May 3, 2020 at 1:49 pm #12728
Having some issues with Mastadon build. I am getting a signal but it is very faint..maybe 1/4 of unity but hard to say. While quiet, I can tell that the controls seem to be working as intended. Below are the transistor measurements. The only thing that seems bad is Q2 Collector. I reviewed a previous trouble shooting thread and confirmed continuity based on the suggestions in that post. I have double checked components (I also use DMM to check before I install each one). The only components substitution I had to make was R3 which I used a resistor that measured 48k because I had no 51k. I tried several different 3904’s and tested all on DCA55 prior to installing.
Q1-E = 0.0 Q1-B = .58 Q1-C = 1.46
Q2-E = .86 Q2-B = 1.46 Q2-C = .98
Solder joints all look good…and continuity tested between pots 3 / 4 as well as continuity to output, ground on those pots, etc.. Some solder joints are hard to see because of board mounted pots…also hard to reflow if I wanted to. I am running it through a test rig that I know works…just connecting power, ground, in and out.
Before I tear this thing down and remove the pots, etc. just wanted to see if anyone had any suggestions what else I could check. I only have very rudimentary understanding of electronics. I did take another couple measurements. Going into R3 I get 9.45v (same as battery) and on the other side I get the .98v…same with C4 and C5 and same as Q2 Collector. Not sure if this matters…again, not a lot of understanding on my part.
Anyway, just hoping to avoid tearing this thing down and starting over. Kinda bummed…this is the first one of your PCB’s that didn’t fire right up and work perfectly. Hope I can figure out what I screwed up…
Thanks.May 3, 2020 at 6:22 pm #12732BarryKeymaster
Pics.May 3, 2020 at 6:28 pm #12733
So decided to quit stressing about the Mastodon and build another pedal…hooked it up to the test rig…SAME PROBLEM. So, pulled out another test rig and it fired right up. Plugged the Mastodon into that and it fired right up too. I would say it was time to trouble shoot that test rig…except that it met with a sudden impact against the concrete and then got zombie stomped.
So…the Mastodon is working…but, now just wondering…what about that “off value” at Collector of Q2? The guide says 2.3 and I measured nowhere near that. I measured it while hooked to the test rig as well as just to a battery. I just compared to one that I built on vero and they sound very similar…
Thanks for any thoughts on this…May 4, 2020 at 4:53 am #12736CybercowModerator
A lot of emphasis (or often times a lack of emphasis) is placed on the word “guides”. The guides, as well as electronics, need not be EXACTing. If a guide says 2.3v at a specific point, but the measurement is way off, but it still sounds as anticipated, hoped or good, then the EXACT measurement is not as important as the end result. Electronics is a fickle mistress and she can be devilishly playful. So, if it sounds like another you’ve built and\or works as expected, a pinpoint voltage measurement at a specific point is not really required. What matters is that it works.May 4, 2020 at 10:52 am #12738
Thanks! Now I just need to update the subject of the thread to “Mastodon Build (No Problem to Resolve)”.
It really wasn’t my weekend. I re-measured and I am guessing I had one of the pots cranked all the way down which, based on my limited understanding, would impact the collector of Q2. I re-tested and was getting about 2.8v.
I think I was just flustered that it didn’t fire up first try. I have had such excellent results with these kits…well written guides, quality PCB’s, good mod ideas, etc. Once I developed my process for building effects, based on some failed vero builds, I have been super lucky and had stood at 100% through a dozen or so of the guitarPCB boards. I still get some failures on my vero builds because it seems that no matter how many times I double check cuts and links occasionally mistakes will be made.
Sorry for “crying wolf” on this one.May 4, 2020 at 12:39 pm #12739wilkie1Moderator
Your “wolf Cry” is important! It shows others on the forum another example of what kind of errors can be encountered when building.pedals. That’s important to share.May 4, 2020 at 2:25 pm #12741mybudParticipant
‘Electronics is a fickle mistress and she can be devilishly playful.’ Well put, Cybercow.
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