I'm troubleshooting an mxr phase 90 and read that the 2 diodes in the power supply are a big reason for this pedal malfunctioning. I opened it up only to find that there is only 1 of the 2 diodes present. This pedal was bought in broken condition so it wouldnt surprise me if the previous owner removed it. I've also never worked with smd before so I'm having trouble grasping how it works.
(http://i1194.photobucket.com/albums/aa378/acrowemerica523/Mobile%20Uploads/20150822_200244_zpsxnz8nf3f.jpg)
(http://i1194.photobucket.com/albums/aa378/acrowemerica523/Mobile%20Uploads/Screenshot_2016-01-03-11-56-36_zpsicsox2m7.png)
The diodes in the bottom right hand corner of the picture appear to have 3 solder points. I have seen that some zener diodes have 3 solder points. Now im assuming this schematic is right and d1 is 1n914, but I cannot find a 1n914 smd diode with 3 solder points.
The pedal has the script logo on the front and seems to have been made in 2004.
Can anyone give advice on what should go in this spot?
The sender is removed, which just protects from power surges. Was the wrong voltage plugged in? If so, opamps are next to check with an audio probe.
SMD components sometimes have different part numbers the one you want is MMBD914 for the 3 pin 1n914
https://www.fairchildsemi.com/datasheets/MM/MMBD914.pdf (https://www.fairchildsemi.com/datasheets/MM/MMBD914.pdf)
You can get them at Mouser and Digikey
http://www.digikey.com/product-detail/en/MMBD914-7-F/MMBD914-FDICT-ND/717888 (http://www.digikey.com/product-detail/en/MMBD914-7-F/MMBD914-FDICT-ND/717888)
http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/MMBD914/?qs=1KwYHESJF3B2veQrbV1m7g%3D%3D (http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/MMBD914/?qs=1KwYHESJF3B2veQrbV1m7g%3D%3D)
D1 seems to be a reverse protection diode. the pedal ought to work without it. it could be replaced with just about any diode with the right pinout.
D2 is providing a stable bias for the circuit, and should not be/need messing unless it is carked.
probe the pads on the board with your ohm meter, see if the three D1 pads are actually connected to something. then look at some smd diode datasheets, and see the packages. the same part number, with a different suffix letter, can/will indicate 1 or two diodes in the same package, or one diode with only 2 pins connecting, or 1 diode with all three pads connected.
as an example:
http://pdf.datasheetcatalog.com/datasheet2/b/0dddqjdlya9kl26zhxkkqq2u6icy.pdf
[edit :] also, you probably want to ask a moderator to move this to the general section, as more people will see it there. some people don't like digital.
Quote from: jimilee on January 03, 2016, 02:09:39 PM
The sender is removed, which just protects from power surges. Was the wrong voltage plugged in? If so, opamps are next to check with an audio probe.
Checked the opamps with an audio probe. opamp's 1-4 are getting sound at the IN- and OFFSET N2 pins. However,1 opamp #5 is not getting sound. neither is either side of C9.
Checked the voltages and opamps 1,2,3,4 and 6 are all roughly:
pin1 - 0V
2 - 2.4V
3 - 2.4V
4 - 0V
5 - 0V
6 - 2.4V
7 - 9.1V
8 - OV
Most of opamp 5's voltages wouldnt give me a steady reading, they were...
pin 1 - 0V
2 - 2.5V-3.1V
3 - 2.5V-3.1V
4 - 0V
5 - 0V
6 - 2.1V-3.8V
7 - 9.1V
8 - 0V
So something with opamp 5 is really off.
Also thanks Mcknib and Duck_Arse, thanks for the info on the diode. I'll probably replace it since i'm fixing it for a friend just so its equipped with that.
You'll get the op amp expected voltages at GGG here for comparison:
http://www.generalguitargadgets.com/pdf/ggg_p90_instruct.pdf (http://www.generalguitargadgets.com/pdf/ggg_p90_instruct.pdf)
Schem etc here:
http://www.generalguitargadgets.com/effects-projects/phase-shifters/mxr-phase-90-script-logo/ (http://www.generalguitargadgets.com/effects-projects/phase-shifters/mxr-phase-90-script-logo/)
Not SMD but the same circuit I would think if you've got 6 x single 741 op amps.
As far as I know you wouldn't get any audio out of the LFO op amp which would have alternating voltages that would be the one connected from it's output pin 6 to the speed pot lug 3 your IC 5?.
