Carver TFM-55X Mag field PS regulator problem

[nites]

I cannot turn this amp on for more than a few seconds as the main DC voltages rise to more than 110volts and the amp hums/buzzes very loudly.I have checked all semiconductors and passives on the regulator PCB with a multimeter (in-circuit). I also checked the 35A TRIAC (and the TO-92 triac) ,and replaced the op-amp. I looked at the drive signal to the TO-92 triac gate on a scope (for the few seconds I can power it) and there was no signal at all noticeable on the scope.

Is the any way to power this long enough to trouble shoot the regulator ckt without doing severe damage ?

[llwhtt]

See if you can get in touch with Anatek (Chris) on this forum, he's the resident Carver guru. He's been on lately so maybe he'll see your post.

Craig

[Tajzmaj]

Hi.
I have some 30 carver amps for live touring system. I also service many of them and have all service manuals for models which I have.....
There was only a few different psu basic circuits so I will glad if I can help you....
There is possible to connect amp on variac and gradually increase voltage. At some 30 volts ac the amp should work and you will be maybe able to locate problem. If you already checked triac than can be tricky to repair it......I can share some experience.
At PM 1.5 I have found once bad trimmer pot which is used to adjust psu voltage.
Because you mentioned small to92 triac I think that this is the same psu which was developed for PT1800/2400 amps.....At PT2400 once I discovered this scenario...
Because one of the big smoothing caps die amp try to charge it but it never reached wanted voltage. So all other voltages were way too high but amp try to charge that cap. The result was several destroyed caps and burnt resistors. My advice. If you can't get some variac connect amp to mains via 100W bulb and measure voltages on the smoothing caps. If you find lower voltage on some of smoothing caps that one is bad. Because there you have triple psu you must check all 3 voltages. For such amp is something like+-35,+-70, +-120,+-12 volts normal. That last +-12v is used to power small signal circuits..... If you want I can check values in service manual, of course if we can determine which is the closest to your amp....
There is also good idea to chech all bridge rectifiers and diodes.....
Ah and now I remember that at that PT2400 was also a burnt 1N4148 diode.....I can also try to remember which.....because there is a lot of them....
So try confirm that tfm psu is similar to that one from PT2400 amps and we will try to figure out something.
Best regards

[Tajzmaj]

I checked. It is little different but similar.....
http://thecarversite.com/manuals/fil...e%20manual.pdf

[nites]

Hello Tajzmaj
Thanks for the help.I haven't yet had time to try the variac supply,do you know how much current it should draw when running on the variac at ~ 30vac ? I have checked the bridge rectifiers for all three supplies with no problems. The 96v supply is not being restricted as it immediatly goes to > +/- 110v in 2-3 seconds but I haven't yet checked the other two - thanks for that suggestion.Is the 96v supply the one used to monitor the transformer (mag coil's) output to regulate the triacs "on time" thru the op-amp & optocoupler? Also shouldn't I be seeing some evidence of the triac's control signal at the opamp's or optocoupler's output - even though it's only powered on for a couple seconds?.
I'll let you know if I get it powered up on the variac.
Thanks again,
Best Regards

[nites]

Hello Tajzmaj
I tried to power it up with a variac and it does not respond at all,draws no additional current when the power switch is turned on. I am applying ~ 30vac at power cord.

[Tajzmaj]

Hi
When you connect such amp to variac you must short triac first. Otherwise the amp will fire up but at voltage high enough and you won't be able to measure anything.......Short A1 and A2 of the triac and than slowly open variac. And measure voltage on big smoothing caps. I'm Not sure but at some 50vac will the transformer goes to saturation and will draw high current. You will hear buzing....and you won't get full voltage on psu at that moment because this transformer can't be in full conductive cycle at voltages high enough to get 96V at psu......

[Tajzmaj]

Ah I almost forget.
I was unable to open manual of tfm amp but Pm and PT amps use all voltages....to monitor voltage. At some amps m,ybe not all but at least most of them.....of course positive and negative as well.....uf complicated but still can fail....
Regards

[nites]

I shorted the triac and it powered on as you said, I turned the variac up until the 96vdc supply reached +/- 55v. The other two supplies have equal +/- voltages. At this variac setting it's only drawing 140mA. So far don't see any problems yet.

Thanks again
Best Regards

[Tajzmaj]

You can also connect amp on variac but put some bulb (40-60W) in series, and try to reach 96V......or at least some higher voltage. But it looks like that it is still something wrong with regulation of primary...There can be defective opto coupler or some of transistors at steering circuit...don't be afraid of this amp....There is nothing very strange and special inside Which oc is used? If I'm correct CYN17-2