Marshall AVT100 Burned Resistor - diyAudio
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Old 21st June 2011, 04:26 PM   #1
yustech is offline yustech  Malaysia
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Default Marshall AVT100 Burned Resistor

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Power Amp module pic.
Hello great people,I have this new version of the Marshall AVT100 that need repair.
Can anybody that has repair this model tell me the value of R23(burned).
or better anyone with schematic that would help me..
Thanks
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Old 21st June 2011, 04:54 PM   #2
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Had to look it up---- "Marshall AVT100 100W 1x12 3-Channel Combo with DFX. 100 Watts of Power plus 16 effects!!" Well looks like there are getting 100 watts out of two devices but it needs forced air cooling so typical Marshal fashion they are runnng the "sooooot" out of it. Looks like you have it apart, so now is the time to check the output devices because Ill bet they go by by. Post the numbers on the power devices. The problem with new equipment is that the manufacturer dosen't let the schematic loose on the public for some period of time. Is this your amp? or are you in the repair biz?
While we are here, what is Marshal's policy on shcematics? can you buy them? I'll bet you have to be an authorized repair shop to get schematics for the new stuff.
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Old 21st June 2011, 05:06 PM   #3
yustech is offline yustech  Malaysia
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I am the repair busines,I am not keen to the let my client be slaughtered by the authorized service centers.I am qualified to repair and don't any manufacturer dispute this.
My moto is I don't support greedy manufacturer.haha

Help anyone??please.
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Old 21st June 2011, 05:17 PM   #4
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Well Google is a wonderful thing. Sanken Electric SAP16 Transistor And here is a thread on repairing a HI FI that uses the same outputs.
Help Troubleshooting a blown amp (SAP16)
I suggest you check check those transistors for shorts, and pull the burned resistors loose,. try to measure the value with a meter. Even though they are badly burned, you might be able to figure out what they were.
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Old 21st June 2011, 05:42 PM   #5
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So mabe this amp design is not so new. Like 1999 2000 vintage. In this thread they post some schematics, but I think Marshal made a version with a diferent output section.

Marshall AVT100 Schematic

The schematics shown here are for the right model, but it calls out a TDA7293chip amp for the power section -- Id be tempted to look for just the power amp assembly for sale.
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Old 21st June 2011, 08:29 PM   #6
yustech is offline yustech  Malaysia
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Quote:
Originally Posted by firechief View Post
Id be tempted to look for just the power amp assembly for sale.
I know what youre thinkin,..wanting to make guitar amp ei?
I am thinkin the same too...haha
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Old 21st June 2011, 09:53 PM   #7
Enzo is offline Enzo  United States
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The TDA7293 module burnt up too often, they designed that small discrete power amp in its place. Look for the schematic for AVT100X or AVT150X. The X version has the later power amp.

R23 is 33 ohms.

Resistors do not burn up by themselves. I would wager my lunch money that TR9 is bad, and possibly TR10 as well. And it would not surprise me if other parts were bad.
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Old 21st June 2011, 10:01 PM   #8
yustech is offline yustech  Malaysia
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Thanks Enzo,I suspect it too,thing don't just burn out by it self,just need be sure about resistor so I don't gamble and ruin it some more,thanks for the tip.
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Old 8th July 2011, 04:57 PM   #9
yustech is offline yustech  Malaysia
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I have measured the burned resistor,and it read 180ohm,feeling unsure then I have email Marshal through their site referring to technical dept.Still waiting for their reply and would see at this case to judge their corporation and support to 3rd party guitar tech like myself.
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Old 23rd July 2011, 02:25 PM   #10
Gilgy is offline Gilgy  United Kingdom
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Quote:
Originally Posted by yustech View Post
I have measured the burned resistor,and it read 180ohm,feeling unsure then I have email Marshal through their site referring to technical dept.Still waiting for their reply and would see at this case to judge their corporation and support to 3rd party guitar tech like myself.
I know from experience that Marshall will tell you absolutely nothing. They'll just tell you to take the amp to an authorised repairman. UK manufacturers are very paranoid about giving tech advice to non-qualified people and Marshall wouldn't even advise me if JJ EL34 tubes were too tall to fit into a Marshall 50/50 power amp.
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