A more specific question regarding effects fix - diodes! (1N4003).

ThePrettyDamned

So, I've had a closer look at the main board, and I found 3 faults.  One was a socket unplugged, one was a slightly cracked socket (both could indicate a big knock in the post).  The third is D1, which is located by the 9v input socket and I'm presuming it's to protect from AC or high voltages.  It looks like it has a small crack in it and the wire either side looks to be oxidised - which could indicate it has served its purpose and protected the rest of the 5 boards!

SO

In the schematic (http://www.ibanez.com/parts/2002_PARTS/electronics/tonelok/circuit%20diagram/CF7-01.pdf) the diode D1 is directional and a 1N4003.  

Are there differetn varieties of 1N4003?  Or is one the same as the other?  I ask as I'm going to get one and solder it in.

Also, how would I effectively desolder the old component without burning the rest of the board?  It's quite a tight squeeze (I'll take a photo in a bit).

Cheers for any advice!

frankus

to remove a solder pump or solder braid would be useful - provided it's not smd components - inwhichcase a hair dryer and some conductive glue should suffice   just make sure the iron has been tinned.

I'd imagine the 1n4003 could be replaced by any number of more attainable diodes. I've some 1n4001 if that's confirmed - can post

ThePrettyDamned

frankus said:

to remove a solder pump or solder braid would be useful - provided it's not smd components - inwhichcase a hair dryer and some conductive glue should suffice   just make sure the iron has been tinned.

I'd imagine the 1n4003 could be replaced by any number of more attainable diodes. I've some 1n4001 if that's confirmed - can post

Oh man, that'd be awesome! I'll wait and see, just to make sure it is just for circuit protection and such, but it does look like that's it's purpose.  

Here is a shot of said diode, for reference.  

http://farm4.staticflickr.com/3736/11352743276_622806c577_b.jpg

Which shows the wire is oxidised.  The diode itself looks as if it's split, but I can't get a shot of it.  

ThePrettyDamned

Also, other than that diode, the rest of the pedal looks really well put together - same quality parts as Poodle Pedals would supply, decent, thick PCB's, no SMD components to speak of.  All in all, very impressed for a budget pedal.

The case is *supposedly* plastic, but it feels metal! And looks like it can take serious abuse.

ThePrettyDamned

Just ordered some 1n4003 diodes for the princely sum of a quid.  So I'll just fit one and see what happens! 

I'm just a bit worried about fitting the new one.  Any tips?

ICBM

It's really easy - remove the old one and solder the new one in the same place, the same way round. Cut the old one if it's easier to get it out without damaging the board (the critical part) - snip the leads with a pair of wirecutters if you have a small enough set - the two leads should just fall out of the board when you melt the solder.

The diode is for reverse-polarity protection, so the chances are it's been called into use before and has cooked itself. They more normally short, rather than crack and go open circuit which defeats the protection.

Any 1N400* series diode will work fine, even a 4001 is rated at 50V which is more than it will ever see. If there was physically room to fit an even beefier one, I would - but there isn't.

ThePrettyDamned

Thanks @ICBM

I've got some 4003 on the way, so I should be fine.  It looks burnt! Should I be concerned?

ICBM

No, not if the pedal is working otherwise. It just means that once upon a time it did its job and died to save the rest of the circuit.

Give it an honourable burial .

ThePrettyDamned

Awesome, thanks! Have (another) wisdom.  

Hopefully it'll work once replaced, I'll keep y'all updated.  Hopefully the diodes will arrive in a couple of days (well, you never know...).  

Misterg

ThePrettyDamned said:

Hopefully it'll work once replaced....

If the diode is cracked (and open circuit) it won't stop the pedal working - you've just lost some protection against reverse polarity.

(Which does bring into question what happened to the rest of the circuit in the same event that caused the diode to fail...)

ThePrettyDamned

Dang. That's worrying.

I'll fix the diode, test it then look at the rest of the boards (all of the other 4...).

What components are most likely to cook? Hopefully not the digital chips...

randomhandclaps

Nothing will cook or have cooked with D1 be absent if the pedal is working otherwise.  Most dead diode that have died in battle tend to show no sign of damage so there are probably plenty in pedals serving no purpose anymore.  The only really offer an very short term of protection.  I have however seen a fair few crack diode the where not cracked in the course of duty so it is possible this diode never saw any really action.

