Smoking DEFX Laika Fuzz v2

[duck_arse]

Is it possible my Q6 (& Q7) BS170 mosfets have been DSG pinout all along (I inserted them assuming DGS?)

why? why assume? this is the modern world, the age of the information superhighway. is it not? look them up, both parts, 2N7000 and BS250. get the datasheets. check the pinouts. that's what manufacturers write them for.

one effect of backwards-ing yer mosfet would be that the led [assuming correctly oriented] would not turn off.

[Itchy Scratcherson]

I'm sublimating my ego in my embarrassment that it's taking so long to troubleshoot. I appreciate your help so much. ...and especially in the long run, thanks sincerely for teaching me how to fish for myself.
Yep. I've checked the data sheets and yesterday found that Onsemi has some BS170's pinned differently, so I tested my remaining 7 of those... as well as the 2N7000's stock I've got. In the world of possibilities maybe my whole batch of BS170's is actually bogus, but following the YouTube's instructions I do get 170's gate to open and close. Also, the telltale sign they ARE in fact correctly installed is: with MM set to diode mode, I get a reading only when connecting the outer lugs (S & D). Gate's in the middle just as the pcb's labelled.

Still can't get past the led problem. I've checked, replaced, checked, checked and double-checked that every component in the mil bypass is wired soundly and correctly, that the LED is still good. And now I'm confident that this voltage is supposed to go to ground when the mosfet opens, and that stays in such-and-such a range right now b/c it's fed by VRef over there, etc. Everything seems copacetic against the schematic... Throwing the bypass ON shows me 0.25ish-0.45ishV on the anode side of D1 4148 (this mil bypass 4148 leaks 0V when effect is off). You wrote that getting the mosfet gate to open is the only thing we care about, yes, (thanks for narrowing down the basic focus here!), but the mil bypass works on these minor voltages leaked by that diode, and I'm meticulously metering every point to see the effect of throwing the bypass switch. In other words, turning the circuit ON shows a proper change from the diode's anode but the !#@$# gate still won't open. I temporarily pulled the 3904 today b/c Mr. Keene states it's not necessary. The LED voltages don't drop to 2.1V+ 0.0- unless I manually bridge the Q6 mosfet's gate to drain,... I do that and voila! We have light!

So, short of that (a pun!), the bypass LED's not lighting... unless I bridge Q6's gate and drain... then the LED voltages go to 2.1V A+ 0.0V K-; doing so also causes Q7's gate to open. BUT, at Q8 the SK30A-Y won't let anything through, regardless of the 3PDT Drift state.

Is it a bad idea to just implement my workaround: my bypass toggle is currently a DPDT b/c that's all that's needed to connect the relevant pins to turn the PCB on. It's wired exactly as the v1 Laika wiring diagram, just without the middle vertical column that's not doing anything anyway. If I use a 3PDT I can mechanically bridge the mosfet gate -to-drain when engaged, and free it up when bypassed. I don't see the harm. Except of course, leaving the prime issue hanging.  :|

[duck_arse]

all BS170 and all BS250 will have the same pinout [but different internal polarity - DO NOT interchange].

all 2N7000 will have the same pinout. further - ALL 2N7000 are 180^o opposite pinout to all BS170.

2N7000 and BS170 are equivalent - NOT identical [due to pinouts]. as it happens, I've never had my hands on the BS parts, so they confuse easily for me, the 170 and 250.

match your BS170 to the silk-screened layout - don't guess. don't try the other way. your 2N7000, on the other hand, when substituting 2N7000 in for the BS170 [ -NOT the BS250- ] fit reverse to the silkscreen.

FORGET about measuring the gate voltage - each time you do will affect what the mosfet is doing. here is a test to clear the gate connection of the mosfet.

POWER OFF. leave it off when measuring resistance.
meter to ohms range.
connect one probe to the wiper of the SIGNAL pot [which is a volume control].
connect the other probe to the gate pin of the Q6.
what reading on the meter?
now work the BYPASS switch once. now, what reading on the meter?
work the BYPASS again, once, and now what reading on the meter?
move the first meter probe to the SIGNAL pot pin "3" and R21 junction. this will now measure the pot wiper-gate resistance. what reading? vary the signal pot, does the reading change?
work the bypass switch, what reading? vary the signal pot, what reading?

[Itchy Scratcherson]

«post deleted by OP»

[Itchy Scratcherson]

Couldn't keep away!
All metering was done with no power connected. Q6 is a 2n7000, correctly installed...

POWER OFF. leave it off when measuring resistance.
meter to ohms range.
connect one probe to the wiper of the SIGNAL pot [which is a volume control].
connect the other probe to the gate pin of the Q6.
what reading on the meter?
(1.) bypassed; Signal pin2 -to- Q6 gate: 3.84kΩ

now work the BYPASS switch once. now, what reading on the meter?
(2.) engaged; Signal pin2 -to- Q6 gate: 801kΩ

work the BYPASS again, once, and now what reading on the meter?
(3.) bypassed; Signal pin2 -to- Q6 gate: 3.84kΩ (as before)

move the first meter probe to the SIGNAL pot pin "3" and R21 junction. this will now measure the pot wiper-gate resistance. what reading? vary the signal pot, does the reading change?
(4.) bypassed; junction of Signal pin3 & R21 -to- Q6 gate: 98kΩ, 110.6kΩ, 58kΩ, etc. (values change as pot setting changes)

work the bypass switch, what reading? vary the signal pot, what reading?
(5.) engaged; junction of Signal pin3 & R21 -to- Q6 gate: 5.85MΩ, 9.2MΩ, 9.7MΩ, 950kΩ (values change as pot setting changes)

