Resistor Substitution Rules (Neotec S600)

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The monitor model probably doesn't matter, this question is more general than that... But alas...

I'm replacing resistors on a Neotec S600 that decided to nuke a decent amount of parts.

The resistors I'm replacing are listed in the schematic/parts list as 1W 4.7 OHM MOF RESISTOR. Easy enough. I order a few new 1W 4.7 OHM resistors, and the new ones are significantly smaller than the old ones. This has me concerned that I did something wrong in ordering the replacement resistors.

What are the rules on substitution of styles of resistor? If I guess a resistor style wrong (wirewound vs film), are there long-term consequences? Also, I think I read that the color of the resistor casing usually doesn't matter.

Pictures:

The first picture shows the new resistors compared to the one I removed. The resistor had discolored and severely distorted its color bands.

NeotecResistors2.jpg


This second picture shows a comparison between two resistors on the board (both are being replaced).

NeotecResistors1.jpg


Thanks.
-Todd
 
The monitor model probably doesn't matter, this question is more general than that... But alas...

I'm replacing resistors on a Neotec S600 that decided to nuke a decent amount of parts.

The resistors I'm replacing are listed in the schematic/parts list as 1W 4.7 OHM MOF RESISTOR. Easy enough. I order a few new 1W 4.7 OHM resistors, and the new ones are significantly smaller than the old ones. This has me concerned that I did something wrong in ordering the replacement resistors.

What are the rules on substitution of styles of resistor? If I guess a resistor style wrong (wirewound vs film), are there long-term consequences? Also, I think I read that the color of the resistor casing usually doesn't matter.

Pictures:

The first picture shows the new resistors compared to the one I removed. The resistor had discolored and severely distorted its color bands.

NeotecResistors2.jpg


This second picture shows a comparison between two resistors on the board (both are being replaced).

NeotecResistors1.jpg


Thanks.
-Todd

I just guess which resistor you were talking about,R425
before i seen the picture..
Resistors don't open up them self..for no reason.

Theres a short on that line,,why are you going to replace it..if theres a short
on that line..get the board out and start measuring the components on that line.
i already know what you should say.
don't forget to measure after lifting one leg.. Get the schematic out and check it.
you need to clear all shorts before powering up again..
You can see another bad part in the picture!!!!!
 
To answer the other part of your question.

Wirewound resistors can add inductance to the circuit, metal film doesn't. Metal film doesn't typically have large wattage values so I am not sure if they make them bigger than 2 or 3 watts. (never looked)

Typically having a higher wattage resistor with the same value ohms as a substitute for the original is ok. But your correct to question the makeup of the resistor in this case. But you will need to understand the circuit in order to tell if the inductance from the wirewound resistor will affect it.
 
To add a bit to this conversation.
Yes, you can buy metal film resistors in larger sizes. 2 & 3W is available but not real common.

The resistors in the original post -- looks like the purchased ones were the "small form factor" variety. For example - a 1 watt small form factor resistor will be about the same size as a regular 1/2 watt resistor. Although they rate it at 1 watt... in my opinion, due to reduced size and heat dissipation abilities, I consider it a glorified half watt resistor. Look for 'small form factor" in the description. If it says that then go with one size bigger to get the same heat dissipation.

I'll do this sort of thing with Williams supplies. It calls for a 2W 39K resistor... which is what fits. To replace it, I use a 3W 39K small form factor resistor which typically costs about the same as a 2W regular. Not sure it really gains much but, in that location, every little bit helps.

There... clear as mud?

Ed
 
First, thanks for the replies guys. I appreciate the assistance.

Yep, Ohmerone, you are right. I neglected to mention in my original post, but I've replaced a substantial amount of parts that were testing "out of spec". I saw a dead short on a BY359X diode. The TDA4861 was also showing very odd readings, so I swapped it out to be sure. I've replaced a large number of capacitors in the region that were also out of spec (and some severely destroyed, see picture below). There was even one that had completely ceased to exist, just the legs and some fuzz left behind. So, yes, there are a bunch of reasons the resistors destroyed themselves. I'm hoping all of those reasons have been corrected at this point and am trying to restore these resistors to working.

So if I'm reading what you are saying correctly, I should replace them with wirewound as the originals are likely wirewound (due to their larger size?). The ones I got are obviously Metal Film.

