MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

Here are the resistors in question, R628 & R629. I believe it is a
four digit part number, every other resistor on the board is (i.e.
10R0 or 2001...), no three digit part numbers. Any clues?
Thanks, Steve

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

Sorry, I should have been more specific. They blew because the fets
failed. The entire post is in s.e.r., I'm just trying to figure out
the values of the resistors now.
Steve

On Sat, 5 Apr 2008 14:21:02 -0700, "BobW"
wrote:



"Steve" wrote in message
.. .
Here are the resistors in question, R628 & R629. I believe it is a
four digit part number, every other resistor on the board is (i.e.
10R0 or 2001...), no three digit part numbers. Any clues?
Thanks, Steve

Steve,

They got too hot.

Bob

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

On Sat, 05 Apr 2008 21:34:50 -0700, Hattori Hanzo
wrote:

On Sat, 5 Apr 2008 20:52:00 -0700, "BobW"
wrote:



"Hattori Hanzo" wrote in message
. ..
On Sat, 05 Apr 2008 16:31:54 -0500, Steve wrote:

Sorry, I should have been more specific. They blew because the fets
failed. The entire post is in s.e.r., I'm just trying to figure out
the values of the resistors now.
Steve

On Sat, 5 Apr 2008 14:21:02 -0700, "BobW"
wrote:



"Steve" wrote in message
om...
Here are the resistors in question, R628 & R629. I believe it is a
four digit part number, every other resistor on the board is (i.e.
10R0 or 2001...), no three digit part numbers. Any clues?
Thanks, Steve

Steve,

They got too hot.

Bob



Well, from left to right, I see the numerals:

4 - blank - 5

So, being only three digits, it is likely a 5% part.

With the 5 as the multiplier, it will be 4x00,000.

Where the x is the missing digit.

How would you burn up a 4megohm resistor?

Be afraid...be VERY afraid.

Bob


Well, they are 1/16th Watt SMDs right? They look like 0805 or 1206.

So it had to be an HV spike that went through it. A spike that was
higher in voltage than the rated voltage of the part.

You can bet that once the breech occurred, the resistance of the part
was considerably lower... for at least a millisecond...

Now, it appears certain that they would read "open".

I've looked at gate resistors for fets in similar amps, & the others
in s.e.r agree, this is probably a low value part, so the part number
would be 4XR5, making it 40 something ohms. The fets popped, which
caused these resistors to blow.

Thanks for the help,
Steve

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

On Sun, 06 Apr 2008 10:44:30 -0500, Steve wrote:


I've looked at gate resistors for fets in similar amps, & the others
in s.e.r agree, this is probably a low value part, so the part number
would be 4XR5, making it 40 something ohms. The fets popped, which
caused these resistors to blow.

---
Since 5% (E24 series) parts don't have three significant digits in
their values and 4R5 isn't a valid 5% value, these should be 1% (E96
series) resistors if the legend is, in fact, 4XR5.

Furthermore, for any value starting with 4 and ending in 5, the only
possible value for X is 7.

http://www.logwell.com/tech/componen...or_values.html

JF

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

On Sun, 06 Apr 2008 14:53:36 -0500, John Fields
wrote:

On Sun, 06 Apr 2008 10:44:30 -0500, Steve wrote:


I've looked at gate resistors for fets in similar amps, & the others
in s.e.r agree, this is probably a low value part, so the part number
would be 4XR5, making it 40 something ohms. The fets popped, which
caused these resistors to blow.

---
Since 5% (E24 series) parts don't have three significant digits in
their values and 4R5 isn't a valid 5% value, these should be 1% (E96
series) resistors if the legend is, in fact, 4XR5.

Furthermore, for any value starting with 4 and ending in 5, the only
possible value for X is 7.

http://www.logwell.com/tech/componen...or_values.html

---
If the legending isn't 4XR5, but 4X5, then it should be a 475 ohm 1%
resistor.

JF

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

On Sun, 06 Apr 2008 15:08:40 -0700, Hattori Hanzo
wrote:

On Sun, 06 Apr 2008 14:53:36 -0500, John Fields
wrote:

On Sun, 06 Apr 2008 10:44:30 -0500, Steve wrote:


I've looked at gate resistors for fets in similar amps, & the others
in s.e.r agree, this is probably a low value part, so the part number
would be 4XR5, making it 40 something ohms. The fets popped, which
caused these resistors to blow.

---
Since 5% (E24 series) parts don't have three significant digits in
their values and 4R5 isn't a valid 5% value, these should be 1% (E96
series) resistors if the legend is, in fact, 4XR5.

Furthermore, for any value starting with 4 and ending in 5, the only
possible value for X is 7.

http://www.logwell.com/tech/componen...or_values.html

JF


Very likely true (perhaps), however, I must note that especially for
very low value resistors, a company will make any value part a customer
needs or specifies, and it does not have to be one from any of the
standard schedules.

Granted, the appearance would likely differ, and the likelihood of those
being custom value parts is low. It is possible, however.

It could also be a 4R75 value as well.

---
True; good catch.
---

The 4XR5 value you declared is not a valid number as the R designator
for the decimal is always just after the first significant digit.

