moog mf104

[Frances Rhodes]

hey y'all

i recently bought a used mf104 (not the latest one with tap tempo nor the limited edition with longer delay time), #0288 if i am correct, and i'm having some problems with it.
the bypass "pops" every time the switch is pressed, and the "pop" is almost as loud as the guitar sound, doesn't matter what settings i choose on the pedal (gain, volume, etc), and it is also very noisy (and the settings do matter this time, the more delay bended in, the louder the noise).

would anyone have an idea of what to do to "cure" the pop problem? i opened it to have a glance inside but without the schematics i am clueless of what to try.
also, if anyone knows where to find the schematics, i would be a really happy man! (and if it is needed i'm willing to pay for those schematics, although i would prefer not to  )
about the noise, i guess nothing can be done since i know BBD chips to be noisy, but we never know, so i'm all ears!

thanks in advance
regards

frances

[PRR]

> what to do to "cure" the pop problem?

function, may do better with Advanced Search, "POP", last few months (200 days).

http://www.diystompboxes.com/smfforum/index.php?topic=108004.0
http://www.diystompboxes.com/smfforum/index.php?topic=108149.0
http://www.diystompboxes.com/smfforum/index.php?topic=107399.0
http://www.diystompboxes.com/smfforum/index.php?topic=107407.0
http://www.diystompboxes.com/smfforum/index.php?topic=107693.0

[tombaker]

Moog products are notoriously hard to find schematics for and when you do find them or reverse engineered schematics, they splatter your brain all over the walls.
Well mine anyway.

http://www.moogmusic.com/sites/default/files/MF104M_Interior_Final.pdf
This is the closest you'll probably find, which has a circuit/diagram which may help or may not.

http://www.moogmusic.com/sites/default/files/MF-104Z_man.pdf
This could also be what you're looking for depending on which version it is.

But like PRR said check out all the other "POP" related posts and whenever I'm poking around inside an old or second hand pedal I usually clean the pots and switches as this may help with any residual movement noise not directly related to the "POP".

[alanp]

Tried emailing Moog Music? Couldn't hurt.

[Frances Rhodes]

thanks for all the answers

Paul - i checked those links but, unless something like a blocking capacitor burned, i'm having a hard time thinking it could be a DC sent to the next input stage (since it pops even when the input is left open, in several different amps, it can't be my guitar, or anything i plug into it), and since it's a moog pedal, i want to believe it's strong enough not to break! or maybe i'm too optimistic cause obviously, something went wrong!!!

Tom - thanks for the links, i checked the 104M diagram, if i believe what i read (and this diagram is the same for my 104Z without the LFO part), there are no electronic circuit after the output pot when engaged or after the input buffer when bypassed, so i could try to identify the blocking capacitors right before the output jack to see if they still do their job... if my brain doesn't cease to work before!!

Alan - i'll try that, but i already tried their forum and didn't find much information there unfortunately, but thanks for the idea!

frances

[tupinamba]

Hi!
I'm wrinting in this topic because it also concerns a MF-104.

I bought one second-hand one week ago. The seller told me that the "long" delay did not work, but the "sort" worked perfectly. That was right. So I tried to find the issue and suspected the 4016 (bilateral switch). I noticed that by connecting pins 1 and 2 ("switch 0" of the 4016), the long delay worked perfectly. But i did not want to push my luck so I did not bridge them.

The very next morning, as I wanted to hear again that beautiful delay sound, I plugged it back and then...I noticed I had a VERY weak output with the delay mix, while the dry output was still OK. I could hear the delay, but it was far, far away!

Since, I have checked the daughter board connections (it is often an issue as it seems), but in my case connections are fine...

I haven't changed the 4016 yet, but I think I'll try that. But I'm thinking it must be some kind of amplifier somewhere (OpAmp failure?...)

I've made a list of all ICs in the circuit (maybe someone can find a "usual suspect" in that list):
MAX761CP
TL072CP (x4)
TL074CN (x2)
LM13700N (x4)
CD4053BE
CD4049UBE
CD4024BE
LM324N
MN3101
MN3008 (x5)
LB1405 (x2)
LM311N
SA572N
CD4016BE

The thing is, without the schematics, it is really hard to find where the problem might come from and to trace the signal path...

Anyway, all help welcome here : schematics, tech advice...

Thanks in advance!

