Fender - Yngwie Malmsteen Overdrive

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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mirosol
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Post by mirosol »

I've got your messages. In plural.

I got ~99% of my pedals stashed away in plastic storage boxes for a few years now. Mainly due to having moved from ~200m2 house to a studio apartment. I'm sorry but i'm not going to go those boxes through to find this one right now...
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Manfred
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Post by Manfred »

I started an approximated PCB clone to find the circuit by tracing it. Unfortunately not all traces are visible on the top side.
Are there more snapshots where more can be seen?
FYM OD Layout.JPG
FYM Tracks Componets.jpg

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george giblet
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Post by george giblet »

Here's as far as I got. Run out of time.
Have not check against Manfred's PCB tracks.
Fender - Yngwie Malmsteen Overdrive Draft V01.png

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Manfred
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Post by Manfred »

Hi George,
thanks for drawing the schematic, i was just about to start it myself and saw that you already did it, great.
I retraced the circuit using the layout and can say that the signal path is correct.
Only the op-amps were reversed from the terminal designations.
I corrected the circuit around Q3.
With the circuit around Q1 and around C10, C9 I am not sure, because the course of the traces on the top are not completely visible.
I found this DOD circuit below, which was very helpful because of its similarity, because I could enter the designators and values of the components there.
With the R4 = 10M at the input I am also not sure.
Fender YJM OD Layout V2.JPG
DOD308YMJEsquema.jpg
Fender YM OD Traced Circuit.jpg
Fender YJM Schematic V1.jpg

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george giblet
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Post by george giblet »

I retraced the circuit using the layout and can say that the signal path is correct.
Awesome Manfred, thanks.

I'll probably do another pass myself, normally I do that. I was a bit rushed, tried to get a schematic up before doing something else :).

I probably won't be able to have another look until tonight.
Only the op-amps were reversed from the terminal designations.
Thanks for picking that up. I drew out the schematic on two *small* pieces of paper and screwed up when I transferred it onto the computer.
I corrected the circuit around Q3.
With the circuit around Q1 and around C10, C9 I am not sure, because the course of the traces on the top are not completely visible.
I found this DOD circuit below, which was very helpful because of its similarity, because I could enter the designators and values of the components there.
With the R4 = 10M at the input I am also not sure.
All those areas are tough because I can't see anything either.

For Q3, the resistor R12 could wired in three ways:
- R12 from gate to +V, then the footswitch shorts the gate ground
- R12 gate to ground, then the footswitch pulls the gate up to +V
- as shown, where the footswitch would need to connect R12 to +V and gnd.

If we can work out if the footswitch contact has +V and/or gnd connections then we might be able to work out which option is the most likely. Just looking a the layout it seems R12 to ground would work.

Early on I had R12 across the output socket. I moved the R12 connection after tracing Q3. I just had a quick look at the PCB and maybe that was correct after all: On the bottom layer: R12 connects to ground and the output socket "tip" (unswitched contact). After doing that, I can see there might be an R19 (not on any parts list or the schematic) which connects from the gate of Q3 to +VA near the LED socket.

For C9, C10, I spent more time than expected on that area. You have to look at a lot of pics to workout where the tracks go. I have some confidence the schematic is very close.

R4 is only my best guess.

FYI, the PCB links R9 and R10 on the top layer. You can just see it in one of the photo in the thread.

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george giblet
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Post by george giblet »

Just to keep the ball rolling.

The missing part under the output socket isn't a resistor R19 but a diode D4 - which is in mirosol's part's list.

I've patched how I see the footswitch and socket wiring onto the schematic.

Not sure if C7 connects directly to the input socket or to the effect input.

It really looks like R12 is permanently wired across the output socket.
That means it's going to load the pickup in bypass mode.

Any comment or criticisms welcome. Some of this is my best guess.
Fender - Yngwie Malmsteen Overdrive V02.png

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Post by Manfred »

Great, a millenium bypass was also my guess. :thumbsup

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george giblet
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Post by george giblet »

The top part of the switch still isn't correct. If the input socket goes to the switch pole/common and the effects input (IN) goes to the top contact it fixes up the switching. However, I'd like to see the PCB tracks implying the same connection. The general idea is there but the details are hard to confirm since the tracks aren't visible.

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george giblet
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Post by george giblet »

Here a bit more.

A few minor changes to the schematic, and first revision
Fender - Yngwie Malmsteen Overdrive V10.png
Possible tracks. However the part in the green circle might be flipped and
one of the tracks could go around the top of the switch.
pcb pic - markup.jpg
Couple of tracks on the layout:
Fender YJM OD Layout V2 - markup.JPG

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Manfred
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Post by Manfred »

Thanks Georg for your patience in figuring all this out, great. :worship:
I am not satisfied with the value of C12, I guess this should be more like 47uF.

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george giblet
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Post by george giblet »

Thanks Georg for your patience in figuring all this out, great. :worship:
I am not satisfied with the value of C12, I guess this should be more like 47uF.
Thanks, tracing boards with missing pieces is tricky. I think we just barely scraped in on this one.

Also lucky - one of the images in the second lot of PCB pics has C12 peaking out over the pot.
c12 value peaking out.png
c12 value peaking out.png (167.92 KiB) Viewed 434 times

(The main power is a little flimsy on this unit, 100R series resistor and a 100nF cap.)


Forgot to mention before, C7 looks like it is in fact permanently connected to the input socket.
I haven't shown the battery -ve switched by the input socket either.

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Manfred
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Post by Manfred »

Thanks!
I see you have a sharp eye and a lot of patience.
The issue with the C12 would then also be clarified.

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george giblet
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Post by george giblet »

For the sake of putting as much of what we know down on the schematic,
I've make C7 permanently connected to the input socket.
I'm going to drawn the line there until someone says otherwise.
Fender - Yngwie Malmsteen Overdrive V11.png

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Post by Manfred »

I'm going to drawn the line there until someone says otherwise.
I agree it is done.
I considered drawing the missing traces into the layout but decided against it, since their true course is not visible.

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george giblet
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Post by george giblet »

Manfred wrote: 26 Jan 2023, 11:03 I considered drawing the missing traces into the layout but decided against it, since their true course is not visible.
Yes, it's going to be hard to resolve without someone going over the connections with a multimeter. Even then we won't know where the tracks actually go. It's taken over 7 years to get to this point!

It's interesting the Fender Version is different to the DOD version.

I wasn't sure if the second schematic you posted earlier was for a DOD pedal. I recognized the first schematic as DOD but I don't remember the two opamp version.

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Post by Manfred »

In the end, the circuit of the signal path is the most important,
the LED control and the reverse polarity protection can be replaced by other circuitry.

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