Identification of a resistor

[Tony Cape]

I posted a pic, I'm working on a Graflex/Singer model 1015 projector pre amp board and it has no sound. I found the fuse blown, so I tried substituting another fuse of what I thought was the same(1.5a at 25v) and I think the resistor started to smoke, so I shut it down. I'm pretty sure I have a bad rectifier, but I'm trying to positively identify the resistor too.

Looks like Brown-Red-silver-silver.

I looked at the schematic for it and it looks like a 2w .47 ohm resistor.( my copy isn't very clear to read) also plus or minus 5%
If I look up that resistor, it looks nothing like the picture. Any ideas?

Thanks for any direction

 

[toddalin]

"Brown" look orange or yellow to me.

 

[petehall347]

0.47 is yellow violet silver

 

[Tony Cape]

"Brown" look orange or yellow to me.

I believe you are right, it looks like orange when I look at some of the other small resistors on that board.
So looking at the colors, what is the resistance?
Here is a pic of the diagram

 

[petehall347]

yellow violet silver gold 0.47 5%

 

[cademan]

Let's have some pics. The resistor is smoking because of a short somewhere. Usually it is a shorted output device that tends to fry resistors.

Please don't guess (shotgun). Grab a simple volt/ohm meter and do some basic troubleshooting.

 

[Tony Cape]

Ok, I'm getting somewhere, I determined by looking at another 2w 5% 47 ohm resistor on the same board and measuring resistance on it, the first band on this unknown one is a gold band, then silver?, red, and orange?, That seems like.32 ohms

 

[Tony Cape]

ok, my supper just arrived, be right back

 

[petehall347]

what resistance does it measure ?

 

[petehall347]

it is orange red silver for 0.32 ohms .

 

[cademan]

EDIT: R28 of the schematic. If the rectifier diodes were bad, it wouldn't smoke as it would not be getting any power.

I think I would still check the outputs.

 

[Tony Cape]

what resistance does it measure ?

it measures 1.6 ohms

Also, and I verified this, the resistor is connected to one side of the output of the rectifier(FB100 or NTE166) and the other end of the resistor is connected to the positive side of 2 800mfd capacitors. There is also an output transistor tied to that same side. According to the troubleshooting section it says "fuse blows immediately", replace shorted diode D1(rectifier) and check output transistor TR-8, TR-9 and also check D-7, maybe to see if they fried too?

I'm just trying to identify the parts I may need at this point and the resistor just looked weird, could not match it to colors corresponding to schematic identification of that resistor.

 

[petehall347]

If that resistor really is the ohms you have stated, it sure looks to be an emitter resistor which usually comes off of the emitter pin of an output transistor.

So yeah, check them outputs!

looks like a current limiter on the positive supply to me . also known as a slow fuse . well thats what i call them .something is shorted beyond it . possibly the filter capacitor if lucky . need to see more schematics .

 

[cademan]

looks like a current limiter on the positive supply to me . also known as a slow fuse . well thats what i call them .something is shorted beyond it . possibly the filter capacitor if lucky . need to see more schematics .

Yeah I went back and did some editing of my post after actually looking at the schematic. Lol.

OP, is R28 the one that started smoking? I only ask as it doesn't look smoked, just cracked.

 

[petehall347]

need to see what that supply feeds to comment more . i can only guess a seized motor or something .saying that the cap isnt right for motors .

 

[cademan]

D1 is a bridge rectifier and is very simple to diagnose a short using a meter set on the ohms scale. After that, check the recommended outputs.

I also am not getting anything from those colors or its my eyesite but I would say that if you are getting a reading on that resistor and its not smoking or burnt, leave it alone for now and look for the fuse blowing culprits.

 

[Tony Cape]

I'm fairly certain I have a bad bridge rectifier. I did the following test with my fluke 87 set on diode: black lead on - of dc output, red lead on one, then the other AC input, I get a reading, I also get a reading when I put the red lead on - of dc output and the black lead on either of the AC inputs. Then if I put the black lead on the + dc output and the red lead on either of the AC inputs I get a reading and if I then put the red lead on the + of the dc input and the black lead of either of the AC inputs I get a reading,the readings were about 1.6 volts.

 

[petehall347]

fault is after the rectifier . assuming AC apply is to the right of it with the fuses .

 

[Tony Cape]

fault is after the rectifier . assuming AC apply is to the right of it with the fuses .

So you are telling me the bridge rectifier is ok? based on what I posted?- I thought it was supposed to conduct in one direction but not the other. I just tested in the same way a brand new 25 amp 50v full wave rectifier and it conducts in one direction when tested like I did above, except the voltage is about .48 volts.

It's 26 volts AC, then one leg thru the fuse(which was blown when I started this nightmare) and onto one of the AC inputs of the bridge rectifier.
Unless you are saying something past the rectifier fried it.

 

[petehall347]

yes it should only conduct one way .that is depending on which pins you have your meter on .
if it was bad i would suspect it to be shorted from ac to dc pins .