'75 Small Stone 3094/dead stage question

[analog kid]

 Well I have a '75 Small Stone that I am trying to diagnose and bring back to life, this is the one with 6 x (EH4800's ) CA3094's four in phasing stages ,  and I figured there aren't many more popular crkts or more talked about on this forum so surely someone can give me a quick answer.  first , it's only passing a dry signal through the effect output and the color switch does have an affect but only on the overall volume level.  checking voltages of pin5 of each of the first four ic's there is fluctuation so the lfo seems to be working.    Further on, using the audio probe I found there's 'wobble' on the first two IC's pins 1/2  HOWEVER at the third IC there is NO Signal coming out of Pin 6!! and hence no signal at all continued to that last phasing stage.      so a couple of questions
   -- there is wobble at pin 1 of that 3rd IC(the .0068 cap path)  and audio at Pin 2  (the 27k r path from the previous stage) BUT NOT any wobble to it at pin     2  , like there is on the previous stage's IC.   
   --  Although there IS the phase wobble at Pin 1 going into that last good stage , there is a very low voltage here (.5v) compared to the previous two ICs' pin 1, which are at 3 and 4 v respectively.  Also , although there is No audio leaving this IC stage at pin 6 , there is a voltage fluctuating here.  HOWEVER rather than 3 - 3.2v fluct. at pin 6 of the previous ic's , It's only showing a 1.1-1.3v at pin 6 of this IC. 
  SO Is this indicating a problem with the connecting stage components or IC3 surrounding components   OR would these all be the case if the 3094 itself was bad?   i am trying to avoid any IC desoldering as of yet not to mention ordering a replacement since none in the bins!  I have reheated joints around this ic already. and I can't imagine any bad resistors...   there is a 10uf cap connected to pin 4 ground next to this ic , one of only two electrolytics , but I doubt that could be an issue.

   --- another piece of helpful info to determine if the 3094 is bad itself  , is that the Pin 5 lfo voltage is identical to that of the previous stages ICs

here's a link to the schem my unit uses (though I've found a couple very trivial differences
 
http://analogguru.an.funpic.de/pictures/EH_SmallStone_75_c.gif

thanks for any help on this

[StephenGiles]

It should be possible to desolder the 3094 carefully. Personally, I would desolder them all and use sockets. It would then be easy to find out which one is defective. I would test the power lines to IC3 as well.

[Gus]

I worked on an early small stone it  was years ago but it was just a broken wire (the unit had solid core wire) and a bunch of bad solder connections.  It was a non plate thur PCB IIRC and that type of PCB seems to have more problems with bad solder.

I don't even start to troobleshoot an old EH or old mutron after I checked to find out what is the problem.  I check all switches and wires for  resistance and connections, then check/redo the solder THEN if it still does not work  troubleshoot using meters and a scope.

[analog kid]

Thanks Stephen , I was trying to first avoid any desoldering since it's an early one I hoped not to have to but if I had any 3094's on hand I prob already would've pulled that 3rd one knowing me    And yes btw pin7/8 of all the IC's is fine with V+
  It does use the solid core wire and same early cheap pcb Gus noted
  glad you shared your experience gus, I did take that into account to some degree but maybe jumped the gun getting into the troubleshooting. I did make sure that the switches were functioning,  all wires intact and  routed where they should be then started checking that power was where it should and ground as well.  BUT i didn't actually do a complete reflow job.  Only around those areas that I decided "might" be where problems are existing.   also a couple of long traces etc.. have really got discolored and cruddy with the strip of foam for the battery which I tried to scape off and shine up. I don't think this substance could affect continuity though, which I checked for anyway but just don't like cruddy traces!
   any ideas or diagnosis on what that stage/ic is doing  voltage and signal-wise??
thanks guys

[analog kid]

OH btw , the 10uf I was describing ealier is between ground (all pin 4)  and Pin 3 of all the the phase stage Ic's.  It just looks a bit suspicious but i haven't pulled and tested it yet.
And also thinking ahead  or for the purpose of thought if nothing else , how unconventional would it be to replace a single bad 3094 with a 3080 and darlington for someone who didn't have one on hand?  no trace working involved ,right? or enough of a PIA to just go find a 3094!?    getting ahead though I realize.

[puretube]

re-flow everything!

[analog kid]

Gotcha Ton! will do

[Gus]

GUITAR EFFECTS FAQ at geofex has good stuff

[analog kid]

Yeah ok I reflowed all over.   I do however have a new or revised symptom description.  audio probing again now that it's day time and I can really get some high volume audio w/o fear of hearing " I HATE THAT DAMN SOUND!!!, STOP IT!!"  I have now found that the wet signal IS there at that 3rd IC stage (pin 1,2, and 6 all have the same signal as the previous stages AND it's getting through to the last IC stage (pins 1/2) the same , as I'd thought it wasn't before. It is just that it's at a severely reduced volume beginning at pin 2, 6,etc..of that 3rd IC. MEANING that signal coming into pin 1 thru .0068ufcap is at volume is should be.

so if the wet signal is at least wobbling the same as in the first two 3094's like it should , would that neccessarily mean that the IC(s) themselves should be working ok?

