holier grail reverb

[michael_krell]

I have a holier grail reverb that I am trying to get working. I have a feeling what has happened is that the heat from the +5V voltage regulator has fried one of the PCB mounted resistors that is next to it. This resistor is R1 and it directly follows the 12V DC power input. I arrived at this because the input voltage at the +5V regulator is close 2 and 3 when it should be like 7. I know it should be 7 because its gotta be a couple volts higher then the regulators output.

My question is does anyone know what this resistor value is supposed to be so i can replace it and see if it changes anything. I am going to measure the resitance by measuring the current going into the resitsor and the voltage across it. .................

The resitance I calculated is 19.5Volts/10mA =  1.95K

I measured the input current and the voltage across that resitor and since all the input current goes through that resistor, then this must be the value. It doesnt make sense that there should be 19.5 volts across an input power resistor. Please someone let me know what it should be. I have the regulator pulled out so im sure i wont fry any of the digital electronics if i pop one in there.

[michael_krell]

I lowered the value of the resistor which increased the voltage which actually worked. Until i put the regulator in. When i put the regulator I immiately noticed the resistor getting hot. I used a value of Roughly because this brought the voltage down to working level. Besides im pretty sure its just a current limiting resistor anyway.

None of the components are frying which leads me to believe there is a short in the 5V supply after the output of the regulator.

SOmeone please reply and tell me if im in line

[michael_krell]

also something i never mentioned in the last post, when it desoldered the burnt up resistor i found a burn mark in the PBC so i think the resistor burned on its own for whatever reason i need to figure out. IM going to try a new voltage regulator, i already ordered some the other day.

Does anyone know if its common for a voltage regulator to short??

[niftydog]

the heat from the +5V voltage regulator has fried one of the PCB mounted resistors

I would have thought that to be fairly unlikely, however it is possible. The regulators have thermal shutdown, and when they get too hot, they simply turn themselves off. Resistors are pretty hardy devices.

Can you read the bands on the resistor? Have you measured it out of circuit with a mulitmeter?

19.5Volts/10mA = 1.95K

so, there's 19.5V accross the first resistor in the chain, with a 12VDC input. That's impressive! Obviously the 12V supply is unregulated. Obviously this will never work with that kind of voltage drop.

I am going to measure the resitance by measuring the current going into the resitsor and the voltage across it.

but if the resistor is busted, this won't tell you anything useful at all -  Except that the resistor is busted. You've gotta try to read the bands or find a schematic.

[niftydog]

ah, so the resistor is burnt. You need either a schematic, or a friendly forum dweller who's willing to open up their holier grail and read the value for you.

Regulators can go short. If it is a dead short you can measure this with your multimeter also. Otherwise, whip up a test circuit for the regulator or, like you're alluding to, swap it for a known good regulator.

[michael_krell]

Im going to swap in a regulator when I get one and see if that changes anything, If theres a short somewhere I am pretty sure i wont be able to find it

[niftydog]

If theres a short somewhere I am pretty sure i wont be able to find it

while you've got the regulator out of circuit, just measure across each of the three pins. That will tell you if the regulator's short.

[michael_krell]

Yeah theres no short and i get the same problem with another regulator. There also doesnt seem to be a short anywhere because with the reg out i checked the circuit and there was no sign of a short. What value resistor should I put in that it will not heat up. the circuit seems to be drawing about 40 mA which is causing the R1 to heat up very quickly

[niftydog]

well, if it really is 40mA, and a normal 1/4W resistor, you'd want something less than 150 ohms... but I really have no idea so I wouldn't want to advocate doing anything other than replacing it with the original value.

My advice, be patient and wait for some more information before you regret your haste!

[michael_krell]

I admire your wisdom, i will wait

[Mark Hammer]

Is there a heat sink on, or dedicated to, the regulator itself?

[michael_krell]

The regulator is just attached right to the board. I actually just  made a huge discovery. The adapter is supposed to be 18V DC however the voltage coming out is 24 VDC. and it is an electroharmonix adapter that is meant to work with this pedal. I am pretty sure this caused the current limiting resistor to burn up. does this seem probable?

[niftydog]

in all likelyhood the power supply is working perfectly.

An unregulated power supply will put out a voltage much higher than it's rating when it is not under load. Try measuring the voltage again whilst it's connected to a load.

Only a regulated power supply constantly outputs it's exact rated voltage at all times - regardless of whether it's loaded or not.

[michael_krell]

I hear what your saying, but 6 Volts Higher?? that makes no sense. Also the current output is about 2 Amps when the rating on the apdater is 800mA thats more then twice. I would be willing to bet it is the wrong adapter, but i could be wrong. Either way there is a power problem somewhere. I ordered some regulators from mouser so ill try one of those, but i still dont have the proper resistor.

[puretube]

did you buy the stuff 2nd hand?
(the freedom amp wallwart is 18V/1000mA;
the holier grail is 18V/500mA officially...).
someone may have mixed it up;
does it have an E-H sticker on it? - strange -

[michael_krell]

It does have a EHX sticker on it. It is EHX. I emailed them and they told me its normal for the output to be 24 with no load so im taking there word for it. They also told me the Resistor value is 4.7 ohms. I am going to try that out and see what I get but im pretty sure the voltage is going to be too low at the regulator

[niftydog]

I hear what your saying, but 6 Volts Higher??

entirely conceivable and not at all unusual.

Also the current output is about 2 Amps when the rating on the apdater is 800mA thats more then twice.

how did you measure this? Where you monitoring the voltage at the same time?

Even so, a higher current rating makes no difference other than that the voltage will be a bit higher than a lower rated one at the same current draw. You circuit will only draw as much current as it wants, no more, no less... unless it's busted!

[michael_krell]

I understand how current works but i was merely backing up the fact that i thought it was the wrong adapter.

[niftydog]

fair enough, but what I was getting at is that the adapter is not current limited. The rating on the label merely points out that it is designed to deliver the rated current at the rated voltage. It could, therefore, deliver more current at a lower voltage or a higher voltage at a lower current. So when you say;

the current output is about 2 Amps

that is not unusual, but it is only useful information when you know what voltage the supply was outputing at the time you measured 2A current output.

[michael_krell]

ok regardless..... I put in a 4.7ohm resistor which is what its supposed to be (not 4.7k) and the pedal looks like its working fine except i have two problems. The main output does not work and the votlage regulator is getting very hot. I know they are supposed to get hot, but this seems excessive..... probably why the adjacent resistor failed to begin with.