It's also worth remembering that this is from Ibanez cheap range of pedals made with cheap labour.  If the pedal works fine otherwise it would not totally shock me to believe that a cracked diode was installed or the diode suffered a physical crack during installation.  As it's only there for protection against something you are unlikely to do how would you ever know?

My belief is that companies do not install reverse polarity diodes to protect their customer as the protection time is quite short.  It's there so if you return a fried pedal they can look and say "You must have used the wrong polarity.".

As both Frankus and ICBM have said the particular diode you use isn't really essential, although you have ordered 1N4003s the only difference between those and the 1N4001s is current handling being 200v as opposed to 50v which would obviously make no difference to you.

 Edit - I though the pedal was working otherwise, but sounds more like the diode gave out and opened up the rest of the circuit to damage.

ICBM

Misterg's point is that if the diode fails open-circuit, the protection is then lost and if the wrong polarity is still applied it will then fry what the diode was protecting. Logically this must be so since the power supply must still be operating up to the point the diode burns out, and so will be afterwards as well. You can only hope that it cracked and went open-circuit as it cooled down after the power was turned off, rather than in the process.

I've recently seen a couple of pedals where this did not happen, because of the use of very high-current power supplies... resulting in totally fried pedals that were beyond economic repair. If the pedal is currently not working, chances are that happened.

ThePrettyDamned

ICBM;104476" said:

Misterg's point is that if the diode fails open-circuit, the protection is then lost and if the wrong polarity is still applied it will then fry what the diode was protecting. Logically this must be so since the power supply must still be operating up to the point the diode burns out, and so will be afterwards as well. You can only hope that it cracked and went open-circuit as it cooled down after the power was turned off, rather than in the process.



I've recently seen a couple of pedals where this did not happen, because of the use of very high-current power supplies... resulting in totally fried pedals that were beyond economic repair. If the pedal is currently not working, chances are that happened.

Well, that's a massive shame.

I'll keep it in a bin for spare parts I guess!

ICBM

I also agree with randomhandclaps that the protection given by the diode - assuming a fairly capable power supply which won't either blow or shut down with a short on it - is limited, and that the function might be more to show up misuse.

Really, instead of *shorting* the power supply by being in parallel with it, the protection diode should *block* it by being in series - but this means getting slightly less voltage to the circuit, so ideally you then need a slightly higher voltage supply. The old Boss pedals which took an ACA (12V) adaptor were like this, with a diode and a resistor in series with the power jack. (Although this is defeated if you daisy-chain multiple pedals, so be careful.)

ThePrettyDamned

Cool.  Well, it's been informative, at least.  I'll keep it for spare bits, so if any other pedals screw up, I have a mini box of resistors and caps to nab

It was a freebie thrown into a deal for a Nova Repeater.  Which, by the way, if fecking brilliant! I'm being lame and staying on dotted 8th so far, but the tape and analogue modes are awesome.  When I have another bandit (:D) I'll run it in stereo and use ping pong. AWESOMEBALLZ.

Misterg

I'm not sure how much time/effort you want to put into it, but it might be worth checking a few voltages around the circuit:

Check you've got 9V at pin 8 of IC1 IC2 & IC3 ; 4.5V at the junction of R3 & R4; and +5V coming out of IC7.

If these voltages are OK, you can check whether IC1 / 2 / 3  are functional by checking the voltages on each group of 3 pins that is one op-amp are all at the same voltage (i.e 1,2 &3 should be the same voltage, as should 5,6 &7) - probably about 4.5V.

If there is no 5V supply, it might be worth taking a punt on changing IC7 (Maplin N69CA  should be a drop-in replacement but they rob you blind for them - 99p!). A 79L05 would probably work for testing on a PSU.

That's probably as far as I would go.

If the supply has been reversed and there are any tantalum caps in the circuit (like little beads, rather than cans or boxes) they will likely be shorted - they *really* don't like reverse voltage that 'normal' electrolytics usually survive. The chips won't like a reversed supply voltage, either.