Small Stone Repair

michael_krell · August 10, 2004, 03:48:06 PM

Upon further investigation I noticed I did have the stages messed up. the signal drops down in the last 2 stages. hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

its just a matter of time now before I get this puppy back in order.

michael_krell · August 10, 2004, 04:49:18 PM

I have a dumb question that I know i will get a quick scolding for but is there a direct replacement for the EH1048 IC?

gez · August 10, 2004, 05:11:03 PM

Quote from: michael_krellis there a direct replacement for the EH1048 IC?

According to the schematic, the CA3094 is a direct replacement and Small Bear sell them

http://www.smallbearelec.com/Ordering/Stocklist.htm

First though, take some voltage measurements for the last two stages and post them (particularly pin 6 of each chip, but also check power connections and the voltage on the inputs)

puretube · August 10, 2004, 06:42:31 PM

...and triple/quadruple check the surrounding R & C values AND the solder joints - got the strong feeling it`s NOT the ICs (although that`s still possible...)
(we had the: "I modded my RI SS recently with the volumedrop-mod - it worked for 3 weeks, now it`s dead" problem on HC forum 3 days ago, and reflowing the pads that held the swapped resistors, was the solution...
- it was the 1st proposal...)
:?:

PS: the EH1048 was just a re-(custom-)stamped CA3094, like GEZ pointed correctly

michael_krell · August 10, 2004, 09:08:49 PM

Here is my progress so far. The input to the first 3 IC's seems to be real low and the signal doesnt look very clean. The output of the 3rd IC looks like its where it goes sour. The output is very low and it looks like just noise or a really really low signal. could the 3rd IC be bad and have a short that grounds the signal???

puretube · August 11, 2004, 02:56:18 AM

we tried to rule out that chance, but it is possible...
also, it`s not sure, whether the 4th one works, or also is defective.

(sorry, will be offline for a while...)

gez · August 11, 2004, 03:44:53 AM

Quote from: michael_krellThe input to the first 3 IC's seems to be real low and the signal doesnt look very clean. The output of the 3rd IC looks like its where it goes sour. The output is very low and it looks like just noise or a really really low signal. could the 3rd IC be bad and have a short that grounds the signal???

The signal is divided down at the input so it will seem low. Although there's negative feedback, it's not in phase with the original signal so a voltage develops at the input - if you pulled the parallel cap you should see (I've never built a SS) the 'virtual ground' effect. Change the division on your scope so that the signal appears larger on the screen, this will probably make it less distorted and will give you a better idea as to what's happening in the last two stages.

What's happening at the outputs of the first two stages? Although the inputs will appear low, the outputs of each stage should be the same amplitude as the original signal.

Post some (multimeter) voltages for the last two stages.

As PT said, although it can't be ruled out it's unlikely to be the chips. Why would they suddenly fry? (unless someone has 'modded it') They're not CMOS or anything, if they have 'gone bad' it's for a reason...look for signs of tampering.

michael_krell · August 11, 2004, 08:58:43 AM

are you saying the output on the last 2 IC's are supposed to be low??

puretube · August 11, 2004, 09:42:44 AM

no - all 4 the same at their corresponding respective in-/outputs -
gez wants to know the DC levels, to see if those last 2 are different...
(best measured with no input signal to the pedal).

- going on vacation tomorrow -

gez · August 11, 2004, 12:05:13 PM

Quote from: michael_krellare you saying the output on the last 2 IC's are supposed to be low??

Not at all, you mentioned that the signal at the inputs seemed low (and by input I mean the -ve input of the chip) and I was pointing out that this is normal as the signal is divided down (see above post). However, the amplitudes of the signal at each input should all be equal (as PT points out) and also the signal at the outputs should all have the same amplitude (which should be the same as that of the input signal from your generator - it shouldn't be smaller).

If you could post the DC voltages at inputs (+ve and -ve), output and power connections for the last two chips it would help. Use a multimeter or your scope even, but without an input signal. We need to know how they've biased up, this will give us a few clues (hopefully) as to why they're not working.

gez · August 11, 2004, 12:14:01 PM

Quote from: puretube - going on vacation tomorrow -

Bon Voyage!

michael_krell · August 11, 2004, 01:18:07 PM

Ill get on that right away, hopefully I will have results shortly.

michael_krell · August 11, 2004, 02:16:27 PM

Here are the results I found

+IN -IN OUT
IC1 2.5 2.5 2.5
IC2 2.5 2.5 2.5
IC3 2.5 2.5 1
IC4 2.5 2.5 1

Looks like the DC voltages at IC3 and IC4 output is 1Volt while all other DC votlages read 2.5

Let me know if that helps

gez · August 11, 2004, 02:57:09 PM

Quote from: michael_krellHere are the results I found

+IN -IN OUT
IC1 2.5 2.5 2.5
IC2 2.5 2.5 2.5
IC3 2.5 2.5 1
IC4 2.5 2.5 1

Looks like the DC voltages at IC3 and IC4 output is 1Volt while all other DC votlages read 2.5

Let me know if that helps

What did you use to take the readings? If it was your scope are you sure you got the right division? If you look at the schematic there's a divider that sets the voltage reference to half the supply. There are also little signs at the +ve input which tell you that the voltage should be 4.5V too.

If the readings are right then check the values of this divider (two 10k resistors across the rails) to see if someone has subbed in a wrong value for one of them.

More likely your readings are out (multimeters are far less faffing about when taking DC voltage readings - appologies if you used one of these). Assuming they're wrong then at least all the voltages of the first two chips are equal (suggests that these two stages are fine)

puretube · August 11, 2004, 02:59:33 PM

if you`re good in de-soldering ICs: take out the 2nd and 3rd,
put the 3rd into the place of the (former) 2nd;
if it still measures 1V @ OUT, it`s defective,
and the 4th IC probably too....
If you measure 2.5V, now it has changed place: there`s something wrong with the components/traces surrounding the area of the 3rd IC, and probably around the 4th...

gez · August 11, 2004, 03:23:39 PM

Whoops! I was looking at the wrong schematic (Ross Phaser) - sorry!!!! :oops:

All the readings should be the same, so it does suggest that last two stages are a bit iffy. Follow PT's advice if you can.

Sorry again...

michael_krell · August 11, 2004, 03:50:17 PM

i have some IC sockets so when i desolder the chips ill put those in to make my life alot easier.

michael_krell · August 12, 2004, 12:14:54 AM

Hey guys heres the story. I took out all the IC's and i put in sockets. I put each IC in the first IC socket and IC1 and IC2 tested fine. They both had the proper amplitude and "danced around" at the proper rate. The 3rd and 4th IC were a bit different. The 3rd one had no ouput at all and the 4th one had just a low output garbage. I already ordered some CA3094's from small bear yesterday on a whim and its a good thing because ill need them. Ill let you know of my status.

gez · August 12, 2004, 02:29:04 AM

keep us posted...

michael_krell · October 03, 2004, 04:41:39 PM

I just realized I never finished off this post. I put new IC's in that small stone and it works great now. There was 2 IC's fried for some strange reason. Thanks for your help everyone

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