Nope, haven't heard from Paul yet. ∗hint∗ ∗hint∗
:)
I've done the hold-up-to-the-light trick, actually - looks fine - and
I've checked the obvious stuff like cables going to the right places
and resistors and ICs in the right place.
My hunch is that it's an IC leg short. From a look at the schematic, I
would think U3B, U5B or U4A... but I'm hesitant to just start redoing
the joints without knowing a bit more. The resistors in the LP section
look fine to the eye, but it's possible the problem is there.
About ICs - am I right in thinking U3A would be the side of the IC with
the little circular "dimple" and U3B the other side?
Matthew
On 25-Feb-06, at 10:00 AM, Geoff wrote:
> On the off chance that paul hasn't helped you out already (he's darn
> good at this, helped me
> track down the problem I had with my MOTM-300, which was, of course, a
> bad solder joint
> ∗somewhere∗) I would suggest some basic things. Check all of your pots
> for proper wiring,
> check for shorts on IC legs, and check for missed solder joints. Yank
> the board out of the
> frame and hold it up against the light. If you see any light in places
> you shouldn't (really,
> probably nowhere except cable tie points, but I don't recall exactly)
> then you've got a problem.
> That's a ∗great∗ way to find missed vias and solder joints. Good luck!
>
> -Geoff
>
> Matthew Hiscock wrote:
>
>> Hi all,
>>
>> I just assembled a '420 and am getting a strange problem. I wonder if
>> anyone has any thoughts on where the problem might lie:
>>
>> In HP mode the filter works correctly - and sounds great - with no
>> resonance, but if I turn up the resonance, I just fade in more
>> unfiltered sound instead of increasing resonance. So that with the
>> resonance all the way open, there is effectively no filtering going
>> on.
>>
>> When I put it in LP mode I hear nothing from the inputs at all. If I
>> turn the resonance up I get a regular clicking. If I open up the res
>> the clicking slows down, and if I adjust the filter freq, I can hear
>> the filter acting on the clicking, but nothing from either of the 3
>> inputs is going through.
>>
>> NF is a weird mish-mash of both the above.
>>
>> After I first assembled it, it was doing this, then I double checked
>> some of the joints and via holes and it started working fine, then I
>> inserted a cable into the fm jacks and it went back to having the
>> above
>> problem. I've gone over all the stuff I did to get it working right
>> the
>> first time and no luck.
>>
>> I'm inclined to think that, because I had it working fine at one
>> point,
>> the problem is minor and that I'll find it in time - for example
>> something was jarred loose by inserting that cable - but I'm wondering
>> if anyone has any suggestions on places to start?
>>
>> Certainly nothing is loose to the touch, and everything seems to be in
>> the right place, but obviously I'm missing something, or it would be
>> working.
>>
>> Any help much appreciated,
>> Matthew
>>
>
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