Bose 1800 series VI Pro amplifier not turning on & Peavey PVi 3000 no output

Hello all,

This Bose didn't turn on one day when I come to use it. It was working fine the time before so no sudden shut down. I've finally got it out of the cupboard to have a look at it.

It still don't power up so checked the plug fuse, that has continuaty and I have continuaty from internal fuse to switch and from the switch to the board it goes to so presume they are fine.

From what I can see there's no burnt components and no bulging caps.

I wanted to know if you guys know of any prone problems with these amps and before taking it apart further to check buried boards if I should check anything else out. I understand those 22,000uF caps won't mess about in killing me so Im carefully respecting that.

Any ideas will be greatly appreciated as usual.

Also got a Peavey PVi 3000 of my brothers that turns on but no output, it was repaired at one time beforehand and has a suspicious dent on top from the inside going out, like a caps blown upwards ha. Lent him my Crown amp for now.

Thanks

Edited after update: I sold the Bose for spares or repair, so no fix here!
 

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I'm currently working on the Peavey (Really I should of done separate posts) and I get music through it but very distorted, only very low volume it's 90% OK, moving the pot up anyway sounds terrible. I've blasted the pots and sockets with Deoxit, slightly better sound. I took the pots out, outside contacts & solder joints are clean but when moving the pot it seems like the wiper is grinding very hard, could it be the problem? Im considering taking the pot apart before I order some better ALPS pots or something.

It also seems like the guy who serviced it previously did a great job of cleaning but I feel he may of used a poor contact cleaner as all the connectors, speaker binding posts and input Jack's I'm using are effecting the sound, the Jack's sockets can turn the sound off completely, this could be why my brother got no output at all, twisting the Jack's gets a signal.

I've blasted the sockets with Servisol Super 10 but still not sorted the jack problem, I'll take the board out and clean them better and check the solder joints.

I'll take some pictures too, not sure if this glue is the conductive type too.
 
Further troubleshooting on the Peavey. I removed the input board with the Jack's & speaker connection and cleaned all the pots and switches with Servisol, reflowed all the Jack's and speaker connectors solder joints only because they were thin, one of XLR joints had a hole in yet I wasn't using them inputs earlier. Seem to go no better, worse if anything, really struggling on the bass mainly.

I noticed a quiet hum coming from the transformer even when the socket had power but no switch on, I'm thinking that is suspect and needs looking at, although I've tighten the bolt but it didn't move.

I did poke about abit while it was playing music through one channel and notice the component on the heatsink in the middle, never seen one before, when wriggling the wires it had quite a bit of change, never went better yet was going worse. The connections don't look the best.

Any ideas will be greatly appreciated
 

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turk 182

Member
2012-10-26 3:03 pm
if you've never seen a thermal cutoff before i guess you don't know that it's there to remove the supply line to the output stage in case of a thermal fault condition, and if it does have bad connections then wiggling them will have an audible consequence your changing the supply voltage!


please tell me your doing this "testing" under current limited conditions a la Dim bulb tester!?
 
Thanks guys.

I don't have the dim bulb tester yet. I just wanted to check if there is anything obvious and got a bit carried away. Definitely shouldn't have. I'll stop till I get the DBT.

The Peavey had terrible solder joints done by the last guy in here. Seems the regulator was only on two pins, broken badly, I did try resolder it but it made no difference. I'll have to repair the joint completely when I get the DBT.

On the Bose I did get continuaty on the output transistors. I am guessing it's something to to do with the triacs

Thanks again for your help and guidance. I'll be back when I get my DBT.
 

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turk 182

Member
2012-10-26 3:03 pm
stress fractures from thermal cycling are inevitable the ones that occur from transportation (and like much pro gear it's moved long before it's adequately cooled ( as in "i got the money for the gig let get out of here, there's cool beers waiting at home")are caused by mechanical shock.


try checking things over with a magnifying glass, that could be quite revealing!
 
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I didn't realise that. Thanks for that info as it's good to know and makes a lot of sense.

I've order the DBT with extra 100w bulbs for spares. I used to have one with a scope (which I never got round to using) but didn't take them with me when I left the ex, she deserved a form of wave anyhow, testing a different kind of broken board.

The regulator heated up well so could this be the problem? Broken solder joint.

I thought it was the volume pots at first but it's not a static or popping sound, just distortion particularly in low end and sound goes in and out. I'm thinking that's because there's not enough power getting to the power amp boards.

Also one of the big 10k filter caps is slightly bulged than the other. I'm thinking that's why there's a little buzzing on the transformer.

When it's fixed I was planning on testing all the caps and replacing the ones testing bad. Now thinking of recapping the psu when I get it out with Panasonic caps.

Thanks for the tips, I'll magnify the joints when I get it back out.
 
You need to measure the DC voltage on rail caps as you turn up the volume with a load on speaker terminals. I use 10 ohm 450 W (series 2 ea. 5 ohm 225 W) resistors I got from a surplus house (apexelectronics.com apexsurplus.com) but a cheap junkyard 4 ohm speaker will also work. If voltage sags as you turn up the volume, the problem is in the power supply. Use 2 clip leads, never use 2 hands measuring voltage with power on. No jewelry either.
Rail caps can limit output wattage themselves due to high internal resistance, but usually don't cause distortion, just a polite sound with no volume changes. An analog VOM on AC volts 20 or 50 can measure music coming out, P=(V^2)/Z where P is rated wattage of the amp and Z is rated impedance of the speaker/load resistor. Less wattage on speaker than the rating is a bad sign of rail caps.
distorted sound at higher volume sounds like bad solder joint or bad crimp on the flag terminals. Crimp terminals can be re-squeezed. use Klein or Ideal tool for decent results.
I found a 100 W bulb to have too much resistance for a 1300 W Peavey amp. The op amps wouldn't operate. Series the AC input I used a resistor bank from a 1500 W room heater (120 vac) with a bad tip-over switch. It conveniently had flag terminals on it. Kept the dodgy (not shorted) output transistors from blowing the tops when they shorted.
 
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Great advice indianajo, well appreciated.

I use a junk full range driver I use for testing things first. I will get some big resistors as well as other test equipment as I seem to be repairing /restoring alot of amps now.

I can't find the schematics or service manual for the Peavey PVI 3000. I wanted to check the levels when I'm done with it.

I don't have any spare resistor banks spare I don't think and would take more time to get some delivered. Will a lower wattage bulb be better? I can get them easily down the road

Great advice on the filter caps. I've only witnessed some were faulty when I had humming on an amp and changing them got rid of the hum.
 
I don't have any spare resistor banks spare I don't think and would take more time to get some delivered. Will a lower wattage bulb be better? I can get them easily down the road
Lower wattage bulb is worse for high wattage amplifiers. You might be able to get a 5-10 ohm high wattage resistor with an in cup tea boiler, or an electric tea kettle. But you'll have to keep water in them to keep the element from burning out. Our dollar stores & resale shops do not have tea boilers of any kind. Tea comes in gallon plastic jugs now, pre-brewed. [email protected]#$. Dead room heaters can be found here on the side of the road on garbage day, but Germanic countries tend to be strict about keeping dead appliances in the same cans food waste & wrap goes in.
 
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