replacing the fuse, the amp seemed to be without defects.
But when I applied an testtone of 1000Hz, the fuse blowed after a few seconds. Only one channel driven.
I live in the Netherlands and the amp is factory connected for 230 volts, so the fuse has to be 6 1/4 Amps slow blow.
I tried to measure the primary current draw and used a FLUKE 177 in series with the amp. Currentdraw with one channel driven was over 10 amps, meter reading overload.
Using a currentclampmeter, I measured over 15 amps. That reading could be faulty because this was not a true RMS meter.
I checked the triac circuit and also the firing of the triac. That seems all correct. Conducting time varies with current consumption.
I borrowed another amp, which i tought it was a good one, but there was fitted a 15 amp fuse. So this amp could have some (or the same) problem.
A third amplifier used still the original 6.25A fuse.
When i applied a 1000Hz sinewave and a dummyload of 4 ohms. Current draw was also over 10 amps with one channel driven.
Is there anyway a method of checking the transformer (magcoil), so i can exclude that part.


Greetings from Holland
Speakertech
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Old 6th April 2011, 11:44 AM   #7
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the mag coils cannot be run at more than 60vac(120v US model) when connected directly to the AC line/variac. the service manual has a statement about jumpering past the triac and bringing it up slowly to 60vac and you should observe full rail voltages at that point.

and I second. these are very complex amps that require a full understanding of there design!
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Old 6th April 2011, 02:38 PM   #8
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Yes, I do understand the principles of the amplifier.
As you stated that all secondary voltages should be nominal for a mains input of 60 volts at an amp that is constructed for a 110 volt line, I understand that if the amp is wired for 230 volts (original wiring from factory for europe), The input voltage must be around 120 volts from variac.
I just checked the value again and the RMS voltage (with FLUKE 177) reads at idle 91volts AC input for 126 volts DC on the highest rail. Current draw is about 0,3 amps RMS. This is with normal triac drive.

Tonight i'm going to connect my variac, to check the voltages with a sinewave input.
In Europe we use a mains frequency of 50Hz. I've never heard of problems, related to the mains frequency. Those amps are sold in Europe since 1984.

As you know, i'm not the only one facing this problem and readig many forums, i learned that the mag coil doesn't fail in most cases. However, i never read the solution or explanation of the problem.

Speakertech
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Old 6th April 2011, 03:12 PM   #9
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Here are some values measured with an AC variac. European mains. 230 volt 50 Hz.
No signal, no load (There is no offset at the speakerterminals !)


Input voltage at current draw of 300mA , 110 volts AC, 126 volt rail reads 69 volts DC
Input voltage 155 Vac, currentdraw 3 amps, highest rail 100 V dc
Input voltage 195 Vac, currentdraw 8,5amps, highest rail, 126 volts.
When you want to know more values or other tests, plse let me know

Speakertech
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Old 7th April 2011, 10:18 AM   #10
djk is offline djk
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A Carver with a triac supply must never power up the transformer with a sine wave supply and a variac. Use a triac light dimmer with a narrow conduction angle.
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Last edited by djk; 7th April 2011 at 10:21 AM.
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