That said, do the colors of the bodies of the resistors mean anything? One of the replacements I received is a wirewound, meets the same spec, but has a blue (almost looks painted) body instead of the standard ceramic-looking brown that the original was. I know some of them are flame-proof, and the new one is a tighter tolerance than the original.

For these 4.7 Ohm resistors, the parts list shows them as MOF, which is metal oxide film. So that would be non-wirewound *AND* different than the Metal Film I ordered. Anyway, the one I ordered was http://www.mouser.com/ProductDetail/Vishay/PR01000104708JR500/?qs=3M67XevNmDLNpXGccBvCkg== . Again, I'm concerned due to the size difference with the replacement compared to the originals. It seems I should re-order 1 Watt Metal Oxide Film 4.7 Ohm resistors. According to what I've read, the Metal Oxide handle heat better than Metal Film (which is quite apparently critical in this circuit).

NeotecCapAsplode.jpg
 
First, thanks for the replies guys. I appreciate the assistance.

Yep, Ohmerone, you are right. I neglected to mention in my original post, but I've replaced a substantial amount of parts that were testing "out of spec". I saw a dead short on a BY359X diode. The TDA4861 was also showing very odd readings, so I swapped it out to be sure. I've replaced a large number of capacitors in the region that were also out of spec (and some severely destroyed, see picture below). There was even one that had completely ceased to exist, just the legs and some fuzz left behind. So, yes, there are a bunch of reasons the resistors destroyed themselves. I'm hoping all of those reasons have been corrected at this point and am trying to restore these resistors to working.

So if I'm reading what you are saying correctly, I should replace them with wirewound as the originals are likely wirewound (due to their larger size?). The ones I got are obviously Metal Film.

That said, do the colors of the bodies of the resistors mean anything? One of the replacements I received is a wirewound, meets the same spec, but has a blue (almost looks painted) body instead of the standard ceramic-looking brown that the original was. I know some of them are flame-proof, and the new one is a tighter tolerance than the original.

For these 4.7 Ohm resistors, the parts list shows them as MOF, which is metal oxide film. So that would be non-wirewound *AND* different than the Metal Film I ordered. Anyway, the one I ordered was ... . Again, I'm concerned due to the size difference with the replacement compared to the originals. It seems I should re-order 1 Watt Metal Oxide Film 4.7 Ohm resistors. According to what I've read, the Metal Oxide handle heat better than Metal Film (which is quite apparently critical in this circuit).

The ones you bought definitely are the small form factor version. The data sheet shows the 1W resistor being 8.5mm long max. A standard 1/2 watt resistor is about 10mm long. I would go with standard size resistors instead of small form factor - the more surface area you can get, the better.

Color does say small form factor versus regular size. BUT - each and every manufacturer has different color codes for these so it's pretty much useless. Some use pink, some use blue. Real smooth finish is what I usually see on a metal film. Rough finish is often seen on metal oxide. This, too, varies widely amongst manufacturers.

I would go with the same size and type as the original... or even go a size bigger in wattage if you can find them as the mounting method would appear to allow it.

Ed
 
First, thanks for the replies guys. I appreciate the assistance.

Yep, Ohmerone, you are right. I neglected to mention in my original post, but I've replaced a substantial amount of parts that were testing "out of spec". I saw a dead short on a BY359X diode. The TDA4861 was also showing very odd readings, so I swapped it out to be sure. I've replaced a large number of capacitors in the region that were also out of spec (and some severely destroyed, see picture below). There was even one that had completely ceased to exist, just the legs and some fuzz left behind. So, yes, there are a bunch of reasons the resistors destroyed themselves. I'm hoping all of those reasons have been corrected at this point and am trying to restore these resistors to working.


NeotecCapAsplode.jpg

From my experience with this circuit you
Need to check or replace R424,R429,R427.
D403 nd D404 for short
Q401,q402,q403 short,or leaky
C416 22/160
If bad
Need to replace all at the same time before powering up, for best result's
Need to also check if the powersupply voltages are all running to high.
 
First, thanks for the replies guys. I appreciate the assistance.

Yep, Ohmerone, you are right. I neglected to mention in my original post, but I've replaced a substantial amount of parts that were testing "out of spec". I saw a dead short on a BY359X diode. The TDA4861 was also showing very odd readings, so I swapped it out to be sure. I've replaced a large number of capacitors in the region that were also out of spec (and some severely destroyed, see picture below). There was even one that had completely ceased to exist, just the legs and some fuzz left behind. So, yes, there are a bunch of reasons the resistors destroyed themselves. I'm hoping all of those reasons have been corrected at this point and am trying to restore these resistors to working.

