Macke Posted March 25, 2022 Report Share Posted March 25, 2022 Hello, I've been doing some searching and digging trying to find another thread with this specific question and was unable to. I just bought an older Brent b that I was told needed a whole new controller (the wheel spins full speed regardless of pedal position) but upon inspection I found a resistor that was fried. Unfortunately it's blackened enough and split in half, so I can't measure resistance and I can't match colors to determine what I should buy. Does anyone have a similar wheel or know of a place I could get a circuit diagram? Amaco/Brent was utterly unhelpful and just told me "we don't know" and "we don't have any circuit diagrams for any wheels". Does anyone else have an old Brent b with the same controller to compare to? Quote Link to comment Share on other sites More sharing options...
Mark C. Posted March 25, 2022 Report Share Posted March 25, 2022 (edited) I think Bill may know rester values-let him chine in I have 2 Brent B wheelsmen is buried and the other is in a box (motor foot pedal control board/switch) everything except a wheel it self . I about it on E bay years ago for parts about $400 any way I went out and shot these photos of the control board -keep in mined they use different folks on this stuff over the years (its all outsourced I'm sure) I included my serial number so you can see what yours is on the outside plate-If I recall that capacitor size may play a big part in this. resistors are sold by the color banding if I recall as well. Also they should be unsolderd to get true values if I recall -Bill will know this stuff well so lets hope he reads this soon as you can see my board has a different capacitor and is really different Edited March 26, 2022 by Mark C. Hulk 1 Quote Link to comment Share on other sites More sharing options...
PeterH Posted March 26, 2022 Report Share Posted March 26, 2022 Might be worth snipping the resistor out and trying to clean it with an abrasive cleaner. PS It's a long time since I read a resistor, quick recap. Resistor Color Code Chart https://tinyurl.com/5n6ud78n A handy tool for reading resistor color code values https://tinyurl.com/5n6ud78n Hulk 1 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 26, 2022 Report Share Posted March 26, 2022 (edited) 19 hours ago, Macke said: but upon inspection I found a resistor that was fried Looks like a snubber around that thyristor so likely low resistance on the order of 10 -100 ohms. So maybe black-brown-black- black or brown-black-black-black. I would try measuring from the core to the lead on each half of the resistor add together and confirm my suspicion. Also when you tip the halves up the color bands may be less distorted underneath and more readable. I am guessing the thyristor is toast as well since this just runs full speed. Also good to just make sure the capacitor is not shorted as well while you are at it.. Might be a good time for a new board or move up in quality to a nice drive from minarik or similar manufacture. Edited March 26, 2022 by Bill Kielb Hulk 1 Quote Link to comment Share on other sites More sharing options...
Macke Posted March 27, 2022 Author Report Share Posted March 27, 2022 Just to follow up on this, I lifted both halves of the resistor today and it VERY much looked like brown-black-black-silver/gold which would indicate 10ohm, so I pilfered a 10 ohm resistor from work today and I'll be installing the board again tomorrow to see what happens. I'm not ready to pay for a new board just yet, but then again the "I'll do it myself" attitude is what got me into pottery in the first place. It was also the much more expensive way to get the bowls and plates that I wanted Will report back at some point tomorrow though! Hulk 1 Quote Link to comment Share on other sites More sharing options...
Mark C. Posted March 27, 2022 Report Share Posted March 27, 2022 Thats great-let us know the outcome Quote Link to comment Share on other sites More sharing options...
Macke Posted March 27, 2022 Author Report Share Posted March 27, 2022 (edited) I meeeean. It did work. Briefly. I haven't properly adjust the potentiometer, which is why I think it was spinning with the pedal all the way back, but the capacitor checked out and so I put it all back together. Got 3-4 slow revolutions out of it before it stopped and started smelling funny. Forgot to put in the magic smoke plug I guess. Back to square one. Ordering a new capacitor because they're fairly cheap, but not sure where I would find a replacement for this thyristor thing. Edited March 27, 2022 by Macke Attached a picture Quote Link to comment Share on other sites More sharing options...
Mark C. Posted March 27, 2022 Report Share Posted March 27, 2022 I would try a 100ohms one next since the 10 ohms fried so fast toadjust the speed take the bottom off foot pedal and adjust the speed control its shows how to in a pinned topic on Brent repairs at top of page on equipment use Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 27, 2022 Report Share Posted March 27, 2022 (edited) This may help http://bitsavers.trailing-edge.com/components/rca/_dataBooks/1975_RCA_Thyristors_Rectifiers.pdf I believei it’s an old RCA triac, page 34 above. You should be able to find substitutes. The snubber circuit is designed to limit the voltage across the SCR or dv/dt if you will. The current is controlled by the resistor but is usually a function of the load inductance or motor in your case. Anyway a blast from the past for me. - google semiconductor cross reference manuals and T4120 B to find a cross reference. This still may not be the entire issue: is the full wave bridge intact at the motor. Did someone change the motor. Simple stuff, but all needs to be checked. I believe You confirmed its value at 10 ohms, so changing this would change the design. You can google how to check a thyristor as well - pretty simple. Edited March 27, 2022 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
Macke Posted March 28, 2022 Author Report Share Posted March 28, 2022 I ordered a new thyristor and a new bridge rectifier, going to be a few days for new components. Will probably look into a new controller if this fails and hope that the new one doesn't blow up immediately after installation Thank you all for your help through this! Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 28, 2022 Report Share Posted March 28, 2022 (edited) 12 hours ago, Macke said: I ordered a new thyristor and a new bridge rectifier, going to be a few days for new components. Will probably look into a new controller if this fails and hope that the new one doesn't blow up immediately after installation One thing clay and electronics have in common - test, test, test. Just a practical note, depending on the cross reference you are receiving the stud on your original thyristor package was isolated. Many configurations will make that stud M2 unless specifically ordered as such. Double check before letting it touch any other circuit or ground when powered else could be an unexpected blast. Edited March 28, 2022 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
Macke Posted March 28, 2022 Author Report Share Posted March 28, 2022 51 minutes ago, Bill Kielb said: One thing clay and electronics have in common - test, test, test. Just a practical note, depending on the cross reference you are receiving the stud on your original thyristor package was isolated. Many configurations will make that stud M2 unless specifically ordered as such. Double check before letting it touch any other circuit or ground when powered else could be an unexpected blast. The replacement I ordered was NTE56022, it also says TO-48 isolated. I'll have to look up how to test em but the NTE cross reference said it was a direct replacement. Looks like almost everything will be here Friday, so I'll update this weekend. All this waiting is giving me plenty of time to get my gardening done at least Bill Kielb 1 Quote Link to comment Share on other sites More sharing options...
