PLEASE Help with a MXR 118 Vintage Delay - IC pin Voltages

[Govmnt_Lacky]

does anyone know how to add a picture to post ? the "add image to post" is not working?

https://www.diystompboxes.com/smfforum/index.php?topic=60421.0

[jimitrader]

https://www.aronnelson.com/gallery/main.php/v/Schematics-etc/delay-board-118-web.jpg.html?g2_imageViewsIndex=1

i followed the signal from ic 1(4558) in pic back to this 2n4126 (0.88) could that be the problem a faulty transistor?

4016 #1 (next to #1 4558 in pic i posted)

   
• 0.71
• 0.16
• 11.32
• 0.12
• 0.04
• 1.38
• 0
• 5.62
• 0.12
• 0.10
• 0.74
• 0.02
• 0.03
• 12

4016 #2

   
• 0.78
• 0.02
• 0.03
• 5.24
• 0.03
• 0.03
• 0
• 11.98
• 0.02
• 0
• 11.32
• 0
• 0
• 0.80

[idy]

You refer to a "pic" or picture of your board....not posted?

If in fact the schematic posted now has any connection to your unit (sounds like we are talking about the same chips):

The signal input should go through both halves of that dual opamp before it hits anything dicey...and I do not see any transistors in the signal path until....

Actually, the only transistors I see on the schematic are 3 servicing pins 8 and 12 of the Reticon. Someone more knowledgeable will have to explain what they do. They are attached to "even out" and "odd out" of the BBD.

If you are absolutely intent upon touching that Reticon be careful...oh you already...You would want to find out if signal is getting to it. That would be pin 4 "analog input."
Anybody know how to explain "careful with the BBD?"

Both halves of the first opamp (IC2)....must...be....signal there.....After that, the 4016 you will have to think about....The 4016 controls bypassing the actual delay "machinery." I think. (IC 1a does the mixing/buffering dry/wet before output I think...
If you are still getting clean signal passing through on bypass yes? If so IC 2a, 2b, and 1a MUST be operating.

[jimitrader]

the board pic is a link
https://www.aronnelson.com/gallery/main.php/v/Schematics-etc/delay-board-118-web.jpg.html?g2_imageViewsIndex=1

[jimitrader]

   
• what is the size of the big capacitor near the transformer? the schematic is so blurry i can hardly read it

[idy]

That's news. What transformer? Can't see it in picture. Can't see in in schematic. Schematic shows 9vdc jack..
And next to that jack a 400...that would be 400uf. But again, can't be your problem if power is present at chips etc..
Maybe you are poking around a transformer for fun... Stop that.

You didn't address any questions above:
Signal at both sides of IC2, at least one side of IC1?
Signal at pin 4 of Reticon?

[idy]

Maybe I see the transformer, under the board? There is a big cap near it (normal), but you can read it, we can't. It needn't be the same value is the one on the schematic.

But again, if it is passing sound, it is getting power.

Are both halves of IC2 getting sound? and one half of IC1?

Not to change subject but to clarify: This is not a true bypass pedal is it? It uses a CMOS quad switch yes? So the foot switch is probably single pole....?

[idy]

And also to clarify: the 2n4126s (there are two) are part of the clock circuit. No way on this green earth any one would expect to find audio signal on them.

[Govmnt_Lacky]

OK... I think this topic is kinda going off the rails and needs some course correction 

1st: We need to ensure that we are all working off of the proper schematic. Lets do that. We need to answer a few questions:

- Does your MXR M118 have a power adapter (wall wart) -OR- does it plug directly into the wall (3-prong plug) for power?
- How many IC chips does it have and what are they labeled as? (See below)

2nd: We need a PROPER list of voltages

- Re-post your voltages for every IC with pin numbers AND ensure that the ICs are numbered according to the PROPER schematic.

I believe the ICs are numbered and identified like this (feel free to correct)

U1: 4558
U2: 4558
U3: 4558
U4: CD4016
U5: 4558
U6: CD4016
U7: CD4013
U8: CD4001
J1: R5101

You will need to take some readings with your multimeter to confirm this but, THIS is definitely where you need to start AND once you confirm the ICs against the schematic then you can list proper voltages and we can go from there 

[duck_arse]

there is two types of lists provided - the one above is "Unordered" - it gives bullet points, the one below is "Ordered" - it numbers the entries. I think the type=decimal attribute can be changed to produce roman numerals instead. but I dunno the code. css.

• eye
• vee
• eggs

[jimitrader]

Thanks

[jimitrader]

Govmnt_Lacky
I agree...thank you   This MXR M118 does  have a power adapter (wall wart)  YES
here is a new picture with IC's listed... first lets make sure i have the order correct before moving on

[idy]

Without seeing the bottom of the board and doing a trace it is hard to be sure which 4558 is which. Trying to read all the (legible) cap values and guess which 4558 they are attached to is slow going. And one can't read the larger value (probably tantalum) caps at all. Or the red film caps. Reading resistor color bands from photos is also dodgy. You can see some traces through the board...but not enough.

Briefly: we can't trace it from only one side of the board...But we don't need to completely trace it to begin debugging!

So I suggest doing what we have been saying:

post voltages for all the chips again using your provisional numbers.

Since you started to signal trace, you can do that also. Is signal getting to some of the 4558s? (It seems like your choice for 4558 1 and 2 were right before.) Which ones, which pins? Is it getting to pin 4 of the Reticon?

[Govmnt_Lacky]

Here is a formal list of what YOU need to do in order for US to help:

1) Establish which schematic we are working from (DONE)
2) Match the ICs on the circuit board to the numbers on the schematic (YOU will need to do this. U7, U8, and J1 are easy because there is only one of each. The others will need to be sorted by using your multimeter and doing some continuity testing or following traces on the back of the board)
3) Take voltage measurements on the IC chips.
4) Post the voltages on each pin of the ICs and number the ICs according to the schematic.

[jimitrader]

in this pic #4 4558 is where the sound dies out no audio on probe past this area? going to re-do all pin voltages in a minute...BRB

[idy]

That should help! I think:
the one you marked "4" is really U1.
the one you marked "2" is correct!

How I "know": one most common use of opamp is buffer: pins 1 and 2, or 6 and 7 are tied together. The schematic shows:
U4 and U3 have both sides as buffers
U2 has only one (pins 1-2)
U1 has none.

Looking at the traces you can see this. the one you marked U2 has one buffer. The One you marked 4 has none.
Next is to sort out which of the ICs marked 1 and 3 is  3 and which is 4.

[idy]

Hints: The real U3 has two 4.7k resistors attached to pins 3 and 7, and a 10k to pin 5.
The real U4 has (here the schematic is pretty blurry) 5.6k(?) to pin 1, 6.8k(?) to pin 3 and 3.3k to pin 5.

The real U4 has two .001 caps connecting it to a 4016.

[jimitrader]

thank you! i am going to dig in to what you have told me here and report back..  i got side tracked yesterday ...argh...will update later today...

[jimitrader]

I am going to come back to this pedal later...i need a break from it...thanks everyone who tried to help me.

[pinkjimiphoton]

Just as a heads up for this pedal.....

The R5101 BBD chip is notorious for going bad. I was/is horribly susceptible to ESD damage. Definitely do your best to protect against this. Also, this chip is LONG out of production and very rare to find available. Hopefully it is still good.

Good luck! 

greg nailed it. 99% of the time with one of these, if its passing signal, its the reticon chip that is dead and irreplaceable. pull it out of its socket. if the other voltages suddenly get right, that means the chip is dead. hate to bear bad news, but usually, these end up being toast.