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Olivetti M24 Power on led

M

mamaroma

Member
Joined
Dec 1, 2022
Messages
18
Location
Italy
Hi everyone,

I took two M24 and the led does not turn on.
I find a voltage of 5V, is it correct?
Are there 5V green LED?
I can't find any information about it.
I could put a standard led with a resistor of about 300 ohms it should be fine.

Thank you
 
Hello, there are many technical manuals which can help you.

AT&T 6300 Shrine - Troubleshooting

Have a 6300 that won't boot? There is a troubleshooting section in the Service Manual, so start there. There have been a few threads over on the VCFED forums that cover trying to troubleshoot and repair the
sites.google.com sites.google.com

You should specially study the "Theory of operations" and the "Service manual". You also find the complete circuit diagrams.

You should also consider buying one of these: https://www.ebay.com/itm/183904562707
The M24 outputs diagnostics codes over the parallel port, before it starts to output messages on the monitor. While that, the original keyboard(s) have a LED blinking. If all of that does not happen something very basic is bad.

Here you'll find the codes: http://www.vcfed.org/forum/showthread.php?54605-How-to-read-parallel-port-POST-diagnostic-codes

(Note: AT&T 6300, Xerox 606x, Logabax Persona 1600 are the same rebadged Olivetti M24 machine, so all mentioned manuals match.)
 
Just to state the obvious: there are no "5V LEDs", but it's normal to measure 5V when the LED is broken/not connected, since without the LED no current is drawn - hence no voltage drop across the series resistor, so you measure the full 5V supply voltage. Depending on the replacement LED you may still need to add an additional series resistor, since modern LEDs usually require less current (or may otherwise get too bright, compared to the original).
 
Thanks to all,
in the end I put a green led with a 150 ohm resistor and the light is slightly lower than the original one but I can't go any further, so I already have a 2.2v output.
I cleaned and checked the two machines and they are in perfect working order.
One has two floppies and bios 1.1 with low serial about 150.000, I removed the battery at a loss.
The other has floppy and 20mb hd, bios 1.36 with very high serial, the battery still seems in good condition. I was thinking of keeping bios 1.1 and only updating 1.36 to 1.43
 
Hi, hope that you'll find. I've totally restored a logabax persona 1600 ( recapped power supply, resoldered all the videoboard, recapped isa board, serviced fdd and screen, changed battery and all). Worked fine. It has a 8087 and a netword card with drivers ! yes ! i was only searching a SCSI card to connect a syquest 44 to have multi os and to do some development...

Until the power supply die again (perhaps fuse ...)

Anyway some photos (sob)... :cry:
 

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Great job, you did so much to bring him back to life.
I have recovered the third M24, they are being restored, unfortunately they have removed some pieces.
I also recovered a cannibalized M280 without video card and floppy drive, I fixed the power supply and the voltages on the motherboard are all correct but no sign of life, the power led lights up but no beeps or video signal.
The control LEDs on the motherboard are all off.
The processor heats up so the voltages are there.
I don't know what else to check. 😭
 
Thanks !
I really like to restore computers (and analog tapes recorder too :) but the logabax was very tricky. The videoboard have some ker capacitors half dead, and some big wires are connected directly on the videoboard. There were a lots of bad contacts and the picture has a lots of glitches and the memory was not stable.
I decided to resolder all the card and it's not the same.

Again, the mainboard has lots of old caps and i decided also to change all, and i do not regret !
For my power supply, i'll test the fuse, because i've recapped all the power supply. Afterward maybe it could be some rectifiers or kind of. They are expected to be eternal, but my humble experience show me that they can sometime be the problematic circuits.
For my studer a80 (see my avatar) the problem was a graetz bridge rectifier, you know the one which should be immortal lol

For the 286, i did not know this beast, but i've found a video of a person who restore one, if it can either help you or give you some ideas.
(but as i see, the motherboard seems as complex/tricky as the logabax :)


But you know, i'm very angry about the power supply of my logabax ... the network card seemed to work and i made a XT-IDE and was about to (try to ) find a 8 bits SCSI or a 8/16 one....

Anyway it will be another challenge.
Regards.

Oh by the way, i remember that my logabax absolutely refuse to display a thing/correctly start without the 360 Ko drive connected !!! could it be that for yours ? Maybe you could add some videoboard as on the 286 i assume that the videoboard is not proprietary as the logabax.
 
I tried putting a working 16bit video card and no floppy disk but the result doesn't change. Even leaving only the motherboard the PC does not emit any error sound. Yes, I confirm the card is really too complicated for me, it could be the processor or the bios but I have no spare parts to try.
 
I think that somedays you'll find some spare. just wait ! Olivetti are tricky but pretty cool machines.

For me it was really tricky, because i started as always to test the motherboard without floppy and hdd connected : only some visible flybacks on the screen and no boot.
And at the end as i was able to put the computer "on a shelf", i connected the floppy drive and it started (no floppy disk, just connect the drive).
Best regards.
 
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