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 :xeye:

What should the rail voltage be set at on the M1.5 and 1.5t Carver amps?
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
Joined 2004
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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.

Carver 1.5 Fan PCB burn, protected


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:smash:
Joined 2004
Paid Member
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.

Carver PM1.5 heavy current draw

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.

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
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!
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.

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

Here is a page from the Carver TF-45 service manual. page 19 that states:

"Troubleshooting can be simplified by shorting across the triac with a jumper wire. This bypasses the triac control and allows 100% of the line voltage to be applied to the transformer. there-fore, never increase the line voltage beyond about 60VAC when the triac is bypassed."


  • Carver TFM-45 Service Manual Page 19.pdf
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No the manual in that section is talking about fault conditions. "IF" it draws more than 1 amp there is a problem. the pages previous it mentions bringing an unknown amp up on a variac at various voltages(without the triac bypassed) at 60vac line it should be drawing less than .25amp, at 85vac less than .5 amp and then at full line less than 1 amp.

They also state what the PSU voltages should be and any LED's that should be lit etc etc. the manual is VERY well detailed. it is available on the carver site dot com and 99% of it applies, at least the operational theory applies to most of the carver amps so its an interesting read.

The carvers were a lot less scary once i realized its just a flippin light dimmer firing the transformer. In fact i even use a triac based light dimmer to test fire one. and what was really interesting is that this is the same basic principal behind the Souncraftsmen PCR power supply regulator circuit. and I believe that Ralph Yeoman from SC was the first to do this. Carver just copied him. or worked with him or whatever. In fact Soundcraftsmen was the first to use rail switching Class-H circuits!!!
Okay, all facts ar known here. Testing faulty amplifiers, is always done with a variac and a lightbulb, to protect the amp, as far as it is not totally defective.
Applying those items is satisfactory for measuring shorted output tansistors, faulty rectifiers and so on. Those repairmethods are all wellknown here. It is not the first amp on the testtable.
Carvers 60 volt limitation has to do with the fact that the powersupply is fully unregulated, when the triac is shorted. Applying more than 60 volts at idle, could result in too high secundary voltages. For repairpurposes, you initially don't need more.
As I stated, the amp draws in idle condition, with triac regulator operating, about 300...350mA. Mainsvoltage in Europe is 230 volts 50Hz. Should I connect the amp for 120 volt, currentdraw could be about 600mA, but I never tested that value. Its below 1 amp. By the way, it's difficult to measure drawn current from mains, because the current is far from sinoidal. At first I tested with a clamp ammeter. later on I connected a Fluke 177 true RMS meter in series with the mainslead. In the manual is nothing described how to measure the current. So differences in measuring can occur.
With the amp running idle, all DC settings and voltages are OK.
Primairy voltage at the transformers input is about 93 volts RMS with the amp running idle. (Attention, we have 230 volts mains)
It would be great to know what is the input voltage after the triac with one or two channels fully driven. Does anybody know that?

Although have a complete manual here, i noticed that the faultfinding paragraph is on other pages as mine.
So i like to know where I can download the example that's mentioned in this thread, simply to get more information about the amp.

The PM 1.5 service manual does not have the detailed troubleshooting information that the TFM-45 has. I would cross-reference the two manuals. use the TFM-45 manual for basic troubleshooting how too and the PM 1.5 manual for exact specs, schematics etc. briefly looking at the two side by side they are nearly identical.

I cant remember the models. but there was a home and pro model that were the same. it may be these models?
I read that TFM-45 servicedoc for additional info.I looked at the oscillograms for the triac,
In the PM1.5 manual the triac is conducting for about 40% of time at idle. There is no oscillogram for full load.
In The TFM-45 manual, the triac is also conducting for about 40%, at idle and about 66% for full load. So there is a regulation of about 25 percent. Thats a great difference with mine amp. At full load, one channel driven, it reaches a conducting time of about 90%, resulting in a primary RMS AC voltage of about 200 volts. DC level at the highest rail decreases to about 110 volts DC. Thats a great difference and i've no explanation for that'.
On the secondary side, all capacitors are in good condition and all diodes are good, so there is a full wave rectifying.
The amplifier stages use little current when unloaded, so they are not suspected.

I have some 30 Carver amps. I use them for touring, have serviced most of them and have almost all service manuals. So if I'm correct TFM uses psu from PT1800/2400 but I,m not sure. So my advice. Remove all wires ( red yellow and orange if I remember correct ) short triac and measure voltages to the ground, where center tap is still connected( black wire I think) Use variac or 40-60w bulb to reduce input voltage and measure output ac voltages on the transformer. You should get all voltages symmetrical. Do you check bridge rectifier as well? it is mounted near big filter caps.
Then of course is possible that triac fires asymmetric. Good choice is to replace it if you have one on hand. Some caps on regulator board can also be defective. And there is psu board which have a lot of caps some of them exposed to the heat of resistors.....once i found defective trim pot which regulate psu voltage. It is also possible that is something wrong on the amp boars. There are a lot of things which can go wrong there. If you need any manual I can scan it for you.
I have 10 PM 1.5-1.5A-PM1200 amps which I mostly bought from ebay and some 80% of them were broken. I get them cheap.....But non of them has burnt magnetic coil transformer. They all works. With such heavy wire it is almost impossible to burn it. And believe me I drive and abuse those amps hard. Because of high psu voltage they have high headroom so they don't tend to feedback. I use them to drive wedges.
Mmmmm loud and undistorted. Lots of punch.
Hello Tajzmaj,
all items you mentioned above are already tested.
New capacitors.
diodebridges tested for full wave rectifying,
Correct firing of triac.
Symmetrical conducting of triac
All those items are tested.
My entrance to this thread was a measurement on a separate transformer, like one of the first topics in this thread, a clean transformer drawing havy currents and not reaching nominal secondary voltages.
But is was stated that sinewave power could not be applied to this transformer. Indeed, when i connected it to the pcb's and applied mains, all things seemed to be solved. When idle, the amp runs properly. Without a load, the amp can be driven to clip and takeover of the voltagerails is correct. Ripple on the 36 volts rail is minimal and ofcourse practically zero on the higher rails, because there is no load at this moment.
When I connected a dummyload the amp gives full power with a sinewave signal, 600 watts per channel.
Then the fuse blows.. A sinewave is not always a real situation, so i tested the amp with a normal musicprogramme from cd. After a few minutes the fuse blowed again.
After that, I measured currentdraw from mains and that reached 15 amps, one channel driven. A problem i have not solved yet.
Is there any good method, to test the mag coil, to know that the magcoil is't sure not the problem?
I have another magcoil and it reacts the same.
I borrowed an amplifier which i tought is was a good one, but it was fused wit 15 amps (amp wired for 230 volts), also drawing that heavy current.
I'm not the first person with the same phenomena.
What else could it be.
I'm an experienced technician, in repairing all kinds of pro amplifiers, not just tv-set engineer.
Once in your life you get an unsolvable problem and here it is.......
Btw i owe all needed docs

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