You'd have the 1st op amp at the input, the input buffer section, 4 in the phase shifting stage and one LFO then your 2N4125 in the output mixing stage you should get audio at the input out of pin 6 through the phase stage op amps and also down and around up to the 150K resistor (R18 here.) both going into the base of the 2N4125 where the signals mixed and goes to the output something like this:
(http://imagizer.imageshack.us/v2/800x600q90/839/6qr9.png)
Please note this audio path was done some time ago and never finished or verified I'd imagine you'd also get audio on the feedback loops of the 4 phase stage op amp's but it follows the rule no audio on things going to ground or coming off 9v hence the 'something like this' - blue in this schem is phased and green clean signal
Anyway hope the info helps if you follow it from IN to OUT you should get an indication of your problem area where you lose the signal, you didn't say what type of signal you're getting out of the op amps is it phased on the phase stage one's? If not and the pedal was bought not working maybe the previous owner messed with the trimmer the phase range is very small on it, if you decide to try adjusting the trimmer make sure you mark it's original position first and move it in very small increments.
My advice would be to audio probe it first though!
just for fun - measure the voltages on the pins of D2. and the pins of the trimpot. then, for extra points, go around the board, find all the test points, marked "TP1" "TP2" "TPn", and measure the voltages there. they are test points for a reason, we just need to work out what the reason is.
IC5 volts look ok for an oscillator.
what is the part # on the row of fets, Q1-4, please?
mcknib - where does "VA" on R27 connect in your blue/green circuit, any idea?
Here's the full schem with the power supply R31 = 100R, C12 = 100u, C13 = 10n DA, I posted it just to give an idea of the audio path.
(http://imagizer.imageshack.us/v2/800x600q90/910/Imarfo.jpg)
IC1 = TL071, IC2 = TL074 and IC3 = TL061
I found that the signal goes the entire way through the pedal. With the pedal switched ON it is only slightly different than the dry signal (pedal switched OFF). No phasing effect happens anywhere in the "phased signal".
While probing the opamps I found that there is no signal coming from any of them on pin 6 but rather pins 1,2 and 5... as well as a faint signal on pin 3. They are indeed 741 opamps.
Is it normal that, when probed, all of the resistors and most of the capacitors in the "phased signal" only draw the signal on one side?
Quote from: duck_arse on January 05, 2016, 08:40:40 AM
just for fun - measure the voltages on the pins of D2. and the pins of the trimpot. then, for extra points, go around the board, find all the test points, marked "TP1" "TP2" "TPn", and measure the voltages there. they are test points for a reason, we just need to work out what the reason is.
IC5 volts look ok for an oscillator.
what is the part # on the row of fets, Q1-4, please?
mcknib - where does "VA" on R27 connect in your blue/green circuit, any idea?
The fets are 2N5952
2.4V on the side of D2 with one pin, 0V on both pins on the other side.
TP1 - 2.4V
TP2 - 2.3V
TP3 - 2.3V
TP4 - 2.3V
TP5 - 2.2V-3.9V
TP6 - 2.3V
You've got a distinct lack of 5v where it should be if you compare yours to GGG's D2 - 5v1 zener should give you 5v ish
I'm no expert but it does appear the lack of 5v is a major part of the problem and it appears to go back to pin 3 of IC1 which should be around 4.5v with incorrect voltages your FET's will be mis- biased giving incorrect resistances and no phasing you should have around 2v on the gate and 5v on the D and S from your readings your's will be 2.4 on the D and S
and just to double check are you reading your IC pins like this:
(http://upload.wikimedia.org/wikipedia/commons/b/b3/Pin_numbering_01_Pengo.svg)
mcknib - thanks, I was just a little unsure of the completeness of that dia. carry on.
also, I was about to say a 5V1 zener should not be reading 2V4, so something is pulling that down. but now mcknib has typed some, I don't need to. also, carry on.
No please do DA you're definitely a man of greater knowledge than me + I'm off to work sadly
Mcknib, you were right about the transistors voltages being off. I'm posting them for the sake of documentation.
Q1-Q4 =
D - 2.3V
G - 2.3V
S - 1.5V
Q5 =
D - .6V
G - 1.7V
S - 2.3V
I did notice that the trim pot on my pedal does not change impedance or voltage when adjusted. Tried every combination of the 3 pins. Is there a certain spot that the trim pot should be for the pedal to function right?
