Hello DIYaudio forums,
Working on a repair of an unknown malady in a Marshall AVT 50H Valvestate head.
A buddy of a buddy of mine gave me this amp to repair because they were going to throw it away, it would be nice to bring it back to the realm of the playing. Needless to say, he didn't know what was wrong with it, and neither do I!
When the head is powered on, there is a noise that emanates from the head that kind of sounds like a lawn mower in the neighbor's yard. It is coming from the amp itself as there was no speaker cab hooked up to it (I believe this is fine for a solid state amp, yes?).
Here's a video of the phenomenon - Strange Whirring Sound From Amp Head! on Vimeo
My guess is that the power transformer is suspect, but it looks OK on the inside. I'm not going to do much else with it until the mechanical noise that occurs when powered on is identified.
Any help would be greatly appreciated, Cheers!
Working on a repair of an unknown malady in a Marshall AVT 50H Valvestate head.
A buddy of a buddy of mine gave me this amp to repair because they were going to throw it away, it would be nice to bring it back to the realm of the playing. Needless to say, he didn't know what was wrong with it, and neither do I!
When the head is powered on, there is a noise that emanates from the head that kind of sounds like a lawn mower in the neighbor's yard. It is coming from the amp itself as there was no speaker cab hooked up to it (I believe this is fine for a solid state amp, yes?).
Here's a video of the phenomenon - Strange Whirring Sound From Amp Head! on Vimeo
My guess is that the power transformer is suspect, but it looks OK on the inside. I'm not going to do much else with it until the mechanical noise that occurs when powered on is identified.
Any help would be greatly appreciated, Cheers!
> sounds like a lawn mower
It's got a fan. Loosen the covers and carefully stick your head near there, you will find it. Maybe unbalanced with dust. Maybe a mouse tail caught in it. Maybe frame bent so the blades rub.
Marshall AVT50 Noisy Fan
Amplifier Fans
Appears to be 60mm and 24VDC.
Fans of this type can be stalled for diagnostic. Shove a pencil in the fan, power-up. If it is now silent, the fan is for-sure your "lawn mower".
It's got a fan. Loosen the covers and carefully stick your head near there, you will find it. Maybe unbalanced with dust. Maybe a mouse tail caught in it. Maybe frame bent so the blades rub.
Marshall AVT50 Noisy Fan
Amplifier Fans
Appears to be 60mm and 24VDC.
Fans of this type can be stalled for diagnostic. Shove a pencil in the fan, power-up. If it is now silent, the fan is for-sure your "lawn mower".
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PPR,
It was the fan indeed! I considered that when I opened it up as I did not know there would be a fan there, but sure enough that's making the aforementioned noise. Now just some lube and cleaning of the pots and it should be good as new 🙂
It was the fan indeed! I considered that when I opened it up as I did not know there would be a fan there, but sure enough that's making the aforementioned noise. Now just some lube and cleaning of the pots and it should be good as new 🙂
Cleaning and lubricating is a temporary fix.
A new fan would be better. Be carefull that the screws are isolated from the chassis.
Some versions have the heatsink carrying a voltage (forgot wich one) and hence have plastic shims and covers to isolate it from the chassis.
And if you change the fan, I believe it's 10mm thick, a 20 mm will fit to.
A new fan would be better. Be carefull that the screws are isolated from the chassis.
Some versions have the heatsink carrying a voltage (forgot wich one) and hence have plastic shims and covers to isolate it from the chassis.
And if you change the fan, I believe it's 10mm thick, a 20 mm will fit to.
all the avt and mg series marshalls suffer from these fan problems .I`ve always cleaned and oiled them as part of a service or refurb , and told customers to keep the fan dust free with a small brush . A small % fail again , maybe 1 in 10 , but are usually full of dust and dog / cat hairs !
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