Hi all, in the interest of saving what hair I haven't yet pulled out I am after some sage advice, a friend gave me a RAT2 that he had inserted a IC socket and an LM308 chip, the sound was very fuzzy and thin with no sustain, a bit like an asthmatic wasp in a jar, I checked it over and all appeared to be okay, so thought I would replace most components mirroring what is in my 1980's Rat, after expense and time it sounded the same, so took them out again and gone back to as stock as I can remember, all the values appear okay, checking against schematics on line and I think the voltages on the LM308 are okay? but its still the same, I have added some pics and a drawing showing the values ( probably a four year old could have made it look better!).
Any help or advise would be gratefully appreciated.... ta
(https://i.postimg.cc/8Jf2xbtc/2021-02-11-17-34-IMG-1822.jpg) (https://postimg.cc/8Jf2xbtc)
(https://i.postimg.cc/vcsJSf98/2021-02-11-17-34-IMG-1823.jpg) (https://postimg.cc/vcsJSf98)
(https://i.postimg.cc/q689vvfd/2021-02-11-17-41-IMG-1826.jpg) (https://postimg.cc/q689vvfd)
(https://i.postimg.cc/kDKrcf2h/2021-02-11-17-41-IMG-1828.jpg) (https://postimg.cc/kDKrcf2h)
welcome to the forum,
are you suing a correct 9v supply, since there is 13V on pin one and 14v on pin 7??? that seems very off to begin with.
some solder points look like cold joints, you should reflow the ones that are dull/white and not shiny, and then clean of the board with a little isopropyl (cleaning alcohol/spiritus work as well) and an old toothbrush, since it looks really cruddy. we can help you better when its clean because we can see it better.
cheers, Iain
When you restored "back to stock", did you re-use the original components or install new ones?
Guys, thanks for getting back, I'll give it a bit of a clean, I think its mainly flux, i believe continuity is fine though, I have been through it with a probe and distortion is fine leaving the chip, it changes on the output filter side, also weirdly if you turn the distortion down the signal goes completely which isnt correct, when I put it back I did use mainly new components, only keeping some that I had changed out as I went and it still being faulty.. :)
What are the voltages on the JFET? Your comment suggests the biasing is off. Try changing your R10 to 2.2M and adding a 2.2M between drain and gate.
and - "." is not an allowable voltage measure. please post 0.00V if that is what the meter reads, sometimes the little number indicates grounding problems. [pin 5 can be wobbly volts, we allow a no read here.]
if you remove the IC from the socket and remeasure the voltages on the empty socket pins, do any of them change?
and g'day.
Hopefully this picture is a little better
(https://i.postimg.cc/McqrSnZB/0-BDD82-CA-E9-E8-448-F-AC55-D525-A26-A0130.jpg) (https://postimg.cc/McqrSnZB)
(https://i.postimg.cc/CRj6XG0Y/EDD53-F01-2-EBE-482-C-B169-8-E34503-FB61-B.jpg) (https://postimg.cc/CRj6XG0Y)
Thanks for the reply, change R10 as suggested and also added the resistor, unfortunately it didn't work at all after, with the switch engaged just get a low level hum/squeal...restored now, and back to original problem, obviously the loss of signal when the distortion knob is turned down isn't correct does that problem point towards something specific?..
it might be bias related, i suggest you lookt at this link:debugging guide (https://www.diystompboxes.com/smfforum/index.php?topic=29816.0)
cheers, Iain
Once again - what are the voltages on the JFET?