So if I'm reading what you are saying correctly, I should replace them with wirewound as the originals are likely wirewound (due to their larger size?). The ones I got are obviously Metal Film.

That said, do the colors of the bodies of the resistors mean anything? One of the replacements I received is a wirewound, meets the same spec, but has a blue (almost looks painted) body instead of the standard ceramic-looking brown that the original was. I know some of them are flame-proof, and the new one is a tighter tolerance than the original.

For these 4.7 Ohm resistors, the parts list shows them as MOF, which is metal oxide film. So that would be non-wirewound *AND* different than the Metal Film I ordered. Anyway, the one I ordered was http://www.mouser.com/ProductDetail/Vishay/PR01000104708JR500/?qs=3M67XevNmDLNpXGccBvCkg== . Again, I'm concerned due to the size difference with the replacement compared to the originals. It seems I should re-order 1 Watt Metal Oxide Film 4.7 Ohm resistors. According to what I've read, the Metal Oxide handle heat better than Metal Film (which is quite apparently critical in this circuit).

NeotecCapAsplode.jpg


Did you get all the parts in to repair the monitor?
Did you see R424 was damaged you can see in picture part of the
body of resistor is missing..part of the band is missing..
should be open, the resistor next to r425.
Let us know what you find..
 
Thanks for the additional information. I'm ordering parts now. Here's what I've come up with, let me know if you see anything awry.

R424 47 1/2 watt
R429 24k (24?) 5 watt cement (schematic lists as 24k ohm in one spot, 24 ohm in another) I don't have my chassis here to verify.
R427 10 1/2 watt
D403 1n4148
D404 uf202g subbed egp20d
Q401 2sc945p subbed KSC945CGBU (C is center collector, G is 200-400 hFE as-per original)
q402 2sa733
q403 irf9630
C416 22/160

Thanks yet again for the assistance, sorry for the delay in my reply.
 
Sorry for the gigantic delay on this one. Finally got back to working on this beastie.

Here's where I'm currently at (details below). The monitor is still showing no sign of life, yet I can't find anything else wrong with it. That said, nothing is any MORE wrong with it than there was before. It's also not killing the new parts I put in (whew!).

I've replaced all visibly damaged or burnt resistors. (R425, R301 and one other I don't have its position on-hand). I've repeatedly tested all caps for ESR and replaced quite a few that were marginal, questionable, or obviously bad/blown. I've paid close attention to parallel caps for false ESR testing.

I've been over the board with a fine toothed comb, but here are some highlights...

D407 - BY359X diode (was dead short, replaced)
D403 - Tests OK
D404 - Tests OK
R424 - Tests OK
R427 - Tests OK
R429 - Tests OK
Q401 - Tests OK
Q402 - Tests OK
Q403 - IRF9630 - Was dead short, replaced.
C416 - Tests OK
Q414 - Tests OK
Q413 - Tests OK
C312 - Tests OK
C313 - Tests OK
U301 - TDA4861 - Odd readings compared to new part, even out of circuit. Replaced along with the unknown resistor position I mentioned above.

I've also concentrated on the other silicon items on the board (transistors and the like), and am no longer finding anything obviously bad at this point.

I've also tested the fuse. It's good. :)

The monitor is doing nothing on application of power. No clicks, no noise, no lights, no sirens, nothing at all. Just dead like it's not even plugged in. This leads me to believe it has to be something really stupid or really obvious.

I am at the point where I think it'd be beneficial to isolate and test the power supply... However, I'm not quite sure how to achieve that on this monitor. (Edit: I think I see it now. Looks like R138?) For some reason, I'm not seeing it when I look over the schematic (nor have I seen it in my Googling). Any pointers would be appreciated.

By the way, Ohmerone... You are helping me on three monitor threads simultaneously... LOL. THANK YOU for the help. :)
 
Last edited:
Power Surge?

R138 is not used..and on the schematic..showing NC
@ C1 on schematic that i have..

It might be a good time to quit and send it out for repair??
Your parts list is alot longer then mine..Like C416 with the hole in it..

But if you like we can go further and t/s the SMPS Next?
do you have the polarity on the ac plug correct if wrong
the smps won't start..
Was there a power surge..was the game board damaged too?
 
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