Router repair - speed control board - Router Forums
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post #1 of 29 (permalink) Old 08-27-2011, 02:54 PM Thread Starter
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Default Router repair - speed control board

I have a Trend T4 that only works when switched to max speed (definite 'click' on the speed dial). Soft start is also non-functional.

Investigating the circuit board I found the SCR (BT151) shorted and the gate diode (possible zener) shorted.

Substituted a NTE5558 SCR but cannot identify the diode. I cannot find a schematic for the board (labeled B/230-12/4 110V) and Trend does not reply.

Can anyone help?

Thanks,
Mike
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post #2 of 29 (permalink) Old 08-27-2011, 04:51 PM
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Originally Posted by Relative View Post
I have a Trend T4 that only works when switched to max speed (definite 'click' on the speed dial). Soft start is also non-functional.

Investigating the circuit board I found the SCR (BT151) shorted and the gate diode (possible zener) shorted.

Substituted a NTE5558 SCR but cannot identify the diode. I cannot find a schematic for the board (labeled B/230-12/4 110V) and Trend does not reply.

Can anyone help?

Thanks,
Mike
Hi Mike - Sorry can't help you but I'm interested in case the same thing pops up with my T4. It's just possible that Trend may not even be able to help either. So many companies these days just farm components like a circuit board out with just performance and physical size specs and the design is done outside.
Good Luck

John Schaben

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post #3 of 29 (permalink) Old 08-27-2011, 06:39 PM Thread Starter
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Failure of this board was fairly common at one point and I have hopes that someone with a little more electronic experience has figured out the board and can give us some answers. Otherwise, a replacement board is available, but there are so few components on it, it is easy to replace parts if you know what they are.

Mike
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post #4 of 29 (permalink) Old 08-27-2011, 11:17 PM
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If you can't fix it, just hook it to an external speed control. That won't help with the soft start but the router will be functional at least.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #5 of 29 (permalink) Old 08-28-2011, 08:02 AM
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It may be this one ? 5KP110A 5000W 110V Transient Voltage Suppressor Diode. ? If so ebay 110v diode | eBay

I was in repair for 50 yrs lot's of diode's for different apps. ? It is probly a ziner diode to keep voltage at 110 ?? The band on the diode went to ground ?

del schisler
port st. lucie, florida

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post #6 of 29 (permalink) Old 08-28-2011, 08:45 AM Thread Starter
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This is a very small (about as small as I've ever seen one) blue-colored component about 2x as thick as the wires coming out of it and it has a label of C702 printed on it along with a band at one end. Searching for C702 on the internet hasn't helped one bit.

It is connected to feed the gate of a T151 SCR.

Mike

Last edited by Relative; 08-28-2011 at 09:03 AM.
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post #7 of 29 (permalink) Old 08-28-2011, 09:27 AM
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I messaged Harry to jump in on this one. I think he has one of these routers and is pretty good on electronics.

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post #8 of 29 (permalink) Old 08-28-2011, 09:59 AM
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Quote:
Originally Posted by Relative View Post
This is a very small (about as small as I've ever seen one) blue-colored component about 2x as thick as the wires coming out of it and it has a label of C702 printed on it along with a band at one end. Searching for C702 on the internet hasn't helped one bit.

It is connected to feed the gate of a T151 SCR.

Mike
Hi Mike - A "C" designation on a circuit board is usually indicative of a capacitor. The 702 is probably a numeric reference to a component number on a schematic somewhere. The question then becomes the capacative value and the polarity. I believe the band would indicate the positive (+) terminal. Can you make out any other numbers?
The good news is I believe it is a very common component and should be easily secured once the values are determined.

John Schaben

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post #9 of 29 (permalink) Old 08-28-2011, 10:19 AM
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Quote:
Originally Posted by Relative View Post
I have a Trend T4 that only works when switched to max speed (definite 'click' on the speed dial). Soft start is also non-functional.

Investigating the circuit board I found the SCR (BT151) shorted and the gate diode (possible zener) shorted.

Substituted a NTE5558 SCR but cannot identify the diode. I cannot find a schematic for the board (labeled B/230-12/4 110V) and Trend does not reply.

Can anyone help?

Thanks,
Mike
Hi Mike, I'm not familiar with your router and have only ever repaired one tool speed controller in my scroll saw, BUT, I've repaired numerous touch control light dimmers, I even started such a thread: http://www.routerforums.com/lobby/12...-lamp-etc.html
I don't ever remember seeing such a diode.The original device is a triac whereas you have fitted an SCR, which doesn't contain the internal diode that the triac does for bi-directional firing. Because of the tiny size of the diode, I'd be inclined to try a small signal diode or possibly two in series. Let's face it, there's no way that you can damage the router itself. I hope this is of some help Mike.

Harry



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post #10 of 29 (permalink) Old 08-28-2011, 06:46 PM Thread Starter
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The original device is a triac whereas you have fitted an SCR, which doesn't contain the internal diode that the triac does for bi-directional firing.
I found the tech sheets for both the T151-500R and the NTE5558 and both are called 'passivated SCRs. Main difference (other than manufacturer) is the T151 is 500V and the NTE5558 is rated to 800V and is 6x more expensive.

I also found an application note that shows the T151 in a similar circuit to the T4's circuit and D2 in the 3rd illustration on the PDF page I printed and attached is the little jewel in question. The actual circuit in the T4 is more complicated, but R1, D2, R4 and BT151 seem to be exactly as drawn on the pdf page.

The 'diode' is physically destroyed while taking it out and what I thought was a band on one end isn't really there. I suspect the 702 is the end numbers of the diode but don't have a clue why there is a 'C" in front of it.

Mike
Attached Files
File Type: pdf T151.pdf (14.8 KB, 342 views)
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