[duck_arse]

alright. now, let's assume, just for the moment and at our peril, that your diode-to-gate is good and correct. and that the led is wired with clr to supply correctly. and that the parts themselves are good and working. your measures suggest that the mill itself should function correctly.

what does the led do when you work the bypass at the current state of play?

and, this, a few observations from your first posted photos [because you haven't paosted any updates].



see that bent-over tab of the transformer? please measure the resistance between that tab and the trace from the Q8 pin it is draped across. if there is a short there, it will crimp your copacetics somewhat.

and now, back to datasheets for you, I'm afraid. seek the datasheet for the 2SK30A jfet, and it will show a centre gate pin. the source and drain are [ARE] interchangable in this part, so the K30A can go either facing. remember I asked about the J201 [the through=hole part part number] as a replacement? and it needed twisted legs to match the board footprint?

well. your surface mounted part would be the MMBFJ201, wouldn't it? and when you seek and view that datasheet, you'll see it also has a centre gate pin. and you will see the note about drain and source. but when I gaze upon your photos [unless you have done changes and not updated the pics] I see that the legs on from your adaptor ARE twisted. mind, this is just what I can see from what you have shown, and may be completely wrong. but now it's to you to look at the datasheets and the adaptor board and the circuit board overlay and work out what pins are going where, and then maybe correcting them.

straws - clutched. good luck.

[Itchy Scratcherson]

Will do! fwiw, the tiny green transistor adapter I'm using is quite generic, and I adapt to it, following only which trace goes to which pad.

[Itchy Scratcherson]

I used to be very pretty. Haven't butchered a pcb this much since a year ago when I finally got kester solder, some extra flux, and gradually improved my touch & timing.

Resistance between the transformer's top tab to the trace it's smooching is 1.7Mohm. Of course, you've seen I bridged the bottom tab to ground so it conforms to the Laika (version 2) schematic.

Would you kindly help me understand the importance of measuring resistance in a case like this... I was about to reply with just "there's no continuity"... then I remembered that's not what you asked for. 

[Itchy Scratcherson]

Do you think we should call it a wrap & I'll just replace the board? fwiw, the pcb passes sound and responds to both filters, 3 out of 4 pots (no scan functionality), and the diode reverse has no audible effect. No Led in bypass or engaged state; the drift led does function correctly. I've pulled the LED & it lights with a 3V button-style battery. Voltage to the Q3 Ge transistor collector is low (~3 or 4V tops).
Thank you for all your time & attention.

[duck_arse]

Will do! fwiw, the tiny green transistor adapter I'm using is quite generic, and I adapt to it, following only which trace goes to which pad.

generic, until you solder something to it, at which point those 1 2 3's become specific.

argh. I seem to have confused Q1 and Q8. what part have you on that daughterboard? apologies. most of what I typed above is wrong.

anyway, observe the circuit diagram, with Q8 - one leg goes somewhere, the other leg goes somwhere, but neither go to ground. if the transformer frame tab then cuts thru the mask and shorts the fet pin to ground, that will cause unintended problems.

continuity says 'yes, beep, there is a connection' whereas resistance says an actual figure, high, low, in between. use contiuity for open/not open checks.

looking your new pics, I wonder why you took the sockets out. and, yes, I'm afraid I'd suggest a new build and board.

[Itchy Scratcherson]

looking your new pics, I wonder why you took the sockets out.

seemed at the time I was almost there, so I went out on a limb (which I thought'd be so simple to climb down from)

and, yes, I'm afraid I'd suggest a new build and board.

let's go with this sage suggestion, and when I rebuild it and it works the first time, we'll celebrate
Thank You for your invaluable and generous assistance, duck_arse!

[Itchy Scratcherson]

I've worked professionally for a number of years in technical support over the telephone and in field support in NYC for a well-known software/ hardware company in the film & tv industry, helping beginners, experts, and everyone in-between. That's just to say that I hold an appreciation for your patient, sustained help!
When I wrote about "assuming" pinouts, I was pretty tired and exasperated. I do have a special transistor meter, and from nearly the beginning of my diy-pedaling, I've always checked the data sheets before installing. That said, I appreciate your strong emphasis regarding pinouts, and admit I sometimes do need to be told some things twice/ fall off the bicycle more than once in order to learn. I can't express strongly enough the gratitude I feel for your generosity, duck_arse. After 125 different circuits, I really was stumped on this one. My first post here has been especially valuable because you've stuck with me. Thanks again! Christopher

[Itchy Scratcherson]

So, wrapping it up, I understand what continuity is, and I understand what resistance measurement is, but I was surprised when you asked me to check the resistance of a xformer tab against a particular trace on the board, because I would have merely checked for continuity. Black or white. Asking for the resistance measurement made me think again that perhaps lack of continuity is not definitive in terms of whether there's an unwanted connection or problem. Could you please clarify? Thank you.

[duck_arse]

thank you for your comments, though I don't really think I deserve the compliments. and sorry for getting so confused and misleading in the kuwait and q1 business.

frankly, the continuity buzzer on my dmm always pessed me off, so much so that I cut it out of the meter. so my usual reach-for is resistance, not continuity. and continuity buzzes, buzzes, buzzes up to some value of resistance, then does't buzz, wheras that level of resistance may well be a problem in circuit. the mill gate, fer inst - resistance up to megohms will still pull the gate to off, but continuity measure buzzer would have given up in the hundreds of ohms.


we don't get much mention of copacetics around here.