RE: CBM 710: Replacing Power Supply - Help Needed

If the PSU is overloaded, wouldn't it be sensible to try powering the machine on with the load reduced i.e. the drive(s) disconnected or the 8088 board removed?

Chris.

-----Original Message-----
From: Mia Magnusson <mia@plea.se> 
Sent: 14 April 2018 20:37
To: cbm-hackers@musoftware.de
Subject: Re: CBM 710: Replacing Power Supply - Help Needed

Den Sat, 14 Apr 2018 19:12:25 +0200 skrev Michał Pleban
<lists@michau.name>:
> Hello!
> 
> Mia Magnusson wrote:
> 
> > Or you could repair the broken PSU. Unless a TDA1060 / NE 5560 or 
> > some replacement for the BUV48A/BUV47A power transistor is hard to 
> > get, there aren't any parts that's likely to be break and hard to 
> > get a hold of.
> 
> I replaced the PSU with one from another 710 today but after a few 
> hours of work, it died too. This is starting to be really annoying.
> Maybe the PSU doesn't like my setup (710 + 8088 card + internal
> floppy) which generates too much load for it?
> 
> Anyway, both PSUs died in the same way, and now exhibit the same 
> behaviour. When I turn it on, there is power for about 1/2 of second 
> (I can see the LEDs of the floppy drive going on for this time, then 
> going of), then the power goes out. What could cause something like 
> this? I am unfortunately completely clueless with regard to switching 
> PSUs.

Not sure how this one works, but in general switch mode PSU's sense if they are overloaded and shuts down, either immediately or shortly thereafter.

It could also be that when the disk drive wakes up it tries to spin the motors which just hits the limit of what the PSU can handle.

A recap of everything involved seems like a good idea. But maybe there is a reason for the 700 series never were sold with disk drive buildt in?

With all that extra it's probably a better idea to use a new stronger PSU.

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