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Aria Sinsonido preamp repair

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Re: Aria Sinsonido preamp repair

Postby Dr R » Mon Jun 04, 2018 8:58 pm

Hi again,

Here are better photographs of the circuit board. Top, bottom and edge on. I've taken quite large photographs, so hopefully there is enough detail.

The black stuff is an epoxy gunk, no obvious reason for it that I can see. Removing the board would be desoldering eight wires from the PCB and cutting the battery wires further up.

I wasn't able to make any voltage measurements at lunchtime, but will do so tomorrow. Any other measurements that can be done with a multimeter and a little headphone amp, let me know :-)

Many thanks to everyone who has replied to this. My colleague's comment "What an amazing board - the forum not the circuit" says a lot.

Rich

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Re: Aria Sinsonido preamp repair

Postby James Perrett » Mon Jun 04, 2018 9:19 pm

Is the pot on the right the tone control?
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Re: Aria Sinsonido preamp repair

Postby Dr R » Mon Jun 04, 2018 9:49 pm

James Perrett wrote:Is the pot on the right the tone control?

According to the manual on the Aria worldwide archive http://ariaguitarsglobal.com/wp-content/uploads/Sinsonido-instructions.pdf the tone control is the one on the right looking at the pots end on from the outside, as James suggests.

I'll have to actually plug it in tomorrow and check because I can't remember.
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Re: Aria Sinsonido preamp repair

Postby Dr R » Tue Jun 05, 2018 1:54 pm

Report back from the investment bank guitar workshop. Getting some strange looks at lunchtime now :bouncy:

  • The volume pot is the one closest to the thicker white lead going to the output (marked A on the back), the tone control is the other one (B).
  • Testing with the multimeter showed a voltage out Vout-GND of around 0.5-0.6V when the E string is plucked. Same for both chips, independent of the volume out position.

Checked the pot values. Power disconnected.
Numbering the pins according to the photograph above as
2, 4, 6
1, 3, 5
with 1, 3, 5 closest to the shaft.
Pot A (volume).
  • R12 = 1.96K, regardless of position
  • R13 14 Ohm - 1.1K variable
Pot B (tone).
  • R12 = 1.2K, regardless of position
  • R13 11 Ohm regardless of position

Which rather implies it's the pot that is knackered, unless there's something I'm missing?

Rich
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Re: Aria Sinsonido preamp repair

Postby James Perrett » Tue Jun 05, 2018 2:09 pm

Is it a dual ganged pot and, if so, have you checked the other half (pins 2, 4 and 6?
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Re: Aria Sinsonido preamp repair

Postby Dr R » Tue Jun 05, 2018 2:35 pm

James Perrett wrote:Is it a dual ganged pot and, if so, have you checked the other half (pins 2, 4 and 6?


Are you suggesting that the odd pins form one potentiometer, and the even pins form another, independent but on the same shaft? I hadn't thought of that (probably because of the afore-mentioned 30 year gap). In which case what combinations should I test?
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Re: Aria Sinsonido preamp repair

Postby Hugh Robjohns » Tue Jun 05, 2018 4:36 pm

That would be the usual arrangement, with 2 and 4 being the wipers.

H
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Re: Aria Sinsonido preamp repair

Postby Wonks » Tue Jun 05, 2018 5:02 pm

Hugh Robjohns wrote:That would be the usual arrangement, with 2 and 4 being the wipers.

H

In keeping with DR R's numbering system, that would be 3 and 4 surely?
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Re: Aria Sinsonido preamp repair

Postby Wonks » Tue Jun 05, 2018 5:16 pm

The volume pot is marked A1k, so should be a 1k ohm dual-gang pot with an Audio/log taper (as one would expect for the volume pot), and the tone is marked B1k so should be a 1k ohm dual-gang pot with a linear taper.

