[volt-nuts] Subject: Re: Keithley 2001 Multimeter Fault - Update

[Alan Scrimgeour]

I replaced the three tracks I had to cut with relatively sturdy wire, but I 
might use just a little epoxy to anchor things in place where movement might 
eventually cause stressed tracks to crack. What I'll avoid is epoxy bridging 
any adjacent conductors so there's no chance of it causing leakage problems 
if it eventually deteriorates.

Alan

----- Original Message ----- 
From: "Dick Moore" <richiem at hughes.net>
To: <volt-nuts at febo.com>
Sent: Wednesday, March 17, 2010 7:14 PM
Subject: Re: [volt-nuts] volt-nuts Digest, Vol 7, Issue 9


> Alan, if it's possible to just leave the hole in the board, that may be 
> the best solution overall. BTW, Nichicon has always had a very good 
> reputation for quality electrolytics, as have the Japanese suppliers in 
> general. The 2001 is certainly worth the effort to repair. I had a similar 
> problem with a PCB in a Fluke 732A DC Reference. An epoxy coated Ta cap 
> burned up and took a lot of the board with it and then a resistor burned 
> as a result and took more board. I scraped and dug away the carbon and 
> left the board as is -- of course this was not a multi-layer board. Most 
> instruments don't need the sealer protection once in a lab in relatively 
> dry, warm air where they'll be used for a long time. I wouldn't be sure 
> that using the automotive epoxy would be a good idea...
>
> Dick Moore
>
>
> On Mar 17, 2010, at 5:00 AM, volt-nuts-request at febo.com wrote:
>
>>
>> Message: 6
>> Date: Wed, 17 Mar 2010 11:20:37 -0000
>> From: "Alan Scrimgeour" <scrimgap at blueyonder.co.uk>
>> Subject: Re: [volt-nuts] Keithley 2001 Multimeter Fault - Update
>> To: <jfor at quik.com>, "Discussion of precise voltage measurement"
>> <volt-nuts at febo.com>
>> Message-ID: <AE27F40615CE4CA08494C3AD153F4414 at AlanPC>
>> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>> reply-type=original
>>
>> Perhaps only the copper was 'etched', but I can imagine even epoxy being
>> attacked by hot electrolysis taking place right next to it. Electrolysis
>> could produce some very active compounds, depending on the electrolyte 
>> (and,
>> I'm not sure, but in such close proximity to the electrodes there may 
>> also
>> be some extremely reactive short lived species, or is that just Sci-Fi?).
>> But by some mechanism the upper layer of glass fiber in the board was
>> visible before I started digging it away.
>>
>> The excavation is progressing with care. In the centre the damage has 
>> gone
>> right through the board to virtually the other side. Presumably air 
>> cooling
>> stopped or slowed the progress of the damage actually through the very 
>> last
>> layers of the board.  It appears that once the hot electrolysis had begun 
>> to
>> damage the pcb it carbonised and in that conductive state, drew current 
>> and
>> generated yet more heat leading to a chain reaction in the form of a 
>> growing
>> carbonised region.
>>
>> I've just had to cut a wide buried copper track in order to be able to
>> remove the carbonised pcb beneath it, which is disconcerting, but it will
>> just need soldering, or replacing with a piece of wire. I'm more worried
>> about what to use as a 'filling' in this cavity. I said I'd use epoxy 
>> resin,
>> but the usual stuff is damaged by soldering temperatures. I have some 
>> 'Auto
>> Weld' which says it's resistant to a constant 300C and should do. Once I
>> fill that hole back I'll never get it out again, so I'd better fix it
>> properly!
>> I'd like to add that I'm feeling pretty angry about those electrolytic
>> capacitors. They are sheer vandalism! Time for some companies heads to 
>> bow
>> down and appologise! Those unstable low dropout regulators are another
>> annoying self destruct mechanism too!!!
>>
>> Alan
>
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