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tv1010101
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14/09/2020 8:58 am  

Thanks @frocesterbill @rocknroller912

I've no idea how old the amp is, but I'd say "a fair few years".  However, it's in good condition, so it's not had a hard life.  There's no signs of external damage, not even scratches, on the cabinet, so I think damage caused by it being dropped are unlikely.

I'll check over the electrolytic capacitors and see if I can spot any dodgy looking ones.

PlanA is still favourite (the cab & speaker were the only reason that I grabbed it when offered to me), but I just don't like binning stuff when it might be a simple fix!  Though, if I fix this, then I'd have to make another cab for a different speaker ...

 

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tv1010101
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14/09/2020 1:15 pm  

@frocesterbill @rocknroller912

Couple of pics of the innards ...

I think this is the main amp board (the other board hosts the various inputs & controls from the front panel of the amp.  Nothing obvious blown or burnt.  I checked the fuse, which was good too.

20200914 124511

However...

See the two large caps, bottom of the board, next to each other?  Nothing visibly wrong with them, but to the right of them, there's another smaller one (under the red (speaker) wire.  Immediately above that smaller cap, is a small black component that's got a metal side to it.

Closer-up pic;

20200914 124606

I'm guessing that component ("IC27") is doing some fairly critical function.  It was bent backwards, and the metal edge was touching the side of the blue cap (C181).  Might that have caused the problem?

I'm also guessing that perhaps the speaker cable was pushing on it slightly, causing it to bend.  Maybe that pressure was enough to cause the original hissing/buzzing sound, and - when it finally bent too far - then caused the major drop in output power?

To finish-up with my guessing, should I (a) take the circuit board off the backing board and check the solder joints (in case, having been bent, that component is not properly soldered onto the board), or (b) just plug the amp in and (carefully) see what happens?

 

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Bill Flude
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14/09/2020 4:38 pm  

That component (IC27) looks like it might be a voltage regulator - that is a more recent amp than the one I found a schematic for - looks like it has DSPs for effects an poss amp models - bung a picture of the front panel up if you get a chance...

 

Measure once........
Measure again.........
Sod it - make tea!


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tv1010101
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14/09/2020 4:55 pm  

D'oh!  It's going to help if I manage to get the amp model correct.  Sorry @frocesterbill.

🙁

Cube 40 gx.

 

20200914 164555

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Bill Flude
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15/09/2020 9:51 pm  

Valve amps are quite simple circuits, far fewer components than a solid state amp.

Some have point to point wiring - the main components (valves, transformers, controls) are bolted into the chassis and the rest of the components are arranged to connect the fixed bits together.

Some have the main components bolted as in point to point and the rest of the components on tag or turret boards - the board is an insulating material with carefully arranged tags or turrets as nodes to solder components to with wires run from tags to the fixed components.

The final variant has printed circuit boards with some or all of the components mounted on them.

It is worth tracking down Uncle Doug on You Tube - he repairs and restores amps - you won’t find Uncle Doug working with amps with PCBs but the other two variants feature - he is worth a watch.

 

Measure once........
Measure again.........
Sod it - make tea!


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tv1010101
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16/09/2020 7:39 pm  

Quick update @frocesterbill @rocknroller912 -

After a bit of fiddling with the innards of the amp, I thought I'd give it a go (what's the worst that can happen) ...

Now that UK Power Networks have been out and fixed everything and got power restored to the rest of Norfolk I can report that ..

 

THE AMP LIVES.

 

(the bit about UK Power Networks was a joke).

All I did was take it apart, straightened that component that looked like it had been bent backwards and was making contact with the Capacitor next to it, so that it was no longer bent backwards ... then I connected the guitar & power, switched on and ...

It just worked!

Everything seems to be functioning normally.  Plenty of power/output.  I'm now an amp-fixer.

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Bill Flude
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16/09/2020 10:20 pm  

Well done that man!

 

Measure once........
Measure again.........
Sod it - make tea!


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Deej
 Deej
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17/09/2020 2:28 pm  

All I did was take it apart, straightened that component that looked like it had been bent backwards and was making contact with the Capacitor next to it, so that it was no longer bent backwards ... then I connected the guitar & power, switched on and ...

It just worked!

Was that good luck or good management...either way it’s a lot further than I would have managed to do.. 


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Rocknroller912
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17/09/2020 2:53 pm  

@tv1010101

Great news you have struck another blow against the throw away culture. I hope it's given you the confidence to analyse problems.

Bonus points for the forum as well.


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tv1010101
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17/09/2020 2:59 pm  

Cheers guys!

I just looked at it really.  There were no obviously blown Capacitors.  No obviously dodgy solder joints.  Nothing obviously missing or disconnected.

The only thing that looked "wrong" was that one component which looked bent out of shape and appeared to be touching one of the Capacitors (though not sure why that would have mattered).

Bent it back, and all is - magically - good again.

It's a nice enough little amp - built in FX and amp emulators.

 

The only problems are;

  1. I really don't need another amp (particularly if I'm going to build another amp that I don't need, albeit a tasty valve-y one!)
  2. I now need to build another cab to house another speaker that I was going to cannibalise this one for!

😀

For Guitarists and guitar builders everywhere - guitarmaking.co.uk - The Academy of Guitar Making


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Bill Flude
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17/09/2020 9:53 pm  

The 'mended' amp can be your workshop amp - use it for testing new guitars and paly music while you build...

I have a Micro Cube in my workshop - it is connected to a Jensen 10" speaker as the stock Roland one farts if you play loud and dirty through it but sound really good through the Jensen...

Measure once........
Measure again.........
Sod it - make tea!


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tv1010101
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18/09/2020 8:57 am  

The 'mended' amp can be your workshop amp

Yeah, but I've already got my Marshall stack out in the workshop ...

😆

 

(Actually, the workshop amp is a 1980's vintage 30w tranny combo - "Ohm" - that I've had from new.  That amp has served me well!!)

For Guitarists and guitar builders everywhere - guitarmaking.co.uk - The Academy of Guitar Making


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