Quote from: mcknib on January 06, 2016, 08:28:44 AM
You've got a distinct lack of 5v where it should be if you compare yours to GGG's D2 - 5v1 zener should give you 5v ish
I'm no expert but it does appear the lack of 5v is a major part of the problem and it appears to go back to pin 3 of IC1 which should be around 4.5v with incorrect voltages your FET's will be mis- biased giving incorrect resistances and no phasing you should have around 2v on the gate and 5v on the D and S from your readings your's will be 2.4 on the D and S
The way you worded that makes me think the problem is somewhere in the power supply. Is this an accurate assumption? To diagnose the problem do I need to remove individual components and test them or is there an easier way?
Your power supply seems to be fine at 9.1v going in
Just for clarification use the GGG schematic and post voltages using their IC and Q numbers i.e your IC5 seems to be the LFO which is IC6 on their schematic Q1 to 4 would be the 2N5952's pins D, G, S and Q5 the 2N4125 pnp which would have C,B,E pins.
Do a continuity check on the zener to make sure it is the zener one side connects to ground and the other side should connect to pin 3 of the trimmer R22 in the GGG schem and to the + side of C6
apropo of nothing mutch: there was a recent discussion of why people hate tantalum caps hereabouts. one reason was they go short across supply lines, a bad thing. looking at yr first photo of the board shows a tantalum cap, right where a bypass for the Vref might be fitted. and, as you're seeming to be having some something dragging down your Vref voltage, like a short or low resistance where it shouldn't be ................
as they say, just sayin'.
Quote from: mcknib on January 08, 2016, 06:46:55 AM
Your power supply seems to be fine at 9.1v going in
Just for clarification use the GGG schematic and post voltages using their IC and Q numbers i.e your IC5 seems to be the LFO which is IC6 on their schematic Q1 to 4 would be the 2N5952's pins D, G, S and Q5 the 2N4125 pnp which would have C,B,E pins.
Do a continuity check on the zener to make sure it is the zener one side connects to ground and the other side should connect to pin 3 of the trimmer R22 in the GGG schem and to the + side of C6
The D2 didnt pass the continuity test. I am also getting 2v across the trimpot instead of 3v, so I am going to try swapping out one of those and a few capacitors/resistors. I want to get everything at once, but cant find a suitable D2.
From what i've found it needs to be a Zener diode that is 5.1V/500mW/sot-23(signifies the 3 pins)
I found some forums saying that the 500mW is important for it phasing correctly.
http://www.diystompboxes.com/smfforum/index.php?topic=22174.0
I could only find them with 300/350mW. I looked over mouser, digikey and the internet in general and found nothing. Could anyone provide me with a link or part #?
300 / 350 mW would be no problem in a 9v circuit, power dissipation or rating is a rough guide to how much power a component can take before it may fail or heat up dissapiting power it's not exact as far as I know.
When you say D2 didn't pass the continuity test do you mean there is no electrical connection from D2 to the 10uF tantalum capacitor + side (C6 in the GGG schematic) and pin 3 of the trimmer?
I would advise checking that cap first as duck_arse said rather than start pulling components out.
It may be an idea to post a complete picture of both sides of the pcb.
Quote from: mcknib on January 13, 2016, 08:00:29 PM
300 / 350 mW would be no problem in a 9v circuit, power dissipation or rating is a rough guide to how much power a component can take before it may fail or heat up dissapiting power it's not exact as far as I know.
When you say D2 didn't pass the continuity test do you mean there is no electrical connection from D2 to the 10uF tantalum capacitor + side (C6 in the GGG schematic) and pin 3 of the trimmer?
I would advise checking that cap first as duck_arse said rather than start pulling components out.
It may be an idea to post a complete picture of both sides of the pcb.
Forget the continuity remark in my last post. The grounded pin of the diode is continuous with the + side of the 10uf tantalum capacitor and grounded pin of the trimpot. The - side of the 10uf is continuous with the other (non-grounded) side of the trimpot and other (non-grounded) pin of the diode.
Upon closer inspection, the 10uf appears to have been resoldered back in place. Not to jump the gun, but would turning it around or using another aluminum electrolytic capacitor in the right polarity configuration be the next step?
Yes I'd try that any 10uF electro as you say in the correct polarity will do fortunately it'll be through hole so a quick one to try especially if it looks like it's been messed with.
Hopefully that'll be what's pulling your voltage down
DON'T turn it around. it is polarised for a reason, and it only goes in one way. it doesn't work better the other way round, it will melt/burn/go hoverboard on yo ass.
try pulling that cap out, and you can test for correct volts without it if you don't have a replacement at hand. or use a 4u7, or a 22uF, or a 33, 47, 100uF if you have one near. the value is not critical, same as the voltage of the zener is not critical, it just needs to be enough for your fets. you can go one or two voltage rating higher, again if that's all you can find. so, m a y b e 4V7 would do, or 5V1 or 5V6 or 6V2.
