Question about Peavey Classic 30112 Tweed

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Howdy, I have the mains light on and the pre-amp valves light up but the power valves wont light up. I've replaced the 10amp ceramic fuse and can hear hum but still no light on the EL84's. The amp was running sweetly and reliably up until yesterday. thankfully it failed at a rehearsal and i have a JTM-45 to work with, but, this is somewhat unusual and I do like the amp for certain gigs. Any assistance in this matter will be gratefully appreciated. Adios Tex

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Since the pilot light is on, the transformer is delivering the heater power.

An educated guess at the problem is a crack on the circuit board or bad solder joint. Since NONE of the EL84's are lit, there is likely a crack or soldering at a circuit board feed-thru.

Should be easy to trace. PLEASE be careful as there is around 400 volts in this amp !!!!!

Posted on Sep 29, 2010

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Hi, my amp just died, i turned it on than the led lighted um and died, now i wont turn on ...


UNPLUG THE AMP
First you need to check any visible fuses either in the plug or on the back of the amp.
If you have an electrical testing screwdriver or meter you can test the fuse. If this sounds like gobbledegook (daft talk) then stop and take it to the dealer where you bought it.
If you can remove the fuse or fuses then replace them if it is obvious they have blown - dark and kinda burnt looking.
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LOW POWER AND CRAKLING


Chances are that one of your tubes (valves) has failed.
If your amp is still in manufacturers warranty take it back to the place where you bought it.
Otherwise you need to identify which tube has gone and replace it. This will entail gaining access to the inside of the amplifier case. BEWARE this can be VERY DANGEROUS if you don't know what you are doing.
IF IN DOUBT TAKE IT TO A REPAIR SHOP
Always disconnect from the mains electricity supply before dismantling.
Once you have got the case off you will need to plug the amp in again and turn it on - you don't need to plug a guitar in just the mains supply. TAKE GREAT CARE not to touch any metal parts.
Look at each of the valves (there are some on the pre-amp stage behind the front panel as well as on the main amplifier chassis) they should all be glowing a nice bright red colour in the middle if they are healthy.
If any valve is not 'lit up' that will be the faulty one. DO NOT TOUCH IT - apart from the high voltage electricity associated with them valves get very HOT.
Turn the amp off, unplug the mains supply and WAIT at least 10 minutes for it to cool down again. Carefully slip the metal retaining spring off the top of the valve and, gripping it with a tissue or soft cloth, gently pull it out with a slight rocking motion. Carefully note down all the numbers and letters on the valve to identify the correct replacement. There are literally hundreds of different valves - putting the wrong one in may cause further damage to the amp.

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No Power at all. Fuse blown-Burn smell from fan area.


You did a lot of damage, and replacing the fuse and trying it has caused much more.

There will be about seven blown parts on the amp and a dozen on the power supply. To give you an idea of the extent, the WHOLESALE parts cost is roughly $50, including the main power supply switchers IGBT's which cost nearly $20 for the pair by themselves.

I have repaired several of these and the larger cousin the PMP5000. It is a lot of skilled work to repair these.

The cause is a marginal insulation between layers of the multi-layer amplifier board. Usually the rearmost amp arcs between the layers. This fries three big switching transistors followed sometimes by a metering resistor and two small surface mounted transistors. A zener diode often goes. The cancer and burned area has to be ground out with a dental drill and new wire replaces the blown circuit traces.

If you are under warranty, take the unit for replacement.

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DO NOT REPLACE THE FUSE !!! You will do more damage.

I just repaired one of these. A small ceramic surface mounted cap very near where the +/- 85 volt connectors plug onto the board blew up.

This left a sputtered mess on the insulating material at the right rear corner of the power supply.

The net parts list of parts I had to replace:

1. Main IGBT transistors on heat sinks. You have to remove the heat sinks to get at the mounting screws. 1MBK50D or equivalent. I used DigKey part APT28GA60BD15

2. One 1N4148 surface mount diode that is for gate drive speedup. D24 and D25. (don't remember which one was shorted)

3. All four driver transistors for the gate of the IGBT's. @ each 2SA1020 (PNP) and 2SC2655 (NPN). These are tall TO92-like transistors and I believe that at least one of these I had to get from Mouser.

4. Transistor T9, suface mount BC856B (PNP)

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7. The 2153 switching reg chip IC1. This chip shorts. It is made by International Rectifier and I believe the full number is something like IRF2153. I had these in stock and not sure of which source I had procured them from... It was from one or the other.

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The repaired unit had to be brought up with a light bulb in series with the line power cord to prevent further damage until all bad parts were discovered and repaired. You will need to take the unit to a shop that is expperienced with the product. The repair cost MAY be pretty high.

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