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Carver M1.5 t power supply repair

Posted: Mon Mar 25, 2013 9:45 am
by Retriever
Moved from home audio thread
Carver M1.5T Power Supply Repair
Ok so I'm new to this site!
I decided it was time to refurbish my M400t after 26 years of reliable operation. Before I start on this amp I bought a project amp, a M1.5T that is dead. Actually its not dead it has a shorted Triac and fires up with a varactor properly. To the point...

After scrutinizing the schematics
the steering bridge diodes I read as FDH 400 ( 1 shorted) (1n4148) m400t
Seems like 1n4005 would be suitable.

The Triac is Q6025 t0-3 pack.
The Diac is HT-40

My question is the Opto coupler a MTC-275?
I could not find a part number in the 1.5 T schematics, however the M400t schematic (New Series Power Supply) lists the Opto as a MTC-275.
The part number is indistinguishable on the device...
this crosses to a ps2601 or 4n35 both I have..

Is this correct?

FYI I'm an engineer who worked as a tech wile going to school years ago, and currently Employed as a Sr. Software Controls Engineer. I have repaired high quality amps before (SAE) and have all the necessary equipment. Cudos to this sight for posting the Service Manuals, Just got the M240 manual for my car amp that still works, but needs some new capacitors in the supply.

Re: Carver M1.5 t power supply repair

Posted: Mon Mar 25, 2013 10:23 am
by TNRabbit
Welcome, Retriever!

MOST of the techies are located on

We have a couple here, but most of us aren't at the level you're talking right now.

Regardless, welcome to the forum!

Re: Carver M1.5 t power supply repair

Posted: Wed Mar 27, 2013 8:19 pm
by Retriever
FYI anybody who's interested 4n35 optio is good, unit is up commutation is good according to scope. Letting it run for tonight on the bench for testing. While that was testing re-capped my M400t woa did the amp wake up! Had to back down the bass. Sounds smooth as ever! Got all the parts from Newark Electronics in 3 days! Now to recap the 1.5t tomorrow. Hope the 1.5t sounds as good as the M400t at moderate levels!

Re: Carver M1.5 t power supply repair

Posted: Thu Mar 28, 2013 8:25 pm
by Retriever
Well everything is great on the 1.5 t passed all the power tests, however I'm not to fond of testing the short circuit protection at power! I kinda feel like no one out there?
The original culprit was the +-12 volt supply, oscillations present after warm up, replaced the low voltage electrolytics and supply cleaned up ( after replacing all the high voltage electrolytics including the dual caps).
Parts so far
Q6025 triac
40 volt diac
4n35 optocoupler
4 1n4004 diodes
2 47 uf 20 volt caps
2 2200 uf 50 volt caps
2 2200 uf 100 volt caps
2 4700 uf 200 volt caps
Overkill on the voltage ratings but hey it's my amp!
Some refitting for the slightly larger electrolytics.
Beating the amp up on the test bench Priceless!

Re: Carver M1.5 t power supply repair

Posted: Sat Mar 30, 2013 2:43 pm
by Retriever
Ok all you audiophiles out there now that the 1.5t is operating I've been comparing the sound.
To me it seems the M400t has more prescience in the low end than the 1.5t. As an engineer, I was wondering if the higher capacitance values in the M400t 4700uf in low voltage with an additional 2200 uf stacked at the mid voltage has some factor where the 1.5t low voltage 2200uf and the mid voltage is 2200 uf non stacked. Does anybody have any thoughts?

I have some poly caps on order for the 1.5's Signal path maybe that will help nullify the difference?
Could it be after 26 years I'm partial to my restored M400?