I'm gonna check closer the 27k between Pin 6 IC2 and Pin 2 IC3  and the other resistors off of pins 2 / 6 of this IC.    The problem HAS TO BE within here , or the 3094 itself.

[puretube]

I`d like to get more involved into this debugging (a.o., coz I got exactly that same old vintage toy, that I love, somewhere...*)
but: no chance within the next 2 weeks to get it on the bench & hook it up to the scope/amp,
and: I don`t have experience with broken 3094`s - i.e.: I can`t tell the symptoms...
(but I definitely gotta agree with all that Gus wrote, in general).

*: opened up, but in working condition...

[analog kid]

I appreciate the assistance and willingness to help Puretube, regardless.
  Well that's what I don't know about either and would love to find out (BEFORE I'd decide to $$ for one or two , IC3 and possibly 4, 3094's) is whether or not these are the symptoms and behavior I'd get  if the IC was actually bad.
To reitterate as I said , the wobble is still there at Pin 2/6  and leaving on to the IC4 stage all the way to the output (mix)  BUT the Gain is extremely dropped at this point!!
I also have also now pulled , tested and tried new resistors for each of the r's connected to pins 2/6 of 3094 IC3 to no avail.  including the 27k that's feeding the input of this stage.  It's strange to me THAT'S where the gain is reduced , coming in from the previous stage the signal is strong across the Cap to pin 1 but across the 27k to pin 2 it's reduced greatly.
remember also (anyone who's thinking) that the Pin 6 voltage here on IC3 is alot lower than the previous 3094's.   around 1v instead of the 3v or higher on IC1 and 2.   Not to mention the fact that Pin1 , although signal is strong here , is low around .5v rather than 3-4volts....  THIS stuff leads me to worry of the 3094 here blown.  l
    come on transconductance amp phaser heads!

[analog kid]

Well here's another update for ya!
  As I said I've been testing and replacing everying resistor around that third 3094 trying to figure it possibly it's a bad solder,resistor,etc.. even the cap from previous stage causing the prob in the 3rd IC stage.   (anything besides the IC itself I was/am hoping)
when it hit me for troubleshooting / diagnosing purposes to just disconnnect the  cap and resistor from stage 2 to 3 and connect a .0068 cap from out of second stage Jumped to Pin 1 of 4th stage , effectively eliminating the 3rd . And whatt ya know?   I've got phasing at the output! suttle 'bout like a 45.  I just realized though,  I didn't connect  a  27k resistor from output of stage 2  to the  IC4 pin 2.   Oops, well it still worked w/o it. 
(don't know what all this tells me but at least to determine that the 4th one is good I guess)  But based on this and all else IF YOU GUYS WERE ME, Would you just pony up and order up a 3094 then?   I was wondering about those other two 3094's NOT in the phase stages. I don't know how they work but what the chance this IC3 isn't all dead and if the unit would function if this one was swapped for one of those positions.  I know kind of a dumb way to think.  probably a better idea to figure how to work a 3080 in ic3 position.  that musn't be as easy as I'd think though.

  I can imagine what it sounds like w/ stages all working , since it's almost useable like this     did I mention , of all the phasers I've owned and played , I've never heard a small stone in person , knowingly.    I've built just about every major phaser but the only ota I have is the Ross. I assume very similar sounding

(don't know what all this tells me but at least to determine that the 4th one is good I guess)

[R.G.]

If I were you, I'd replace the 3094. You could use a 3094, or you could hack in an LM13700 for two of them by dead-bug mounting of the 13700.

[analog kid]

Hey RG! Yes I'm ordering a 3094 right now since I'm pretty positive that it's got some problems and that it's only that one.  I don't know enough about the IC but it just seemed odd to me that the 'wobble' is there within that stage BUT JUST Low gain so that it pretty much completely nulls the wet / dry mix at the output

I will get it on it's way and I hate to even put a socket in so to keep it original but I don't know if I can bring myself to buy a $5 ic and not socket it, yeah I'm cheap.    Although just to "hear it work" in the meantime I was thinking that as well , that I DO have some extra 13700's  and they might serve the purpose.  I guess I need to look at data sheets but if you want you could walk me thru the pinout to wire it for wiring one in to replace a 3094 here.   I assume using only half of a 13700 will replace the 3094.  I don't care about temporarily wasting half the ic if so.   I'd rather do that than desolder another 3094 that doesn't need to be.

Thanks

[StephenGiles]

I would order 2 in case another is not quite the ticket!

