Vintage Synth Repair

I got a JX8P which restarts itself after a while and then freezes.

Upon first time it is powered on, it works or for a while, and then
after about half an hour, it restarts and start counting down again,
then stops counting at some number and freezes.

I noticed that the two CPUs are rather hot (but that could be
normal?).
What doesn't seem normal to me is the four 8253 ar also very hot.

They are not at all on my MKS-70.... What could cause that ?
I did took it apart in order to paint (refurbish) it.

Could it be a short ? bad CPU ? any idea ??
It is killer sounding (I sold my other, mint condition one, because
this one sounded better, and that was before I realized it was
bad....)

Thanks !

>I got a JX8P which restarts itself after a while and then freezes.
>
>Upon first time it is powered on, it works or for a while, and then
>after about half an hour, it restarts and start counting down again,
>then stops counting at some number and freezes.

Have you checked the power supply?  Excessive supply voltage could possibly 
cause things to overheat and crash.

Good idea,

I'll replace the large caps and check voltages. To the best of my 
knowledge the volteages where ok... but I'll check it again.


--- In vintagesynthrepair@yahoogroups.com, "Scott Nordlund" 
<gsn10@...> wrote:
>
> >I got a JX8P which restarts itself after a while and then freezes.
> >
> >Upon first time it is powered on, it works or for a while, and then
> >after about half an hour, it restarts and start counting down 
again,
> >then stops counting at some number and freezes.
> 
> Have you checked the power supply?  Excessive supply voltage could 
possibly 
> cause things to overheat and crash.
>

On Sunday 06 August 2006 04:19 am, gil_we wrote:
> I noticed that the two CPUs are rather hot (but that could be
> normal?). What doesn't seem normal to me is the four 8253 ar also very hot.

How long does it take before this problem shows up?

First thing I'd do is check the power supply voltage,  and see what you have 
there,  it sounds to me like it might not be at the proper level.

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

It takes about half an hour.

I'm not at all sure it ws there before I took the boards apart and 
painted the machine. 

To make sure it is not a short caused when assembling the entire unit,
I connected ONLY the main board voltage line to the PS and it still 
got heated as well.



--- In vintagesynthrepair@yahoogroups.com, "Roy J. Tellason" 
<rtellason@...> wrote:
>
> On Sunday 06 August 2006 04:19 am, gil_we wrote:
> > I noticed that the two CPUs are rather hot (but that could be
> > normal?). What doesn't seem normal to me is the four 8253 ar also 
very hot.
> 
> How long does it take before this problem shows up?
> 
> First thing I'd do is check the power supply voltage,  and see what 
you have 
> there,  it sounds to me like it might not be at the proper level.
> 
> -- 
> Member of the toughest, meanest, deadliest, most unrelenting -- and
> ablest -- form of life in this section of space,  a critter that can
> be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet 
Masters"
> -
> Information is more dangerous than cannon to a society ruled by 
lies. --James 
> M Dakin
>