[sdiy] Off topic - Alesis AI4 spares ?
davekendall at ntlworld.com
Fri Jun 17 23:27:49 CEST 2016
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)
> On 17 Jun 2016, at 20:37, Steve Ridley <spr at spridley.freeserve.co.uk> wrote:
> 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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