Just shooting the breeze Carvin 400FET

[DrGonz78]

So I have this Carvin SX400 or better known as Fet400 for repairs. Anyway the guy who had worked on this amp really hacked it up good!! Just Nasty!

Well I have a quick question about the mosfets on this amp... They need to be insulated from the heat sink right? Well I would guess so and apparently these mix-matched pairs are all shot! That will be the first line of sight to fixing this amp. I mean look at how sloppily this thing was worked on.

Notice there are no insulators on the Mosfets, plus a horrible amounts of thermal grease.


Also here are two version of REV-C 30-04028 power boards for the 400Fet that I can find online. One of them was redrawn and is way easier to read but they listed their drawing as REV-G 80-04028. They look identical so there was something lost in translation.
fet400PSrevC30-04028.pdf
carvin_fet400_sch.pdf

Well as you might have noticed in the pic of the power board, mine says REV-B 30-09008. Just looking at the other schematics and then my board there is something way off here... Does anyone have other schematics for this amp or do you know if Carvin will send out schematics? Any thoughts on this post are very much appreciated. I will try to fix this beast but the guy modded a bunch of crap too. Working without a schematic will be interesting because who knows what was designed or modded. Thanks for reading.

[Enzo]

Don't ask us if Carvin hands out drawings, ask CARVIN, then come back and tell us.


Board revisions are not always easy to see and may not affect the schematic. Schematically, it could be something as simple as adding a tiny cap from heat sink screwhole to circuit ground. Or it could be changing some caps from 600v types to 1000v types. But sometimes the difference could be they reworked the board itself to have wider traces in one spot or moved a screw hole in another. SOmetimes they change vendors and respace some solder pads for some part.


What is this amp worth? What are they selling for? Before you rebuild the power amp, have you fired it up without the power amp to see if the preamp and stuff all works or will also need work? It is one thing to fix an amp that died, it is another to undo changes and damage and THEN repair it. Point I am getting to is consider whether the repair makes sense. Will the guy accept a $250 repair bill on an amp worth $150?

[Leo_Gnardo]

Does anyone have other schematics for this amp or do you know if Carvin will send out schematics? Any thoughts on this post are very much appreciated.

Every time I call Carvin for help, no dice. "Carvin does not supply schematics or parts. If you are having trouble with your Carvin product, send it back and Carvin techs will restore it to 'as built' ie: just like new condition."

Thanks to the internet some schematics are available. Sorry I have none to add.

A local guitarist sent back his combo amp (@$100 shipping), and it was returned EIGHTEEN MONTHS LATER (more $$ shipping). Still had the problem it was sent back for. So much for Carvin "service." I avoid working on their amps as much as possible and I recommend that customers avoid buying them.

DrGonz, if you're going to tackle that prize you're much more adventurous than me. I wish you the best of luck. (Also thanks for your comments & analyses on the More Board Problems thread.)

In their favor, I've seen some very good Carvin basses & guitars which seem an excellent bargain for the price.

Carvin amps, I wouldn't shoot the breeze, I'd shoot the amp. Phooey!

[Enzo]

Interesting. I don't know their current policy, hence my suggestion to ask them. But every Carvin schematic I have in my files came direct from Carvin.

[Gtr_tech]

If you see cut/jumpered traces don't assume it is a mod. Its real common to see "on the fly revisions" on carvin stuff.

[drewl]

here's a link to Carvin schems.
The one you have should be close enough for repairing it.

CarvinService.com - Schematic Finder

[DrGonz78]

Hey thanks for all the reply's!! Yeah the amp belongs to me... LOL! Basically, I buy amps that will make me go insane!

So, Enzo the parts and time are mine all mine. I will learn from my endeavors or I lose my profits. Basically whatever I sell this amp for is profit after parts to fix it. So, I spend $20 parts and shipping... Well then I sell it for $60-100. Basically, I can make $40-80 depending on my luck if I can fix it or more. Worst comes to worst I can use the shell of the head to build my first born amp!! YAY! I bet it can be fixed if it is not too badly hacked up... Well, the headphone jack looks like it's been modified as a switch between channels or rather EFFECTS. Yeah this thing will be a headache but more of a learning tool. The real profit will be if I can pull it off. I love the challenge and at the same time I just want to learn more about amps.

Leo thank you! I appreciate you telling how it is out here in Carvin Hell. The other Carvin amp I messed with was from the 70's and let's just say that thing is still waiting for me to go another round with some more testing. Basically, I like the fact that Carvin has many old schematics online but let's just try calling them to see about board revisions. I bet no dice like you said... Thanks for the forewarning. Also, yes their guitars and basses look really nice in the brochure I have in the mail every 3 months. I will try to sweet talk them on the phone and report back...

Gtr_Tech yup I understand that completely. I see all sorts of *possibly Carvin* mods on this amp but the headphones output jack is connected to the XLR type channel/effects switch in the back of the amp. I got this amp along with a Fender Performer 1000 and a nice 12" speaker. I paid only $100... The Fender Performer had what(G-One Nailed it) I believe to be plumbers type solder on the 9-joints of the input jack. It was the nastiest cold solder joint ever. Anyway, the guy I got this amp from said it was worked on by a buddy of his. His buddy told him >>> "This amp is a lost cause". Now yes most of the mods might have been how Carvin put this amp out originally. Either way I just got to hack it up better than that guy's buddy did.

Drewl I stared at this schematic long and hard trying to envision how this version is laid out. There is FET 900 out there too and this amp is just an earlier version. Trust me I have all the versions of the schematics on that site. The more readable version was redrawn and put up by someone on the ElectroTanya website.