[Frances Rhodes]

unfortunately, moog schematics are classified "intellectual property", there is no way you can find any of them unless you become an ingeneer for moog.

at this time i still haven't found anyone to help me fix the problem on my pedal, or a professional electronician sponsored by moog to have it done, and i still can't use it!

[tupinamba]

Damn...
I tried and replace the 4016 switch, but it did not change a thing to my issue. I may try to replace all Op Amps just to be sure. It doesn't cost much...

[Frances Rhodes]

no it doesn't, but if i remember well, most of them aren't mounted on sockets, so, unless you have a hot air-blower, i wouldn't recommend trying!

[tupinamba]

You're right if you're trying to save the components in case they aren't damaged. But what I do with cheap, replaceable components, is that I cut the legs and then carefully unsolder each leg. This way you don't damage the PCB and traces!
I think I'm going to change the LM311 (voltage comparator) first. I think it may be the IC that deals with volume mix (as the "MIX" pot doesn't deal directly with audio signal).

[tupinamba]

The LM311 replacement didn't solve the problem.
But while tracking the signal path with a probe connected to an amp, I created pops that delay with no volume issue (probing the TL074 ICs), so I think that the issue may be BEFORE the delay chips and after the dry signal out.
This narrows things a little...

[Hatredman]

Keep us posted with gutshots.

[tupinamba]

Your right Hatredman ! Sorry...

Good news though : today I replaced the 4053. I was tracking the signal and it seemed to be a possible suspect. I did not change anything at first and I continued the "reverse engineering" process, sometimes soldering a piece of component leg to be able to grip it more easily... And a miracle happened. Delay signal is back at its full volume!

I don't know if I accidentally cured a weak solder joint, or if I made a small short-cut that reset a logic component... But delay's back and that's a great news!

I still have to solve the "long delay" issue : still a pop, half a second of long delay, and then nothing... (unless I bridge pins 1 and 2 of the 4016...)



SW2 (top 6 big solder pads) is the DPDT switch to change from "short" to "long". It leads to the 4016 (socketed 14 pin IC on the right, above the red cap), but I changed this IC and the problem remains.

The weird thing is that I can actually hear it (and mod its time) for about half a second before it turns to nothing. Something seems to block the signal...

[tupinamba]

Hi everyone!

Four years later, back to this "long" delay issue... It's happening here :
https://www.diystompboxes.com/smfforum/index.php?topic=123079.0

Cheers!

[Frances Rhodes]

Hi!
Funny seeing this topic raised from the dead !
I still have big problems with mine, which happened to have gone from "pops when I switch it on" to "mix output is dead silent".
I'm guessing one of the OTAs burnt, but I don't know how to test them, and they're a bit pricy to just desolder them all and replace them with new ones, and throw the old ones away.
The thing is the delay output works like a charm, but to use it like that, I'd need to make a blender, which is quite a bummer...

[tupinamba]

Yeah, topic raised from the dead... But I'd prefer the MF-104 itself to raise from the dead (although mine is not really dead. In limbo, maybe...)

I'm trying to trace the signal path around the "Short / Long" switch. It is a DPDT, in "Long" position one signal is going to the CD4016, the other one it going to a LM13700. The weird thing is that it's connected to pins 5 (output 1) and pin 13 (negative input 2). The only application I found in the datasheet where output 1 is connected to input 2 is for a "logarithmic current source", but with the positive input 2 (not the negative). And it doesn't explain why it would be connected to a switch...

Working without schematic... 

[Frances Rhodes]

unfortunately, that is beyond my understanding...
if you could draw a scheme, maybe someone could help more than me!

[Scruffie]

Yeah, topic raised from the dead... But I'd prefer the MF-104 itself to raise from the dead (although mine is not really dead. In limbo, maybe...)

I'm trying to trace the signal path around the "Short / Long" switch. It is a DPDT, in "Long" position one signal is going to the CD4016, the other one it going to a LM13700. The weird thing is that it's connected to pins 5 (output 1) and pin 13 (negative input 2). The only application I found in the datasheet where output 1 is connected to input 2 is for a "logarithmic current source", but with the positive input 2 (not the negative). And it doesn't explain why it would be connected to a switch...

Working without schematic... 

Like, a buffer...?

[tupinamba]

Yeah, maybe a buffer...

I've started to work on making a schematic. I've posted its current (basic) state on this new topic I've created (but actually you guys are replying here :-) )

https://www.diystompboxes.com/smfforum/index.php?topic=123079.0