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Re: Ampeg SVT 3 Pro output has DC

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11/8/2005 12:22 AM

Re: Ampeg SVT 3 Pro output has DC

I found it on a disc, send me your email addy with SVT3Pro Schematic as the subject.

Try calling Yamaha for schematics. They have these wonderful service manuals for everything. Utterly complete little books with schemos, patrs lists layouts, mechanical blowups, disassembly pocedures, diagnostics, specs, you name it. $15 and up. SOme are over $40. First rate, but not cheap.

Try calling Roland, DOD, Digitech. They all charge. it is more common than you think.

PV has a good plan, they email them out for free, or charge $2.50 for paper copies. That doesn't always cove the postage let alone the labor and materials.

I don't think SLM charges a lot. it is not cheap mailing that stuff out. Go price 10 pages of 11x17 at Kinkos, an envelope to fit, postage, and your time and mileage to go to the post office.

My load mention was because a solid state amp needs no load. So you don't need to burn up your load, plus if it is just DC on the output, it won't draw excess current until loaded. SO you can chase down the problem while it is powered and do it in a liesurely fashion.

Just include the cost of drawings in your labor. The guy doesn't need a sad story. Besides, it is never a good idea to dis the brand the guy has purchased.

I think it is good you stand behind your own products. I stand behind my work too. Crate/Ampeg stands behind their prodcuts by issuign warranties and signing agreements with shops like mine to provide that service. Most brands will not cover abuse or drinks dumped into things, but orkville, bless their hearts, offersd a ten year warranty for any failure for any reason, beer included.

If you are not used to working on solid state, this amp might not have been my first choice as a project, I'll admit. Give me a box full of 15 year old PV SS heads anytime, I can crank them out a mile a minute.

11/8/2005 1:14 AM

Bless you, bless you.

Yeah, I know the synth/processor folks charge for service manuals, but what you get is a service manual, and that is accepted in that market. The devices are unique and complex. I would argue that there is a different tradition/practice with basic amplification. The last vintage Ampeg I had in had the schematic pasted inside the cabinet (it proved to be the wrong revision, but the thought was nice :-)

:-)

.

For client repairs, all I want is an electronic copy of the schematic diagram. Mailing a hard copy service manual is going to add 3 business days to the down time of their unit.

Peavey, Laney, Carvin, Fender, Marshall, Mesa, they all make their schematics available instantly for free.

I don't trash talk the product, but people do ask me which companies are helpful and which are less helpful, and I tell them. I believe in that helpfulness as a selling point. Companies who make it easier for my clients to get their gear back on the road should be rewarded.

I work on solid state stuff quite a bit (I'm one of the few indie techs in my area who will), lots of Marshall Valvestates show up, had a Fender Cyber-Twin in here last week. SWR's, etc. This one is just the proverbial tough doggie.

11/8/2005 5:10 AM
Erik Miller	Before I go off to bed: the gates and sources of the high-side MOSFETS are at -70, the drains of these are at +70. All 3 pins of the low-side MOSFETS are at -70. I'm poking around Q5 next....

11/8/2005 9:53 PM
Enzo	Let us know...

11/9/2005 2:26 AM
Erik Miller	Well, replacing Q5 didn't fix it, nor did replacing 4 of the 1K (spec'd as 470 on the schematic) gate resistors that had drifted up about 50% in value. You're right, the power section alone is a pretty danged simple circuit, and it seems like I've probed and/or replaced almost everything. I'll go back and try some more of the specific suggestions you and R.G. had.

11/9/2005 7:13 PM

Don't rule out the 3440 or 5415. I had a GK 400B that ENZO also helped me with and the 3440 tested ok but was bad. Just beware because if it is the problem the dang thing will start pulling current like a big dog and take out anything around what's not connected in the circuit. But hey at least it's doing it's job. If it makes you feel better I lost a speaker a while back too but never again

11/15/2005 3:51 AM

Knowing when to quit?

I've replaced Q7-Q14; R25, 32, 34, 35, 37, 40, 41, 42, and 43; Q2, 4, 5, and 6.

The only active device on the output board that hasn't been replaced is Q3, because I could not find one. And except for the big MOSFETS, everything diode tested okay after I pulled it, including Q3.

I've tested every diode on the board, and they all test good.

It still puts a solid -55V DC across the output.

I don't like giving up on any repair, especially now that I have a schematic, but I've run out of things to try, unless anyone has any further ideas.

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