So, would everyone agree that there needs to be insulators on the mosfet output transistors? Hey this way we can hack it up together, Right?

[Leo_Gnardo]

Also, yes their guitars and basses look really nice in the brochure I have in the mail every 3 months. I will try to sweet talk them on the phone and report back...

What I tell my customers is Carvin's best product is their CATALOG. Super groovy photos with star filters, gear arrayed on stages with smoke drifting thru (hint of what's to come...). Looks like Candy Land don't it?

Somehow Enzo gets respect from Carvin, as he should. They always put me on hold for 20 minutes or so, then put on some sweet sounding receptionist (never a tech, maybe 'no habla ingles') who coyly gives me the same old line. Reading between the lines, it seems they're worried someone will "reverse engineer" their precious amps and start to turn them out in competition. HAH! Fat chance I say to that!

I'd plan on putting insulators between those power mosfets & heat sink. FWIW I did own a FET900 for about 10 years. Blew out a channel but I managed to fix it without a schemo. What was surprising - most of the box was filled with air. Transformer here, power surprise & amp boards over there. Lotta space in between.

[g1]

So, would everyone agree that there needs to be insulators on the mosfet output transistors? Hey this way we can hack it up together, Right?

Not me ...yet. Seem to recall some old Fet amps that didn't use insulators (Ashley???). Could be totally wrong of course, but I'd like to see the exact schematic and how the heatsink is connected to the chassis before condemning anything. Also, testing Fet's can be difficult. Many I thought were shorted were not.

Edit: Ok, looking at the schem. and photo, I'm convinced there should be some insulators there!

[Jazz P Bass]

The back plane of the high side FETs is at +Vdc.
Correct?
So if the heatsink is isolated from ground & -Vdc, then no milar.
The same goes for the low side, but opposite polarity.
The two transistors, one on either end, may need them.
The one is marked Q36.
The other is covered by that big cap.

[km6xz]

I have a different take on Carvin. When I contacted them for information and the availability of parts, they were 1 of the only two companies in the MI industry that were helpful and assured me that I could get any parts I needed. The bench tech I talked with, by email, sent a schematic I needed, plus some personal notes from his experience with a model we discussed and part numbers for some OEM parts needed, and offer to send them to me personally.
The only other company taking customer service seriously in other countries is Visual Sound. Peavey
(actually they said they would help but Peavey US has no clue what their divisions in Europe is doing and won't do, and apparently does not care if new units have any recourse for warranty or non-warranty repairs), Fender, Roland, Marshall, Neve, Loud, and 50 more I have contacted refused to even discuss making parts available. So Carvin gets a gold star in my book.

[Jazz P Bass]

The few times I had to contact Carvin, they where very helpfull & informative.

[Enzo]

Gonz, what do you mean by redrawn? In post #1 you link two drawings, but both are Carvin work. The one was old style, the multicolored one is the newer style of more recent Carvin prints.

[DrGonz78]

Well I will call Carvin on Monday as I was just so busy today. Hopefully they will be of assistance and can provide a schematic.

Actually I must apologize to all on this thread as I must clarify what power amp module we are seeing. As I had stated on my first post that this amp is an SX400 or also known as Fet400. I wish I had read up a bit more on that statement. They are totally two different amps. However, the power board is very much similar as I have looked at pics of the Fet400. Here are some pics from someone online that has worked on the Fet400. Looking really hard I swear I see mica insulators between the mosfets and the heat sink. The heat sink connects to ground through the chassis so this would make sense. Thanks Jazz on your explanation on that one too and G-One as well.

http://0.static.wix.com/media/1a24df...51.wix_mp_1024

It shows the PCB 30-09008 REV A. I guess reading the different schematics I was hung up on what I was missing on this power board module. Also, have to say that the redrawing of the schematic was only a thought that the first one was not very legible. Enzo I see more clearly how they are different now and a later revision. Sometimes I get lost in this stuff and come out looking like a fool. Still some of my best lessons have been learned by being a fool too.

Hey Leo if you think your FET400 had a lot open space then you should this monster chassis!! lol

There are 2 IRFP250 and 4 IRFP250B mosfets here... Also, the 2 transistor drivers on each side are TIP107's. There is a lone transistor driver on the on the other side of the board that reads TIP31C. I believe the TIP 107's were once TIP31C's. The drivers are not shorted but every one of the six IRFP250 transistors are shorted. I searched for TF15N20 and MTP8N20 and got a perspective of the mosfets used in the past. I guess these IRFP250 are way better and should be good replacements for this amp. Any better ideas?

Sorry for my misunderstandings going on here with this amp and thanks to all who have contributed. Hopefully this clears up my posting a bit so others will follow along better too, thanks.

[Leo_Gnardo]

Well I will call Carvin on Monday as I was just so busy today. Hopefully they will be of assistance and can provide a schematic

If they give you a hard time just tell 'em you were sent by Enzo, Stan & Jazz P Bass. They will roll out the red carpet, give you a kiss on each cheek from their cute receptionists, a hearty handshake from Prince Carvin himself & then place a glass of fine California champagne in your hand. "Now what can we do for you Dr. Gonz?" Who knows, maybe they took a lesson from Peavey in terms of cooperating with us repair people. Let us know how ya make out.

Hey Leo if you think your FET400 had a lot open space then you should this monster chassis!! lol

900 it was but no matter, a "box of air" compared to say BGW or Peavey CS800 jam packed with huge xfmr, beercan caps, circuit boards & heatsinks. Nonetheless, the FET900 performed admirably. I usually used it to run monitor wedges.