Mac SE/30 making zipping and buzzing noises

[Tothwolf]

On Thu, 26 Mar 2015, dave at 661.org wrote:
> On Fri, 20 Mar 2015, drlegendre . wrote:
>> On Fri, Mar 20, 2015 at 6:03 PM, Chuck Guzis <cclist at sydex.com> wrote:
>>> On 03/20/2015 02:08 PM, David Griffith wrote:
>>>
>>>  Would that be the cause of a flicker in the crt?
>>> 
>>> To me, it sounds as if there's an arc going on in the FBT.  But that's 
>>> just from general knowledge--I have no experience with Mac SEs.
>>> 
>> It's been a while, but as I said, those power connections can cause all 
>> sorts of odd issues. Just carefully & completely re-flow them with some 
>> SN63 material (if you have it, else SN60 will do) and know that it's 
>> one issue you won't have to face.
>> 
>> IIRC, one unit with that problem had flicker, static in the speaker and 
>> also system instability. It was either an SE/30 or a Plus, I had 
>> several of each model at the time.
>
> Now for capacitor choice: would it be better to use surface-mount 
> tantalums or through-hole electrolytics surface-mounted?

IMO SMD type tantalums are just way too temperamental for these 
applications. They are very intolerant of ripple and can only safely be 
used at a maximum of half of their rated voltage (according to the product 
engineers at both Kemet and AVX).

I have some early 1990s equipment made up of 3 board stacks, and each of 
the boards in each device are absolutely loaded with tons of SMD tantalum 
capacitors. Each board has at least one SMD tantalum which is either 
browning or has failed catastrophically (thankfully the damage to the pc 
board substrate looks to be minimal). There is no particular pattern to 
the failures either, parts of different capacitance and voltages with 
different case sizes.

Rather than solid tantalum, Panasonic SP-Cap or similar aluminum polymer 
capacitors are another possibility. These are available in the same SMD 
case sizes as traditional solid tantalum parts. For that fact, you might 
even be able to find OS-CON parts with the same SMD footprint as the 
original SMD aluminum electrolytic parts, too.

For boards that originally used SMD aluminum electrolytic capacitors 
though, why not just use new SMD aluminum electrolytic parts? I've been 
doing this with good results in other equipment, including industrial 
control boards that need to last at least 10+ years in the field. Newer 
SMD aluminum electrolytic parts don't suffer from the problems the SMD 
electrolytics made in the early to mid 1990s had with faulty rubber seals 
(some of which was also due to the use of chlorinated cleaning chemicals 
during the manufacture of the boards).