SB4000 Support Thread

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JMan

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Calibration procedure will answer questions about PRE-trim values... :eek:  ???  Well I have indeed read through the calibration steps and there’s absolutely no mention of PRE-trim values, because... I mean, by the time you’re doing calibration, you’re no longer at the “pre” stage, ya know?  ;D

Okay then, I’ll take this to mean that the pre-trim values I have taken from the schematic are the only ones I need to worry about (plus the ones in the power supply section that must be set to 1k33), and the others are only adjusted after they are in place on the board during calibration.

I’m still a little confused on why VR16 is a 50k pot that the schematic says to pre-trim to only 6k.  Seems a bit weird to me, but what do I know...
 

Chrome Heart

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"Okay then, I’ll take this to mean that the pre-trim values I have taken from the schematic are the only ones I need to worry about "
Give that man a cigar.
 

JMan

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I’ve reached the point where I’m ready to wire up the transformer.  I’ve drawn out a picture (attached, sorry that it seems to be uploading sideways).  Does this all look right?  I feel confident about the grounding and the secondaries, I think, but I’ve seen conflicting info on the primaries and where they go, including one person saying it doesn’t matter which pair of primary wires goes to L and which goes to N. 

I don’t yet have the expertise to sort out what of that info is correct or relevant to me at this point, so I’m hoping you all can help.

I’m using the Triad VPT36-690 toroidal.  The IEC is the fused Schurter 6200 from the BOM.
 

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Rob Flinn

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This looks like it's covered in the build manual that is in the first post of this thread.  Look at the completed build picture.  It shows how the secondary of the transformer is connected to the psu board.  For the primary you picture looks ok if you are in a 115v area.
If you rwad the build manual he suggests having the main board disconnected & testing that you have the right volts in the right place.  This is good advice.      His instructions are pretty clear really .....
 

JMan

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Hey Rob, thanks for the reply.  Yes, I have a printed out copy of the build guide on my bench, and the secondary wiring in my picture came from there.  I definitely plan to follow the guide when it comes to power-up and voltage testing, and yes, I’ve read through that very carefully.  Truly, I am just trying to get input from you more experienced folks here (I am a noob) regarding the primary wiring.  I did forget to mention that I’m in the USA and wiring for 120vac, as you noticed. 

So anyway, you’d say that part looks right?  I’ve had some comments elsewhere about the switch I’m using, folks saying it should be a two-pole instead of three...  Do you think there’s merit to that, or will I be fine as is?  Again, I’m fairly inexperienced, so I’m just trying to get clear answers from those who know more so that I don’t hurt myself or the equipment.
 

Rob Flinn

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JMan said:
So anyway, you’d say that part looks right?  I’ve had some comments elsewhere about the switch I’m using, folks saying it should be a two-pole instead of three...  Do you think there’s merit to that, or will I be fine as is?  Again, I’m fairly inexperienced, so I’m just trying to get clear answers from those who know more so that I don’t hurt myself or the equipment.

The switch you are using is a 1 pole 2 way/throw switch.  It is better to use a 2 pole switch because that way you switch off both sides of the mains.  I think in some countries that is a legal requirement.    If your switch has 2 throws it is safest to wire it so the incoming mains is connected to the 1 of the throws & the mains is taken to your PSU Pcb from the pole.  The reason being if you have the mains coming in on the pole, then when you switch the unit off you will be switching the mains to the unused throw & it will be live.
 

JMan

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Rob, thanks for that explanation!  That actually helps a lot.  I think I’m just going to grab a 2-pole switch, as it sounds like the safest option, and it’s a very inexpensive improvement.  In that case, I’ll look at the data sheet for the new switch, but I’m guessing there’s a right and wrong orientation for the primary wires going in/out of the switch...? 
 

Rob Flinn

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JMan said:
Rob, thanks for that explanation!  That actually helps a lot.  I think I’m just going to grab a 2-pole switch, as it sounds like the safest option, and it’s a very inexpensive improvement.  In that case, I’ll look at the data sheet for the new switch, but I’m guessing there’s a right and wrong orientation for the primary wires going in/out of the switch...?

As I said in the previous post if the switch you happen to get has 2 throws or ways.    i.e the pole can switch to 2 sets of contacts the best way is to wire the primary of the transformer to the poles, & the incoming mains to one of the throws.  This way you don't have a pair of live throws when you have the unit switched off.
 

JMan

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Rob, I mocked up another picture here (I am a visual learner).  I’m trying to understand your explanation — which again, thank you, I am just still struggling to synthesize all of the new information I’ve learned, as I have no background in electronics aside from a the passive stuff inside electric guitars.

If I understood you correctly, and went with a dpst switch, is my drawing basically what you meant to convey?  (If not, I’ll delete so it doesn’t confuse anyone else).  I’ve only drawn up the primaries, so please ignore the absence of a ground.
 

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JMan

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Well darn, guys!  I powered my unit up for the first time tonight, and everything was fine for a minute or two, then suddenly got a puff of magic smoke from the psu — looked to come from around the area of R182/183 and D29/30.  I haven’t done much investigating yet, although I have done a visual check to make sure my diodes and other polarized components are all oriented correctly (since I bet that’s one of the first things I’ll be asked).

I was also getting some off voltages for the few moments that I was taking them prior to the smoke.  But part of me wonders if I wasn’t probing correctly...

Anyway, that’s just an update.  If anyone has immediate thoughts, I’m happy to get the input.  Otherwise, I’ll revisit it this weekend and see if I can suss out the issue.
 

JMan

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Well, I did a bit of poking around with my DMM  on the power supply this afternoon (power turned off).  The resistors *seem* to be fine, and none of my caps are bulging, but I’m getting different readings on a couple of my diodes.  D26 & D28 are reading ~0.12vdc on my diode checker setting, while the rest of the diodes on the psu board are reading between ~0.55 (+/- a couple hundredths). 

So my question is, which of those seems right and which seems wrong (since they’re all 1n4002)?  Google/data sheet haven’t yielded the answer, at least with my search entries, so hopefully you guys know.

It’s easy enough to replace the diodes.  Is there something else upstream in the circuit that could have caused it?  (In other words, what other likely suspects should I triple check?)  I’d hate to replace components only to have the new ones immediately blow as well because I didn’t catch a different error.
 

Rob Flinn

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I would deinitely replace the diodes you have that measure 0.12v.  1N400x are silicon & should be 0.6-0.7v, however, 0.55v could be acceptable.  Maybe you could measure one of your spares to see what you get off a new one to evaluate the others.   
 

JMan

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Thanks, Rob!  And great idea to measure against a spare, I’ll do that.  Got nothing but time right now thanks to the pandemic, so I’m actually looking forward to a bit of fiddling on this thing!
 

JMan

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I did test a spare 1n4002, and it’s reading right at 0.6vdc.  Since all the ones on my board (excl. the ones that are clearly blown) are measuring in the low- to mid- 0.5_ range, I’m wondering again if there might be something upstream that weakened them (is that a thing?) when I powered up the unit.  It wasn’t on for more than a minute or so.  Or do you suppose I’m creating worry where there isn’t any?
 

Rob Flinn

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WHat I would do is replace  the two obvious blown diodes, but check all the circuitry that relates to them.  Check if there is a short in this part of the circuit when the diodes are out.
 

felix1988

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Hi Guys,
any chance someone could post a BOM or Mousercart and the build manual? all the links I found are dead unfortunately.
Thank you!



EDIT:  I found a BOM by the member "daal", attached it here for future reference.
 

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JMan

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Did you find the build manual? I’ve probably got a digital copy knocking around somewhere if you still need it.
 
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