This board is for moving the backstop on our 1982 Challenge 37" hydraulic cutter. The backstop still moves forward and backward, but it's extremely slow moving forward. The schematic say the toasted resistor at bottom right is an 8KΩ. I'm assuming the other two are 1K. The length of all three is approximately 8.5mm.
QUESTIONS
1. Because of it's size, would that mean it is a 0.5W?
2. The Arc Suppressors are QUENCHARC 504M02QA47. Is there a way to test them with a basic multimeter?
3. I'm guessing the "black components" are capacitors. All I can read off them are "WEP", "170" and what looks like a "W" logo (Wiltronics?).
How can I determine what they are and test them to see if they are good?

Not that it helps any, but the other components I've been able to identify are:
RY4V-U 120V relay
Vishay VS-16RIA60 SCRs
The TRIAC is labeled "GE SC1600 8552"
Not shown but connected to the board:
OHMITE 2Ω 55W F503 8631
DALE .5Ω 55W HL-55-09Z Y8513

Needless to say, this board is no longer available (EOL was 2005) and I've only found one place that claims to repair such. They want $250 to "maybe fix it" and another $250 to simply replace everything. Before I go that route, I figured I could just replace the components that test bad, starting with the 8K resistor.

Any assistance would be greatly appreciated.

 

The schematic say the toasted resistor at bottom right is an 8KΩ.

I'd like to see that schematic if possible. The resistor unlikely failed on its own but instead was turned into a fuse by failure of one of those big rectifiers (I'm assuming that's what they are.) Go over the board with your multimeter and check if the diodes are functioning, and see if that resistor has failed "open". There are limits to what you can learn in-circuit but it's a place to start. I don't think that's a 1/2-W by the way, it looks more like 1/4W or 1/8W. There's no problem about going with one with a higher rating, though.

 

Hi,
1. Seems like that. Anyway, you can use a 1W resistors, there's a lot of free space on the PCB
2. 504M02QA47 . It seems, it's a 0,5uF capacitor in series with 47 Ohm resistor. You can apply 120VAC on the suppressor and read the current . It should be 23mA roughly
3. Photo of those capacitors needed

 

The TRIAC is most probably an SC160D.

The size and shape of the burnt resistor when compared to the small DO-1 diodes indicates this resistor is indeed 1/8W. As others have said, chances are it wouldn't have blown unless something else was faulty. This resistor is in series with what looks like a diode (black component with a white band on one side) and it controls the gate of one of the SCRs. If the SCR or the diode became faulty, I imagine that a higher current draw would have developed and burnt the weaker component - the resistor in this case.

You mentioned you have the schematics, so you would know better the arrangement. The SCRs seem to be connected in anti-parallel, with its Anode and Cathode connected against each other, with their gates connected to the diode/resistor/relay. Those would determine the polarity of the motor, thus the "forward" SCR is probably connected to the burnt resistor. The TRIAC is connected in series to this SCR arrangement and its gate is connected via another resistor to the relay. That would probably be the ON/OFF component.

Good luck with your repair!

 

In old age the high temperature resistor materials wasnt invented jet. Therfore wattage may guess by the area - d=2 mm L=9 mm means 0.08W, d=2 and L=13 mm means 0.125W, d=4 L=13 means 0.25W however some green type have d=6 L=18 as well 0.25W. Red type d=5 L=16 may expect 0.5 W. Formfactor d=8 L-15 You may lead to the 1 W, but d=10 and L=18 rather obey the 2W.

 

I'd like to see that schematic if possible.

 

The length of all three is approximately 8.5mm.

That would make them 0.5W (1W if they're the not-as-common miniature style).

From Yaego:

 

THANKS for all the information! I understand and agree that it's very likely that the failure of something else cause the resistor to fail. So, it looks like I'll be replacing several components.

MORE QUESTIONS
1. One of the arc suppressors has a little brown area on the cover of one of the leads. I assume it has overheated. Unable to easily find any QUENCHARC 504M02QA47 .5w/47Ω/.5µF arc suppressors. Is there an equivalent or something else I can replace it with?
2. According to WEP, the silicone rectifier diodes (I thought they were capacitors) are 2.5A 1000 PIV. Would a Vishay RGP25M- E3/54 be an equivalent?
3. Since the cost is about the same, would it be better to use metal oxide film resistors versus carbon film resistors?

I've located the SCRs and a TRIAC. If I can find an equivalent to the arc suppressors, I can replace EVERYTHING for around $50. Much better than the $250/$500 the repair place would charge.
View attachment Cutter Backgage.jpg

 

You mentioned you have the schematics, so you would know better the arrangement. The SCRs seem to be connected in anti-parallel, with its Anode and Cathode connected against each other, with their gates connected to the diode/resistor/relay.

Good luck with your repair!

Uhhhhh... okay. I've attached the schematic in hopes that you could help me determine what likely needs to be replaced. Probably because I don't really know what I'm looking at.

When just measuring resistance, I get readings from the resistor, diode, arc suppressor and SCR on what I'm guessing is the Reverse circuit. On the Forward circuit, I only get a reading on the SCR, but it's not the same as the other SCR. Don't know if it's because the resistor, diode and possibly the arc suppressor have failed on that circuit or the SCR itself is damaged as well.

I can easily find the 8K resistor, the diode, the SCR and even the TRIAC. I CANNOT find an equivalent to the QUENCHARC 504M02QA47 .5w/47Ω/.5µF arc suppressor. What might I find one and what would be an acceptable substitute?

 

QUENCHARC 504M02QA47 .5w/47Ω/.5µF .
A thick film or a wirewound resistor of 47 Ohm +/-20 % , 0.5-1W , in series with a 0.47uF +/-20 % 250VAC or 630VDC capacitor is a suitable substitute for the arc suppressor

 

Thanks, Pryex! Mouser had all the parts except that specific arc suppressor and the TRIAC. They do have an arc suppressor that fits within your suggested specs and I was able to find an unused TRIAC on eBay. Now the "fun" begins.

I GREATLY APPRECIATE ALL OF Y'ALL'S HELP AND INFORMATION!