[sdiy] Off topic - Alesis AI4 spares ?

dragons dragon.servicing at googlemail.com
Fri Jun 17 23:52:50 CEST 2016


HI,
it is likely that some load would need to be provided on the unused 
power supply rails, as otherwise the switchmode supply might not start 
up. but it is possible that the + - 12 volt supplies might be used on 
just a few ic's and the tracks to these may not be obvious.
Hope you can get things sorted out.
regards Peter

On 17/06/16 22:27, Dave Kendall wrote:
> Hi Steve.
>
> The fuse has blown, and blew a replacement fuse (with lightshow and
> magic smoke). Nasty smell around one of the transformers. None of the
> caps are distorted or bulging, but two caps read very low resistance
> across the terminals. Blown I guess.
>
> I’ve done a bit of tracing of the circuit. There is a 4-pin 0.156”
> connector linking the single PSU PCB to the main PCB.
>
> Pin 2 goes directly to the inputs of a 7805 and two LM317Ts. Pin 2 is
> decoupled to GND on the PSU PCB via a 16V 1000uF cap.
>
> Pin 3 is GND
>
> Pins 1 and 4 are decoupled on the PSU board via 25V 220uF caps with pin
> 1 connected to the + terminal, and pin 4 connected to the - terminal. So
> a ±12 V supply maybe ? (caps rated at double the voltage ?)
>
> On the main PCB, pins 1 and 4 each go through a large (3W ?) resistor to
> GND. Could it be that these big resistors are to provide a load for the
> (unused) ±12V supply ?
>
> If so, that might mean Pin 2 is something like a 5 - 9V supply. Am I
> likely to damage anything on the main board by giving it something like
> a regulated 9V ? I think that a 7805 needs a few V above 5V to operate
> correctly. . .
>
> Sorry for all the questions - the schematics are not available it seems,
> and if it can be got going again with a DC supply that would be
> marvellous. (The unit only handles ADAT and AES / EBU signals - no
> analogue circuits)
>
>
> cheers,
> Dave
>
>> On 17 Jun 2016, at 20:37, Steve Ridley <spr at spridley.freeserve.co.uk
>> <mailto:spr at spridley.freeserve.co.uk>> wrote:
>>
>>
>> Dave
>>
>> Has the supply actually blown up (fuse / smoke / smell / bang) or is
>> it just not starting up?
>>
>>
>>> Hi guys. Sorry for the slightly OT post - I have an Alesis AI4 ADAT
>>> to AES/EBU converter with a blown switched-mode PSU. Can anyone
>>> recommend any repair people who just *might* have either schematics,
>>> or possibly spare parts ? The unit is not supported by Alesis any
>>> more, and they don’t have spares, and won’t supply schematics. In a
>>> conversation with alesis support today, all I learned is that the PSU
>>> outputs 5V (no analogue circuitry on board) and there are 3.3V parts
>>> on board. The guy I spoke with didn’t know much more than that, and
>>> was unable to find out if the PSU board is used in any other products
>>> (he did try though) . Any help or pointers gratefully received.
>>> cheers, Dave
>>
>
>
>
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