I ended up turning the capacitor around and the whole pedal BLEW UP
just kidding. It works now and most of the voltages are in proper range according to the GGG schematic. Except for these:
-Pin 6 of opamp's 2-5 is at 5V when it is supposed to be around 2V.
-The gate of Q2-Q4 are at 3.5V when they should be at 2.5V
-All of Q5 is down about 1V.
Plugged in, it sounds how a phaser should sound.
One additional question. I've noticed the trimpot on it still changes nothing tone, voltage or impedance wise when adjusted. Since its working,my first impulse is to box it and leave it be, but could there be an additional problem still here?
The trimpot should adjust the gate voltages on your FET's if memory serves -the phase range is very small on it but if you turn it too far you should lose phasing.
Begs the question with your voltages what make of meter are you using does it have at least a 10M input impedance? mind you must be ok if the rest are ok'ish
I'd be happy if I got it phasing so I'd box it up and keep it for a while to make sure nothing else goes wrong before you give it back.
duck_arse was right on the money
So I just got home and was doing some testing on the trimpot affecting the gate and the voltages suddenly dropped. Now I am getting
Q1-Q4:
G - .3V
D - 0V
S - 0V
Opamp's are drawing
Pin 1 - 0V
2 - 1.9V
3 - 0V
4 - 0V
5 - 0V
6 - 1.9V
7 - 9V
8 - V
Did a continuity check on the power supply/biasing section and both sides of the D2, trimpot and C9 are now connected to ground. Would it make sense that one of the 3 components (d2 , c9, trimpot) I mentioned shorted out and made both sides of all of the 3 components grounded. The "VB" section which meets the now grounded area meets the source of the FET'S would explain their voltage being at 0V.
I pulled out the c9 and both sides are continuous.
There is still one (out of three) non- grounded pin of the trimpot and one (out of three) non grounded pin of the D2 and D1.
ahhh, you had me for a minute there, but then .....
from your this diagram:
(http://imagizer.imageshack.us/v2/800x600q90/839/6qr9.png)
D1 sets "A" voltage dependant on its part number, whatever it might be. that voltage is then named VB, and should appear on C9 and TR1 (where their pins connect) and both ends of R3 (figure the meter loading, obvs.), and both ends of the R5, 8, 11, 14 and one end of C10 and Q5.
TR1 reads the VB volts, and a proportion of that appears on its wiper. THAT voltage (your choice, it's adjustable) appears on both sides of R30 (loading, again), and each of the fet gates, and one end of C10.
if you measure resistance from ground to the top of the trimpot, it should be 200k or something, can't see it at the mo. it might read different due to the diodes and the meter lead directions. if you read from ground to the wiper, it should vary up to your end-to-end reading.
if either the zener or that blasted C9 is bad (or the missing protection diode), it might be short/low ohms across the VB and ground, and will mess you up. take out C9. what happens to those voltages?
can we see a new photo of that corner of the board when you have removed the cap? (boy, I hope that caps bad.)
You don't say if you changed the cap - Did you put another replacement electro in there?
It does look as duck_arse says that your problem is somewhere on the VB line going by your initial voltages and your non-inverted inputs on the op amp pin 3's, FET gates etc. Hopefully it is that mo'fo' cap so again as DA says check the reading with it out.
With the diagram duck-arse is referencing you can see all your VB points which should obviously all be connected I'd be inclined to closely inspect the solder side of the board as well just in case the previous owner carried out some other work on it and bridged a trace or something.
Quote from: duck_arse on January 16, 2016, 09:06:06 AM
ahhh, you had me for a minute there, but then .....
from your this diagram:
(http://imagizer.imageshack.us/v2/800x600q90/839/6qr9.png)
D1 sets "A" voltage dependant on its part number, whatever it might be. that voltage is then named VB, and should appear on C9 and TR1 (where their pins connect) and both ends of R3 (figure the meter loading, obvs.), and both ends of the R5, 8, 11, 14 and one end of C10 and Q5.
TR1 reads the VB volts, and a proportion of that appears on its wiper. THAT voltage (your choice, it's adjustable) appears on both sides of R30 (loading, again), and each of the fet gates, and one end of C10.
if you measure resistance from ground to the top of the trimpot, it should be 200k or something, can't see it at the mo. it might read different due to the diodes and the meter lead directions. if you read from ground to the wiper, it should vary up to your end-to-end reading.
if either the zener or that blasted C9 is bad (or the missing protection diode), it might be short/low ohms across the VB and ground, and will mess you up. take out C9. what happens to those voltages?
can we see a new photo of that corner of the board when you have removed the cap? (boy, I hope that caps bad.)