So with one of the dual gang pots being pins 1, 3 and 5, and the other being pins 2, 4 and 6 you should get a constant around 1k ohm between pins 1 & 5, and pins 2 & 6. Between pin 1 and pin 3, or pins 3 and 5, you should get a variable resistance that varies either from (near) nothing to 1k, or from 1k to nothing. Likewise with pins 2, & 4 and 4 & 6.

On the tone pot, the resistance from either of the outer pins to the central wiper in the mid-position should be around 500 ohms. On the volume pot, because of the different taper, it should be around 200-300 ohms from one end pin to the wiper, and between 700- 800 ohms from the wiper to the other end pin.

The above ignores any effect of other components being wired across the pots in parallel, which may affect the resistance readings somewhat (difficult to say without a circuit diagram) which could lower the resistance readings, but you should still always see a variation of resistance between the central wiper pin and the two end pins.
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Re: Aria Sinsonido preamp repair

Postby Dr R » Tue Jun 05, 2018 5:23 pm

So to get the full picture I need to check all the resistances
R15, R13, R32, R26, R24, R46 on each pot. (Rnm being the resistance between the pins n&m)
R12 will presumably be nothing to do with the pot, and measuring the resistance of other components on the board.

It looks from the picture that 5&6 are linked on one pot at the back of the board. That would make them ground. So (brain slowly getting there), would that make pins 1 and 2 the Vin for each pickup and 3,4 being the output?

Many thanks for everyone's interest in the problem, and patience!
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Re: Aria Sinsonido preamp repair

Postby Hugh Robjohns » Tue Jun 05, 2018 5:28 pm

Wonks wrote:
Hugh Robjohns wrote:That would be the usual arrangement, with 2 and 4 being the wipers.

H

In keeping with DR R's numbering system, that would be 3 and 4 surely?

Sorry -- yes, well spotted. Typo on my part!

Numbering the pins according to the photograph above as
2, 4, 6
1, 3, 5
with 1, 3, 5 closest to the shaft.

So 3 and 4 are the wipers...
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Re: Aria Sinsonido preamp repair

Postby Wonks » Tue Jun 05, 2018 5:42 pm

Dr R wrote:It looks from the picture that 5&6 are linked on one pot at the back of the board. That would make them ground. So (brain slowly getting there), would that make pins 1 and 2 the Vin for each pickup and 3,4 being the output?

That would be the most likely arrangement, though it is possible that the inputs are via the wipers (3 and 4) and the outputs on 1 and 2.

As the tone control seems to be a simple treble-roll off type, then it could be a passive tone type similar to an electric guitar, where the pot isn't used as a potential divider with all three pins connected, but as a variable resistor, with just two of the pins connected, one being the wiper. The pot controls the amount of high frequency passed down to ground via a capacitor wired in series with it. It may well be an active circuit, but don't be surprised if pins 1 and 2, or 5 and 6 aren't connected to anything else.
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Re: Aria Sinsonido preamp repair

Postby Dr R » Tue Jun 05, 2018 7:56 pm

:thumbup:
Thanks all. That's tomorrow lunchtime sorted
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Re: Aria Sinsonido preamp repair

Postby ef37a » Tue Jun 05, 2018 8:02 pm

My brain hurts.
There are surely tracks under those pots that you cannot see. I think you need to test for S/C links and draw a "net" of the pot wiring.

Are you sure there isn't an SM capacitor rolling around somewhere?

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Re: Aria Sinsonido preamp repair

Postby Dr R » Tue Jun 05, 2018 9:08 pm

ef37a wrote:My brain hurts.
There are surely tracks under those pots that you cannot see. I think you need to test for S/C links and draw a "net" of the pot wiring.
Are you sure there isn't an SM capacitor rolling around somewhere?

Dave.

There definitely are no components knocking about loose, though anything surface mount could have escaped while the guitar was away; there are no gaps on the board I can see where something might have fallen off.
However there are tracks under the tone pot, running from the two .47 capacitors next to it

I am sorely tempted to take Folderol up on his kind offer and post the board to him, but that feels like giving up early!
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