please help me cure my hot tubes

[smccusker]

Hey everyone,
I have a 70s EH Hot tubes (the solid state one), which i love to death, but which has recently started making loads of noise. The noise gets worse as I crank the overdrive, which makes me think that the cause of the problem is before the overdrive pot. the overdrive is otherwise weak and there is hardly any sustain. I'm thinking maybe the 470u capacitor in the neg feedback loop is crook, is this a likely problem? I will post some voltages and things when i get home later tonight, but for now there is a schematic here.

[smccusker]

hi again,
I checked some voltages and audio probed around the circuit a bit, here's what i found:

IC1
PIN 1 = 1.58v
PIN 2 = 1.58V
PIN 3 = 1.66V
PIN 4 = 0.0V
PIN 5 = 1.58V
PIN 6 = 1.58V
PIN 7 = 1.58V
PIN 8 = 8.92V

IC2
PIN 1 = 0.0V
PIN 2 = 3.67V
PIN 3 = 3.66V
PIN 4 = 0.0V
PIN 5 = 3.69V
PIN 6 = 3.64V
PIN 7 = 3.93V
PIN 8 = 3.63V
PIN 9 = 0.0V
PIN 10 = 8.92V
PIN 11 = 0.02 (?)
PIN 12 = 8.92V
PIN 13 = 0.03 (?)
PIN 14 = 3.71V
PIN 15 = 3.73V
PIN 16 = 8.92V

when i probed around the circuit, i found that there was a slight ammount of noise present on the tip of the input jack when the circuit was engaged, but not when bypassed (I modded this pedal for true bypass a year or more ago). Pin3 of IC1 was clean with the same ammount of noise as on the input jack. Pins 1 and 2 of IC1 had "crackly" distortion with not much sustain. Pin 7 was the same but louder. pins 5 and 6 were dead silent.

Im not sure what to make of this, given my noobishness, but i think that the problem might actually be IC1?
Any thoughts or suggestions would be greatly appreciated, because this is my favorite pedal and my rig just doesnt sound the same without it.

[smccusker]

pretty please???
<bump>

[smccusker]

woah tough crowd...

is there any more information that i could post that would be helpful? I dont mean to pester and keep bumping my own thread, but it would be really great to get some ideas, even just on where to focus my search for the component(s) in question.

[runmikeyrun]

check your connections... i just had a big muff doing that same thing, except intermittently.  I could get it to do it when wiggling wires going to the board so i thought it was a wire, then i noticed it did it when i flexed the board.  When i got in there with a light up magnifying glass i found a lead from a transistor emitter that wasn't making a good connection with ground.  A touch of the iron and it was back on track.

good luck!

[smccusker]

thanks for replying runmikeyrun.
Ive been over and over the board with a magnifying glass, and havent really been able to find anything that looks suspect. I gently wiggled all the caps on the board to see if that made any change in the noise, but it didnt. I swapped out a 1uf cap that looked leaky. I thought the overdrive pot might have gone funny, so i disconnected it, measured it and put it back in when i couldnt find anything wrong with it. something HAS changed though. The noise seems somewhat reduced now, but the distortion still doesn't sustain well, and kind of fizzes out. the overdrive pot now seems to have no effect on the signal, or the noise, but i shorted it out of the circuit and the noise in the signal suddenly became extremely loud (sounding more like what it did before i started desoldering, and when the overdrive pot was at max). I tried to get some voltage readings for the pot, but the meter was jumping around all over the place. lugs 1&2 would sometimes start at 2.7v and then drop logarithmically down to 0 (like a cap discharging), and sometimes it would drop to about 1v and then rise back to above two and then rise or fall between those two with no clear pattern. I tried to get readings maybe 5 times and never got the same results twice. lug 3 always read 3.616v.

I'm not sure what all of this means, i think i'm even less sure of the cause now than when i started. any thoughts or suggestions would be an enormous help, because i'm well out of my depth now.
thanks!

[Mark Hammer]

Two things to consider:

1) The 4049 chip it relies on is dirt cheap and widely available.  You can just stick in a new one.

2) The HT is of an age where some of the electrolytic caps on board may have past their best-before date.  They are also cheap to replace.

Just to let you know, the HT will run off a 9v battery.  Not for a VERY long time, but certainly long enough.

[smccusker]

thanks for replying mark.
I will bite the bullet and replace the electros and ics as per your suggestion and pray to jeebus that i dont lift any of the traces when desoldering 

i actually like that the ht runs from mains power, its one less pedal have to worry about dying batteries before and during a gig! (although i'm FINALLY getting around to building a regulated supply/distribution box this weekend, so i guess that wont be an issue anymore anyhow.)

thanks again!

[smccusker]

well after some drama with traces lifting, i socketed a new 4049 into the board, but now it just oscillates like crazy. Im definitely sure that its oriented correctly and i'm definitely sure that all the pins that are supposed to be held high are getting the 9v. CMOS are static sensitive right? would smoking the chip be a cause for crazy oscilation?

[Mark Hammer]

They ARE static sensitive, but they won't fry just by looking at them cross-eyed.  They're hardier than that.  As much of a recommended practice as it is to socket CMOS ICs to avoid static discharge damage, it can be the case that a "new" chip comes into your possession with somewhat tarnished pins which might fail to make contact with a budget-conscious socket.  Consider replacing the socket using one with machined pins (instead of the cheaper spring-leaf type), and consider scraping the sides of the IC pins just a bit with a utility knife so that they are nice and shiny and make good contact.  It CAN happen that one of those unused pins you need to tie to V+ is sitting there not making contact without your knowledge.

[smccusker]

I am actually using one of the machined sockets (which i always find much harder to get those damn ics into), but im pretty sure contact isnt the issue because i took the voltage readings from the legs of the actual IC, not from the pins on the underside of the board. i'm heading out to the store this afternoon to get some bits for another project, so i might just pick up another 4049 chip while im there and see if that behaves any differently.