Peavey Tour 450

[gkp5569]

Hi all,
First post, i have a Peavey tour 450 bass head in for repair, it has no power but all the LEDS are dimly lit. I am having trouble nailing down the fault. something is draggging the power supply down. one thing that i did find unusual is one of the power transistor heatsinks has -40 volts on it. i have never seen this in any equipment i have ever worked on. the circuit diagram shows that this is correct but it is only on one side of the two transistor banks.

does anyone have any experience with this equipment.

P.S this is a warranty job but peavey dont want to replace the whole board

cheers
Gary

[Enzo]

Are you a PV warranty repair center? Most factories are not interested in having their service centers just toss boards into amps.

I would have thought both heat sinks would be hot, not just one. No +40 on the other?

Isolate the problem.

What powr supplies are present and what are absent? There are the low voltage supplies - +/-28VDC, and they supply the pair of three terminal voltage regulators making +/-16VDC. Got any of them? Your LEDs run off that supply. And in many cases where all the LEDs in something are affected, it is many times due to a missing powr rail. if you ever service a mixer and all the peak lights are stuck on, look for a missing 15v rail.

You got -40, is there +40 anywhere? Look on the main bridge or filter caps.

Note, this is a flying rail amplifier, so the power supply caps are not referenced to ground, other than through the speaker load.


Y0u say something is dragging down the power supplies. If that is the case then the unit ought to be drawing TONS of current from the mains. And getting real hot. Monitor the mains current. What does it draw? I'd expect maybe 30 watts idle. Ball park. You get a LOT more than that, and I believe your dragging down idea. You get low draw, and I think the power supply is just missing in action, or dragged to one side, not dragged down.

But without that answer, let me try this. First, as wonderful a company as PV is to work with - they are head and shoulders above the others in my book - they have the annoying habit of leaving the mains wiring out of a lot of schematics. SO start at the start. Is there a 120/240 switch? Is it on 120? assuming you are in the USA.

I don;t know what the mains fuse is, but I do see two 5 ohm thermistors in series with F3. Is that intact, or is it only used on 240v models? Bottom line is this - is mains voltage getting to the power transformer primary?

If so, are the secondary voltages present? There are a pair of 1A fuses for the low voltages. Since they make +28VDC, I have to assume the AC there is about 20 VAC per side, or about 40VAC CT for the winding. That CT is grounded. AMp won;t work without the low voltage rails.

Likewise the high voltages. ther are two HV windings, apparently sharing a CT. Lets just call it a winding with partial voltage taps. Each has its own bridge. The larger one is switched in and out by relay S2, which is controlled by the U9 circuits. U9 and friends sense the output. Note the center tap of that winding does not go to ground. And until the speaker relay closes, it doesn;t get to the speaker either. So don't measure AC volts to chassis, measure across the windings, and from CT to the ends. Got AC? I have no idea what the voltage is, but if you are getting 40VDC, there has to be at least 30VAC somewhere. ANy missing AC from the transformer is a problem.

Let's say the transformer is making all the AC voltages. Is there DC ACROSS the +/- terminals of the bridge? Note the DC termionals of the bridges are in parallel, so it doesn't matter which you use. You could also measure at the main filters - what is across each, NOT what is to ground. VOltage to ground matters, but not just yet. If it is not convenient to get under those filters, there is a 5 watt 4k R121, R122 in parallel with them. Whatever is across the resistor is across the cap. is ther good DC across each. I don;t know what it should be, but the two should be the same. When S2 engages, the voltage would go up there as the larger bridge takes over. But for now we'd be happy with just the lower bridge working.

Now measure each rail to ground. That would be the collectors of the output transistors, and I think that should be on your heatsinks. You got -40 on one, and zero on the other? Is ther 20v across each of those resistors? If that is so, then the whole high voltage rail system is pulled to one side.

The heatsink without voltage, is it shorted to ground? Or showing low resistance to ground? A shorted or driven output transistor will haul the rails to one side without blowing things up. One advantage of flying rail amps - also called grounded emitter amps.

If it were mine, I'd skip over most of that and check the output transistors for shorted first. That takes a few seconds. if none are shorted, then go through the troubleshooting. DOn;t tell yourself it CAN'T be a shorted transistor - or can;t be anything else for that matter - because it can. never think up reasons not to check something.

And remember, at least for test purposes, you only need one of the three output transistors on each side for the amp to function. It can;t put out full power that way, but it can function. SO if you find a shorted output transistor in a row of three, remove it. Then operate the amp on the remaining ones to see if everything else is OK.

[gkp5569]

thanks for the reply enzo,

firstly no i am not a warranty centre, as i am in a remote area (darwin australia), the local music store sends me equipment as it is easier then sending away for repair.

thanks for all the info there are a few things to try there so i will keep you posted how it goes

Cheers
Gary

[Enzo]

Well, good luck. I do service for a number of local dealers here. I understand.

You do realize that American amps must be operated upside down in Australia, don;t you?

I am happy to help, but if you want another opinion, Gene Ford at the factory is a helpful guy, and you can contact him at gford@peavey.com if you have any real technical questions about repair of their products

[Duc]

I found your conversation through a search I did which was very helpful especially the info's from Enzo! I have a 450 with a fault of no output, the last large relay that feeds the speaker output does not closes. Everything looks to work fine, I mean no protection led lights just the blue of the power on lights up. I only found that the 7815 regulator has to be burned... anyway it look be complicated issue and the whole circuit design is complicated! I do servicing from time to time and this happens to be the amp of my brother friend out of warranty of course. All I ask is if someone knows where can I find schematics or even better a repair/service manual that of course I am willing to pay for, I can't find any of these in the net anywhere! Any advice I would appreciate a lot, thanks!

[Chuck H]

You should contact Peavey for schematics and manuals. They have always been very, very nice and helpful IME.

Chuck

[Enzo]

Email customerservice@peavey.com and ask for the schematics for your amp.


Most Peavey schematics are not floating around the internet because the company wil send them to you direct upon request.

[Duc]

Fixed

Thank you for your replies; the gentleman from Peavey was indeed very helpful and sent me the schematics that without them I couldn't ever fix it. The 7815 regulator was blown and let 30 volts pass through that fried some zeners and opamps. Although I had located the faulty zeners there was no way to identify them visually since the numbers printed on correspond to nothing (SMT). At last 15Volts 1.5W were the magic numbers. Anyway thanks again to all.