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Troubleshooting an Alesis A6 Andromeda - No Boot Keyboard Synthesizers
Old 2nd April 2019
  #391
Gear Maniac
 
M.Retra's Avatar
Quote:
Originally Posted by Genesis92 View Post
my opinion is to choose the industrial grade for the RAM.
I'm always using the industrial chips for my design.

about the PSU we cannot be sure but when I'm working on old synth PSU or when I replace the coldfire from the A6, i'm allways adding a transorb diode in the +5V / +3.3V supply rail. (attached picture is an A6)
it's cheap and can save the life of expensive / obsolete components if the PSU fail.

The transorb diode absorb energy (short the supply) when the voltage go over its trip point.
i'm allways using this rule when I'm designing power supply units for our products and it's very rare when components are killed by over voltage.

I remember in production, a guy has made a short between the +12V and 5V on one of my design. the system has blown the input fuse, the 5V transorb where in short circuit (its failure mode) but when the transorb was replaced all was working like a charm the computer board was alive.
By "transorb" you mean voltage suppression diode. I never heard of the term "transorb" or "transabsorb" rather, which is a mouthful!

Looks like you have used part number SMBJ5.0, which as a min breakdown voltage 6.4V. When 6.4V is reached, the diode shorts the power supply rail to ground.

Furthermore, it appears you've put it on the output side of the linear regs. Though linear regs are some of the most hardy devices ever made, putting the diodes on the output side would protect for failure of the linear reg and the main PSU, which is more likely. Not a bad circuit addition!
Old 2nd April 2019
  #392
Gear Head
 
Genesis92's Avatar
yes it's an SMBJ5.0 and I'm using SMLVT3V3 for the 3.3V supply line. (other parts are available for higher power like 1N5908)
they have several names :D transorb, transil :D
the breakdown voltage is 6.4V but even if it's a high value most of circuits can survive to a peak of this voltage for a short time (the time to the transil to completely short the supply).

The diode must be installed on the regulated voltage supply line of the chips to protect so the best is at the output of the linear regs and at the nearest point of the current feed (to immediatly short supply in case of failure). If the trace is too long between the feed point to the diode the parasitic inductance can kill the chips installed before the diode

linear regulator are reliable yes but some old ones can becomes instable (oscillation with higher output voltage) when the filtering cap at the output is too old and does not reach the minimum stability capacitance (look at my XV5080 topic )
XV-5080 "static noise" solution
Old 4 weeks ago
  #393
Here for the gear
 

hi all !
Andy owner from Italy here, I've been with my A6 since 2001, and still think it’s the most enjoyable absolute weapon in subtractive synthesis.

First of all, let me express how extraordinary I think this thread is and so are the guys contributing to it.
I keep coming back periodically and got emotional each time when reading about mysteries solved and resurrected Andromedas.
( … and also when an original lead designer and programmer chimed in )

Now, as you would imagine, I’m also here because my A6 is down, and I’m not ready yet to sell it for spare parts. I’ll be detailing in my next post what is happening to my synth.

I know a capable tech that I trust, but I can’t ask him to leave everything else and dive into the A6 architecture and troubleshooting,
so as an average a6 owner without much electronics knowledge, I feel it is important to keep on record how much this thread can help anyone in guiding his trusted tech to diagnose and hopefully resurrect a non booting A6.
Old 4 weeks ago
  #394
Here for the gear
 

So My A6 is not booting ...
I think mainly due to an innocent bad joke:
someone put the LCD contrast at max, so I thought it was suddenly dead,
and started switching it on and off a lot of times,
trying to the get SB powerup modes, diagnostic mode etc.

When I found about the LCD, I saw it was not booting anymore :
- Normal boot displays a6 logo, inverts colors, flickers once and then hangs
- SB boot into Diagnostic mode is ok ( Slow ram test also says ok )
- SB boot for soft reset / hard rest / OS or Bootloader update are available but hang when I press Store button
- behaves like in Genesis92 videos.

As far as I can understand :
- FPC is OK, and controls and buttons seem ok from diagnostic mode
- Main CPU seems to at least be able to execute the first boot sequence instructions (logo color inversion)
- problem should be located in the main board.

I took it to my trusted tech, and I suggested to perform this troubleshooting step, taken from the SM and from this thread :
- reseated ribbon cables,
- checked PSU voltage at the main board
- checked crystals on the main board ( replaced M1 30MHz crystal )
- checked CPU and RAM pins for shorts
- looked at the reset line
- replaced the ICSI chips ( we used 10ns chips, I hope it is not a problem )
- added the Pull-Up Resistor Fix on Fast SRAM Pin 6

( as an example, I have little idea on how to check a crystal or look at the reset line,
but the tech knew how to do it once I told him what to look for )

Anyway, still no improvement, so if I read the thread correctly next steps are CPU and flash memory replacement.

I’ve ordered this ‎MCF5307AI90B-ND from DigiKey and will handle it to my tech with best hopes
MCF5307AI90B NXP USA Inc. | Integrated Circuits (ICs) | DigiKey

If it still does not boot after CPU replacement, I’ll be looking for flash chips...

Or maybe I should get flash chips immediately and replace them anyway ?
Old 4 weeks ago
  #395
Gear Nut
 

The more you do the more risk there is that you accidentally make things worse. Try the CPU swap first.
Old 4 weeks ago
  #396
Here for the gear
 

Quote:
Originally Posted by bklein View Post
The more you do the more risk there is that you accidentally make things worse. Try the CPU swap first.
ok thanks a lot!
One step at the time is surely the best way :-)
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