Just to jump in - when you say you get just over 8VDC on the anode side, you don't mention what the other side of the measurement is. For troubleshooting not assuming a ground is there until establishing that it is, is a good habit.

So forgetting ground connections for a second, what I do to see if a full wave bridge rectifier is working, (the kind with four lead) is :

1) Set meter for AC,  Measure directly across the AC inputs, these have an Anode and Cathode each connected and also connect to the transformer
        - You should see the transformer voltage.  Again this is between the AC IN leads only and not measured to ground.

2) Set meter to DC.  Measure across the rectified outputs, these are two leads usually marked with "+" and "-" on packaged rectifiers.  Measure directly across the outputs, don't ground the meter at this point.  You should see some kind of DC, none at all would be indicative of a dead short (heat and fuse) or two diodes open in the rectifier. Good time to look for little fuses nearby that may be blown.

If this is done with discrete diodes then a little conversion is needed for visualization.  http://en.wikipedia.org/wiki/Diode_bridge has a pretty good picture of a FBR, note that the "+" side is where two cathodes (bands) are connected and the "-" is two Anodes.  Any junction that has an Anode and a Cathode is an AC input.  Measure directly between the junction of two Anodes to the junction of two Cathodes.

You may be way past this, just thought I would visualize since I missed an email or two.

Bil


-----Original Message-----
From: owner-cbm-hackers@ling.gu.se [mailto:owner-cbm-hackers@ling.gu.se] On Behalf Of Philip Lord
Sent: Tuesday, August 11, 2009 10:01 AM
To: cbm-hackers@ling.gu.se
Subject: Re: Dead PET 2001

Unfortunately this is not the case.
thanks though.

On Aug 11, 2009, at 10:03 PM, Bil Herd wrote:

> Possible the meter is in AC mode?
>
> -----Original Message-----
> From: owner-cbm-hackers@ling.gu.se [mailto:owner-cbm-hackers@ling.gu.se
> ] On Behalf Of Philip Lord
> Sent: Tuesday, August 11, 2009 8:31 AM
> To: cbm-hackers@ling.gu.se
> Subject: Re: Dead PET 2001
>
> Update:
> With the red leads detached from the capacitor I tested the voltages
> again this evening.
> Where as before I was getting over 8VDC, now I'm only getting 0.5VDC
> on the cathode side of the diodes...very strange. I wish I knew what
> was going on.
> Maybe it's time to start by removing the diodes and testing them.
>
> Phil
>
>
> On Aug 10, 2009, at 3:14 PM, Philip Lord wrote:
>
>> Thanks William,
>> I did as you described.
>> I removed the red wires from the capacitor and re-measured the
>> voltages on either side of the two diodes.
>> As before I get just over 8VAC on the anode side, but now I get
>> just over 8VDC on the cathode side.
>>
>> I also tested the large capacitor using the ohm meter on my digital
>> multimeter. It starts at Zero ohms and slowly rises.
>>
>> I apologies for my lack of electronic knowledge, and once again ask
>> what I should try next? Hopefully we are narrowing down the problem.
>>
>> Cheers again
>> Phil
>>
>>
>>
>> On Aug 10, 2009, at 1:07 PM, William Levak wrote:
>>
>>> On Sun, 9 Aug 2009, Philip Lord wrote:
>>>
>>>> oops...Please excuse my bad typing...what I mean to say was:
>>>>
>>>> Yes, I admit I was checking the voltage on the inside of the
>>>> diodes with my multimeter (digital) set to AC. I just rechecked
>>>> with it set to DC and the reading is still in the millivolt range.
>>>> If the diodes are indeed the culprit, I find it strange that both
>>>> diodes would be open?
>>>> As for the J8 connecter, it basically looks new, no dirt, or
>>>> burning at all.
>>>
>>> You said the fuse blew several times.  That would be enough to blow
>>> the diodes.  Disconnect the red wires from the capacitor, and check
>>> the voltages again.  Also check the capacitor for shorts.  If you
>>> don't have a capacitor tester, you can use an ohm meter.  The
>>> resistance should start at zero and build up.
>>>
>>>    Message was sent through the cbm-hackers mailing list
>>
>>
>>     Message was sent through the cbm-hackers mailing list
>
>
>       Message was sent through the cbm-hackers mailing list
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