Frost Drive spluttery, works only when i thouch it on the back of the pcb????

G

Grazza

Active member
I am troubleshooting this frost drive build and its confusing me. It has sound coming through but its weak and splutery (if thats a word). Then if I touch it with my finger on the back of the pcb in the area that I have pointed to in the photo it works as it should for 30 seconds or so. I think if i hold it for a little longer it works for maybe a minute or so then reverts to being splutery. Component values checked, is built in sherbert mode. Components also re-flowed. IC values are pretty out there, listed below, these are taken without me touching it, if I was fast maybe I could touch it and then see if they change.

IC 1 1-8
25mV, 25mV, 22mV, -8.21V, 1mV, 2mV, 1mV, 8.48V
IC 2 1-8
-24mV, 1mV, 0mV, -8V, 0, -23mV, -23mV, 8.4V
Charge pump 1-8
8.5V, 4.8V, 0V, 3.4V, -2mV, 3.6V, 5.1V, 8.5V

Does this suggest a power issue? I don't really know where to go from here with it, still a novice at troubleshooting. 95% of my builds just work straight away. I have also tried swapping out IC's etc and no change.
 
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Your charge pump is your first problem. Pins 1 and 8 should be around 9V which you mention above. Pin 5 should be -9V or close to it. Where did you get your charge pump? Could be a fake or got damaged.

1752785628822.png
 
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I have tried swapping out the charge pump, I think I have more I'll try again, those voltages were way out. Charge pumps from tayda.

I'm not with it now but is c7 the mlcc? From memory I put it in for space, it's a 220nf from memory, tested it before it when in and it was exactly to spec. Code 224 I think from memory.
 
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I'm not a savvy trouble-shooter, but...

The area you pointed to is C3, C5, C11 and/or R16, R3, R4, R5...

The fact that you touch it and it works makes me think it's a grounding issue.
Grounding or it's a cold solder joint or damaged trace that makes a connection when pressure is applied;
That it works for a short time makes me think when touching it a cap is then able to fill-up/drain, you stop touching it and the cap no longer is able to drain/fill-up whatever — that's why it eventually reverts to being sputtery once you stop touching it.

C3 is just in the loop of the op-amp, you could remove it and get a brighter signal is all.
C5 is a coupler so if it's faulty then signal isn't going to get through, Full Stop.
C11 is part of a filter at the output of the circuit working in conjunction with C10 22µ. May be something to do with it?


If it's not grounding properly, then it needn't necessarily be just the components you were touching (C3, C5, C11), 'cause the charge-pump problems somehow play into all this — a grounding failure could manifest itself in a separate part of the circuit.


Like I said, I'm not a technical-savant and more experienced capable people must be having a chuckle over my armchair diagnostics.

Nonetheless, I'd be checking the values of caps and solder joints with anything related to the charge pump. Maybe there's a solder-bridge under the socket. Does the charge-pump run hot? Has the only testing you've done occured outside the enclosure?

If I wasn't stabbing in the dark before, I certainly am now.
 
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Great post, I have re-flowed that area and I replaced a couple of film caps there, but will re-flow again and investigate further. Don't know if the charge pump runs Hot but will check. All it takes is the slightest touch to get it going. Will also try to check for solder bridges at the socket too.
 
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I don't know why I never noticed it before, but you've got the flyleaf type of socket for the charge pump.

I'd pop out the chip and inspect that socket closely, very closely...

Some people get on OK with those sockets.
I've never had much luck with them, and when somebody convinced me to give them a second chance and this happened:

704238a6-ebde-4e30-96a4-18ed8e94cd04-jpeg.25753



I prefer machined-pin sockets.
 
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Yes, I hate those sockets, I tried them on this batch of PCBs and I regret it! I'll never buy them again, I've had similar problems. I was being a tight ass. I've since bought the good ones but I thought I'd use them up.

Will check there is nothing wrong with the socket.
 
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The -9V pin on the charge pump is not measuring -9V. That -9v connects directly to the power pins on the op amps, and you measured -9V on both of those (or close enough). That does suggest to me that the charge pump can deliver -9v, but doesn't always. I would definitely be looking at the socket and the soldering around the charge pump section. It almost seems like the chip is good, but there is a dodgy connection there somewhere.
 
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Ok, inspected the socket, it appears ok but I can't see inbetween it and the PCB obviously so I'm not sure if anything is truly wrong. I reflowed the area again, changed out the charge pump chip and gave it a good look over again for the millionth time. It is still the same. I did poke around (literally with my finger) at it, and the pedal only works when I touch the two pins of C3. Has to be both pins though it is hard to just touch one pin accurately with my fat finger. but when I touch it, and only has to be lightly, it ramps up like its filling up with charge, and then the pedal sounds great, which is disappointing. If I hold my finger there it continues to work, but playing guitar one handed is a bit shit. I'm a little puzzled as I can't see the relation of c3 to the charge pump other than location.

Should I go ahead and try to pull the charge pump socket out and redo?
 
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