---
That's not true. It appears where the decimal point would appear and,
in the 47.5 ohm case would read "47R5".
---

A 47R5 is easily expressed in normal methodology by 4751, which is how
it would appear for a 1% part.

---
That's also incorrect.

The first three digits are used to describe the numerical value of the
resistance and the last digit is used to indicate the number of zeroes
which follow.

The example you've given, therefore, would have a resistance of 475
followed by one zero, which would be 4750 ohms.

A 475 ohm resistor would be imprinted with "4750" indicating that
there were zero zeroes following the three significant figures.

Thus, "4752" would indicate a resistance of 47500 ohms, "4753" would
indicate a resistance of 475000 ohms, and so on...
---

The R designator is for values that cannot be derived by way of a
multiplier and significant digit expression. Values below 10 Ohms, IIRC.

---
In the E96 series there's no way of using a decimal multiplier to
indicate a resistance of less than 100 ohms, so your recollection is
faulty.
---

So, "The legend is, in fact,..." is incorrect as there are NO 1% E96
values that get expressed that way.

---
OK, then, how would you use three significant figures and a decimal
multiplier to describe a 97.6 ohm resistor?

JF

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

On Sun, 06 Apr 2008 15:09:49 -0700, Hattori Hanzo
wrote:

On Sun, 06 Apr 2008 14:56:28 -0500, John Fields
wrote:

On Sun, 06 Apr 2008 14:53:36 -0500, John Fields
wrote:

On Sun, 06 Apr 2008 10:44:30 -0500, Steve wrote:


I've looked at gate resistors for fets in similar amps, & the others
in s.e.r agree, this is probably a low value part, so the part number
would be 4XR5, making it 40 something ohms. The fets popped, which
caused these resistors to blow.

---
Since 5% (E24 series) parts don't have three significant digits in
their values and 4R5 isn't a valid 5% value, these should be 1% (E96
series) resistors if the legend is, in fact, 4XR5.

Furthermore, for any value starting with 4 and ending in 5, the only
possible value for X is 7.

http://www.logwell.com/tech/componen...or_values.html

---
If the legending isn't 4XR5, but 4X5, then it should be a 475 ohm 1%
resistor.

JF

That is the only valid 5% schedule part to match it. Unless it is a
custom part, I'd say that that is the correct valuation.

---
Don't you mean 1% schedule part?

JF

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

On Sun, 06 Apr 2008 13:15:04 -0700, Hattori Hanzo
wrote:


Sorry, I should have been more specific. They blew because the fets
failed. The entire post is in s.e.r., I'm just trying to figure out
the values of the resistors now.

Not that this can guarantee anything, but every other resistor in this
unit has four digits. I'm willing to bet it's 47.5 ohms, but I could
of course be wrong.

Thanks for all the posts,
Steve

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

On Sun, 06 Apr 2008 16:38:41 -0700, ChairmanOfTheBored
wrote:

On Sun, 06 Apr 2008 17:56:52 -0500, John Fields
wrote:

On Sun, 06 Apr 2008 15:09:49 -0700, Hattori Hanzo
wrote:

On Sun, 06 Apr 2008 14:56:28 -0500, John Fields
wrote:

On Sun, 06 Apr 2008 14:53:36 -0500, John Fields
wrote:

On Sun, 06 Apr 2008 10:44:30 -0500, Steve wrote:


I've looked at gate resistors for fets in similar amps, & the others
in s.e.r agree, this is probably a low value part, so the part number
would be 4XR5, making it 40 something ohms. The fets popped, which
caused these resistors to blow.

---
Since 5% (E24 series) parts don't have three significant digits in
their values and 4R5 isn't a valid 5% value, these should be 1% (E96
series) resistors if the legend is, in fact, 4XR5.

Furthermore, for any value starting with 4 and ending in 5, the only
possible value for X is 7.

http://www.logwell.com/tech/componen...or_values.html

---
If the legending isn't 4XR5, but 4X5, then it should be a 475 ohm 1%
resistor.

JF

That is the only valid 5% schedule part to match it. Unless it is a
custom part, I'd say that that is the correct valuation.

---
Don't you mean 1% schedule part?

JF

Not with only three digits in the value expression.

---
Point is (unless it's a 4.7 megohm resistor) '475' can't describe a
valid E24 series part.

OTOH, since the middle digit's gone, it could be something like a
Panasonic ERJXXQX4R7X.

http://www.panasonic.com/industrial/...AOA0000CE3.pdf

JF

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

Hattori Hanzo wrote:

One cannot express a 1% part value with only 3 digits.

You certainly can if it's an E24 value.

Graham

MTX 6500D Blown Resistors - resistors.jpg (0/1)
 

On Sun, 06 Apr 2008 20:34:58 -0500, Steve wrote:

On Sun, 06 Apr 2008 13:15:04 -0700, Hattori Hanzo
wrote:


Sorry, I should have been more specific. They blew because the fets
failed. The entire post is in s.e.r., I'm just trying to figure out
the values of the resistors now.

Not that this can guarantee anything, but every other resistor in this
unit has four digits. I'm willing to bet it's 47.5 ohms, but I could
of course be wrong.

Thanks for all the posts,
Steve

Just got an email from MTX, they are indeed 47.5 ohms.

Thanks to everyone for the help!

Steve