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PS re-cap vs new [message #394879] Sat, 23 May 2020 18:41 Go to next message
Anonymous
Karma:
Originally posted by: wade kemp

Hello all,
I was recently given a un-enhanced //e. When I turn the power on, the led on the motherboard lights, but no beep.

I checked the Voltages on the PS and they are a tad off, is re-capping enough to get that back to speck ?

Thanks
Wade
Re: PS re-cap vs new [message #395028 is a reply to message #394879] Wed, 27 May 2020 02:56 Go to previous messageGo to next message
Michael J. Mahon is currently offline  Michael J. Mahon
Messages: 1697
Registered: October 2012
Karma: 0
Senior Member
wade kemp <wadeakemp@gmail.com> wrote:
> Hello all,
> I was recently given a un-enhanced //e. When I turn the power on, the
> led on the motherboard lights, but no beep.
>
> I checked the Voltages on the PS and they are a tad off, is re-capping
> enough to get that back to speck ?
>
> Thanks
> Wade
>

Most likely, the power supply is fine. The voltages only need to be within
+/-5%.

If you have access to a scope or logic probe, check the clock signal and
the /RESET signal to the CPU (a multimeter will work for that).

If they’re both OK, look to the DRAM, then the $F800 ROM.

If you have another //e, you can swap DRAM, ROM, and other chips to test
whether you can “move the fault”.

--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
Re: PS re-cap vs new [message #395601 is a reply to message #395028] Tue, 09 June 2020 16:32 Go to previous messageGo to next message
Anonymous
Karma:
Originally posted by: wade kemp

Michael,
Using a scope, I find that /RESET just stays low. Clock 0 is fine, but Clock 2 is more of a saw tooth. Any ideas ?

Wade


On Wednesday, May 27, 2020 at 2:56:19 AM UTC-4, Michael J. Mahon wrote:
> wade kemp <wadeakemp@gmail.com> wrote:
>> Hello all,
>> I was recently given a un-enhanced //e. When I turn the power on, the
>> led on the motherboard lights, but no beep.
>>
>> I checked the Voltages on the PS and they are a tad off, is re-capping
>> enough to get that back to speck ?
>>
>> Thanks
>> Wade
>>
>
> Most likely, the power supply is fine. The voltages only need to be within
> +/-5%.
>
> If you have access to a scope or logic probe, check the clock signal and
> the /RESET signal to the CPU (a multimeter will work for that).
>
> If they’re both OK, look to the DRAM, then the $F800 ROM.
>
> If you have another //e, you can swap DRAM, ROM, and other chips to test
> whether you can “move the fault”.
>
> --
> -michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
Re: PS re-cap vs new [message #395602 is a reply to message #395601] Tue, 09 June 2020 17:50 Go to previous messageGo to next message
Anonymous
Karma:
Originally posted by: Frank M.

I have a similar machine with a similar problem that was fixed with a new 6502 CPU.
Re: PS re-cap vs new [message #395634 is a reply to message #395602] Thu, 11 June 2020 11:52 Go to previous messageGo to next message
Anonymous
Karma:
Originally posted by: wade kemp

On Tuesday, June 9, 2020 at 5:50:57 PM UTC-4, Frank M. wrote:
> I have a similar machine with a similar problem that was fixed with a new 6502 CPU.

Thanks, I was going to pop for the enhancement kit anyway. So it's nice to know that MIGHT take care of that problem.

Wade
Re: PS re-cap vs new [message #395635 is a reply to message #395601] Thu, 11 June 2020 20:04 Go to previous messageGo to next message
sicklittlemonkey is currently offline  sicklittlemonkey
Messages: 555
Registered: October 2012
Karma: 0
Senior Member
On Wednesday, 10 June 2020 06:32:51 UTC+10, wade kemp wrote:
> Michael,
> Using a scope, I find that /RESET just stays low.

Until Michael replies, you have a scope, so consult a schematic (use the PAL schematic if it's a PAL //e) and trace where the reset signal comes from. Check out the inputs and outputs of that chip rinse and repeat! ; - )

Cheers,
Nick.
Re: PS re-cap vs new [message #395814 is a reply to message #395601] Mon, 15 June 2020 20:49 Go to previous message
Michael J. Mahon is currently offline  Michael J. Mahon
Messages: 1697
Registered: October 2012
Karma: 0
Senior Member
wade kemp <wadeakemp@gmail.com> wrote:
> Michael,
> Using a scope, I find that /RESET just stays low. Clock 0 is fine, but
> Clock 2 is more of a saw tooth. Any ideas ?
>
> Wade

Well, the 6502 won’t do anything until /RESET goes high, so something is
incorrectly holding it low.

Peripheral cards can do that, so start by removing any plug-in cards.

If that doesn’t cause /RESET to go high, the keyboard is the other source
of /RESET. Try unplugging the keyboard and turning on power. If that was
the problem, the computer will repeatedly run its self-test, flashing
things on the screen and ending (one cycle) with a brief report on the
screen.

The sawtooth shape of Phase 2 could be the result of probe loading. Try a
10:1 probe and see if it looks better. You will need a scope bandwidth of
more than 10MHz to see the waveform depicted as the almost square wave that
it is.

If the appearance doesn’t change using a 10:1 low capacitance probe, then
something is loading the output significantly, but that’s less likely than
a problem in the reset circuit. Fortunately, the reset circuit is quite
simple, so that’s the first thing to troubleshoot. Refer to the schematic
for info on the reset circuit.

Also, don’t overlook the possibility of debris shorting printed circuit
traces. The power-on reset signal on the //e is generated by the IOU chip,
so a failure of that chip could cause the problem.

This could be diagnosed by “lifting” the IOU’s /RESET output pin and
checking that it stays low for about 30 milliseconds when power is applied,
then goes to logic high.

Once you get /RESET de-asserted, the processor, and hopefully much else,
will start to function.

Good luck!

-michael


>
> On Wednesday, May 27, 2020 at 2:56:19 AM UTC-4, Michael J. Mahon wrote:
>> wade kemp <wadeakemp@gmail.com> wrote:
>>> Hello all,
>>> I was recently given a un-enhanced //e. When I turn the power on, the
>>> led on the motherboard lights, but no beep.
>>>
>>> I checked the Voltages on the PS and they are a tad off, is re-capping
>>> enough to get that back to speck ?
>>>
>>> Thanks
>>> Wade
>>>
>>
>> Most likely, the power supply is fine. The voltages only need to be within
>> +/-5%.
>>
>> If you have access to a scope or logic probe, check the clock signal and
>> the /RESET signal to the CPU (a multimeter will work for that).
>>
>> If they’re both OK, look to the DRAM, then the $F800 ROM.
>>
>> If you have another //e, you can swap DRAM, ROM, and other chips to test
>> whether you can “move the fault”.
>>
>> --
>> -michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
>
>



--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
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