[analog kid]

Ah! I already ordered just one with Steve.  but I am cheap as I said. can't bring myself to pay 10$for two ic's if I only need one. I am fairly sure that I have confirmed it's only the IC3 stage with a problem (if it even is the 3094 , but I can't imagine what else) by jumping a stage from 2 to 4 and all is fine when IC 3 is out of the 'chain'.   I don't though know what's going on with the other 2 3094's that are NOT in the LFO , at the bottom of the schem. So I am only assuming there that those are AOK.   
  It's bad enough for originality if I'll have to replace one of those house EH ic's but gotta be done sometimes.   btw there aren't any markings left on any of the IC's in mine, if they were even house marked at all as stated in the schem. Hmmmm... and the unit looked as if never touched inside.  I am wondering if somehow the grey foam breaking down  in there could've done something like that even though not facing that side?

[puretube]

those 2 are the LFO... (A5, A6)

[analog kid]

Uh... 
  well I guess since the lfo is going that I DO know that they're ok then.  I don't know what I was thinking  I should obviously know that since the IC1-4 are the phase stages , they can't be phase stages and the lfo,  so those have to be the lfo. duh .  I think I said that cause Pin5 of each ic has the lfo on it.

  I'd love more info on what RG mentioned of replacing 3094 with LM13700  ( 1-2 x  3094) guess the lfo would be a good place to use an "LM" as sub then.   But I do have only one 3094 coming for this and I guess I"m hoping that the IC3 is ACTUALLY Bad. but based on the TS technques I used stated here, I don't see what else it would be going on within the third stage to pull down the Gain so much and throw the voltages off (down) OTHER than the IC getting weak itself.  (?)
though I've read I believe that it's unusual for just ONE IC to bad like in this circuit (or any ) due to a  misvoltage, wrong polarity ,etc.. so if it's bad maybe from something else.  I'll basically be amazed if a new 3094 doesn't do it.   And I guess I should use a socket there but I really like things to look as original as possible.  I've never NOT used a socket for a several dollar I c though

[Gus]

Before hacking the 75 small stone up(It might be worth some money being ).

I would change the LFO electro(save the old one) if that does not fix i

  I would put it away for some time and build a new small stone.  Then maybe try to  fix it again.

The value of hacked up old effects is not as much as ones that are broken and have not had an attempt to fix them

I have bought or worked on effects that someone did more damage with the "fix" than the first damage.

Things like a real biphase that not much money was spent on that had some real damage from the person before that tried to fix it.

[analog kid]

"it might be worth some money being"

   what do you mean by that?
 
thanks gus,  are you suggesting I change the LFO Electrolytic(s) for this issue with a weak / dead phase stage IC??  And if so why? the lfo as far as I can tell is working fine.  Also I assume that's the 1uf Tant (one of the neat little 'seconal' looking ones too ) you're talking about and boy I hate to be disturbing that one if there if the symptoms don't point at it.
secondly I am definitely doing NO hacking to this ol thing by any means. I don't consider lifting a few resistors , audio probing and temporarily jumping new components to sections of the circuit hacking or potential to damage at all.  Of course as Long as one knows how to treat desoldering resistors,etc.. And I'm sure most folks don't consider reflowing all solder joints any undesireble attempt at repairing a unit.
 

I would put it away for some time and build a new small stone.  Then maybe try to  fix it again.

Uh, so you don't think it's obvious from all I've noted here from going over the unit that it's definitely an issue with the IC3 stage(the IC itself) I don't see how it couldn't be nor do I see how something in the lfo(ie; electrolytic) could affect this stage this way , messing up voltages here and dropping gain.  ? but I'll take your suggestion and maybe try a fresh cap for 1uf tant, def if somehow my new IC doesn't fix things.
anyway the only thing I plan to do at all at this point and based on the creative "troubeshooting" I did, I believe this will be all it needs to be like new again, is to replace that IC3 with a new 3096 . So that should be the only thing making this unit NOT all original i  am hoping.
Oh and I don't need to build another smallstone. I just enjoy having ORIGINAL units. I revived a first model '76  Electric Mistress awhile back which the 741 IC regulator section went bad in. I got it for $42  It is a GEM.  And as far as hacking up vintage fx goes with me, I will hardly true bypass unless It's a real 'sucker'and i'll be gigging exclusively.

btw if THAT is the reason you advised about "hacking it" ,  I was just asking about the LM13700 sub for 3096's just for educational purposes or maybe worse case if more ic's went bad and I couldn't get more anytime soon , NOT something I was really planning to do.   
I know what you mean about value though,  I bought this one as a not working unit which I made sure had no attempt to fix it!   A biphase huh? yeah , the more complex the device the more 'damage' likely to be done by someone just fumbling through hoping to get lucky in attempt to fix the problem!

thanks , I'll keep you updated