The wiper of the trimpot reads between 62 and 63k and no amount of adjustment seems to change it. The wiper is at about 20mV.
With the cap out. The op amp and fet voltages are the same as they were with the capacitor soldered in, after it malfunctioned..
Q1-Q4:
G - .3V
D - 0V
S - 0V
Opamp's are drawing
Pin 1 - 0V
2 - 1.9V
3 - 0V
4 - 0V
5 - 0V
6 - 1.9V
7 - 9V
8 - 0V
(https://lh3.googleusercontent.com/-K6gJMyF3LDw/VprTNMFLS_I/AAAAAAAAAHQ/zjPSn-sPyX8/w346-h195/16%2B-%2B1)
(https://lh3.googleusercontent.com/-kK5iVCPmrrs/VprTIrRyU-I/AAAAAAAAAGo/sACjFiKjyNg/w346-h195/16%2B-%2B1)
I know my soldering is sloppy, however, it functioned for a while after I replaced the tantalum caps (with new aluminum electrolytic caps). And both polarities of the C9 were separate until the most recent malfunction. So I dont think I bridged a trace, although I could have. Also the stuff to the right in the picture is flux, not a scratch.Also if the picture is too small, dont be afraid to ask for a bigger one.
I have a slightly off topic question just for the sake of learning. You said that D1 sets voltage, wouldn't it be the R29 in the schematic setting the voltage for VB (voltage drop) since it connects straight from 9V?
search time for the frogman. RG and PRR have written of the dark art of zener diode usage hereabouts. read theirs so I don't give you the raw prawn.
basically, the zener is going to have 5V1, if so marked, across it, so you need to help lose the other 3V9 somewhere. a resistor will do this for you, quite nicely. the trimpot wiper then reads a proportion of that voltage, except in your case.
the picture is penty large, I just wanted to make sure you'd taken the cap out. your total loss of supply volts seems to be the major problem to fixxe, just at the moment. where did they all go?
So we've narrowed it down to the zener shorting, now I need to figure out why it died in the first place correct?
Would it be best to replace the zener, so that the correct voltages are present, then I could figure out what overloaded it? There is now only about 4mV across the zener.
I'm not sure that the schematic is 100% which is making it hard to envision exactly how I can trace the problem to the source.
Could just have been a power spike perhaps the previous owner used the wrong power supply or an AC supply or whatever I'd just replace it and see how it goes from there. That would be the best way to see if you get the correct voltages etc and see if it functions correctly.
The GGG schematic is probably the nearest if not the same as yours it being the script phase 90 so I'd use that for reference.
measure the value of the resistor in series w/ the zener. if it went funny (ho, I don't know, short?), and the zener got too much current, it mighta failed. if it is the root cause, that is.
(you could pull the zener out of circuit, and if, only IF, there is now no findable supply shorting funnies still going on, put a temporary resistor, same value as the zener series R, to produce a tempy bias voltage. this would show if the rest of the circuit is working, but it relies on the rest of the circuit working.)
FYI here's the values of the components in the audio path schematic aside from the op amps, labelling and use of nearest modern value electro's + supply filtering electro's the values should be the same SW1 is just to switch the 22K script feedback resistor in or out but as I said I'd use the GGG schem for ease of reference
R1 1M R17 150k C1 10n IC1 TL071 Mono Op Amp
R2 10k R18 150k C2 47n IC2 TL074 Quad Op Amp
R3 470k R19 150k C3 47n IC3 TL061 Low Current Mono Op Amp
R4 10k R20 56k C4 47n
R5 22k R21 150k C5 47n Q1 -Q4 2N5952 Matched
R6 10k R22 150k C6 47n Q5 2N4125 General Purpose Silicon PNP
R7 10k R23 3M9 C7 22μ
R8 22k R24 4k7 C8 10n TR1 250k Trim Pot
R9 10k R25 470k C9 10μ SPEED 500k Reverse Log Pot
R10 10k R26 150k C10 47n SW1 SPST
R11 22k R27 22k C11 100μ
R12 10k R28 22k C12 100μ
R13 10k R29 10k C13 10n
R14 22k R30 1M
R15 10k R31 100R D1 5v1 Zener
R16 22k R32 3k3 D2 LED
Quote from: duck_arse on January 23, 2016, 09:04:53 AM
tempy bias voltage
....and whatever you do don't get frustrated and lose your tempy
Great word that duck_arse worthy of much more use I think