Macke Posted April 1, 2022 Author Report Share Posted April 1, 2022 (edited) Ok, so the good news is that nothing exploded, overheated, popped, smoked or otherwise damaged new components. Soldered in a new capacitor, resistor, thyristor and bridge rectifier. The bad news is that the wheel no longer spins - period. Got a late start today and lost the light, but back to more testing tomorrow Not even sure where to start now, but one piece at a time as best I can I suppose. Wish I had more experience with the testing side of things edit: I have my suspicions that the capacitor is bad, I just checked the second capacitor in the pack and didn't get any sort of reading from it, almost like it's not completing the circuit with the multimeter Edited April 1, 2022 by Macke cap check Hulk 1 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted April 1, 2022 Report Share Posted April 1, 2022 (edited) Most multimeters these days will check capacitors. Look for a mfd setting or microfarad. The snubber cap is 0.47 microfarad I believe. If your meter doesn’t have that feature you should be able to see the capacitor charge and discharge by setting the meter to resistance and testing across the capacitor. Your meter will show low resistance and rise to infinity, then switch the test leads positive for negative and your meter will show this rise again as the capacitor charges to the opposite polarity. Each time you switch polarity you will see this rise as the capacitor discharges through the meter and recharges to the opposite polarity. Just changing parts is a difficult troubleshooting method, confirming the bad part or parts first is preferred, hence the test, test, test suggestion prior. Best idea I have is make sure the bridge is not installed backwards, the thyristor terminals match what previously was used, gate, M1 & M2. It’s been fried a few times now so that circuit typically contains a diac to square off the trigger voltage to the gate of the thyristor and a four zener diode bridge to trigger it.. Testing is not hard but you are limited severely by not being able to check for expected voltages around the circuit. Best thought I have would be it used to spin and now does not. One or more of the components you installed is not installed correctly. Hopefully all those installed were not excessively heated when soldering although most of what you installed are fairly robust. Double check all polarities and markings are as they were originally. Camera shots before and after can help. This circuit is likely an old design, hand built and by now I gather there is no fuse protection designed into it else you would be blowing fuses. A commercial drive is so much more robust and precise, quite frankly I am always amazed these wheels were ever popular except they do and have worked for many years for many folks. Edited April 1, 2022 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
Macke Posted April 12, 2022 Author Report Share Posted April 12, 2022 (edited) Ok, been awhile since I've given any update on this. The new capacitor I had installed was good, the resistors all checked good, diodes were ok. With some guidance from a friend I bypassed the PCB and pot/pedal, I also installed a 500w $15 work light in place of the motor to test that the bridge, switch and fuse were good. The light turned on, so I connected the motor in that configuration instead of the light and it ran full speed again (hooray!/?) Now I've narrowed it *back* down to the PCB and pot, so tomorrow when I get home from work I'll run a jumper across the terminals for the potentiometer and see if it gets full current and spins full speed that way. Hopefully it does, then I'll only need to track down a replacement 60 year old slide potentiometer. Worst case scenario, I know how to turn it into a ceramics themed night stand/lamp combo Once I get it figured out I'll try to post a circuit diagram so anyone else that doesn't want to spend the money on a new control board has some sort of reference material Edited April 12, 2022 by Macke Last message Hulk 1 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted April 12, 2022 Report Share Posted April 12, 2022 Any speculation on why the 10 ohm snubber resistor melted? Quote Link to comment Share on other sites More sharing options...
Macke Posted April 12, 2022 Author Report Share Posted April 12, 2022 7 hours ago, Bill Kielb said: Any speculation on why the 10 ohm snubber resistor melted? The yellow capacitor was bad and wasn't providing any capacitance, which is why it fried the new resistor I had put on so quickly. Once I replaced both of those it didn't fry the resistor again, but I think it changed the flow of electricity when the resistor went out and was bypassing the pedal. Reinstalling the components seems to have redirected the flow (correctly) through the pedal again, which is why I assume bad pot, but I'll confirm that tonight. Quote Link to comment Share on other sites More sharing options...
Mark C. Posted April 12, 2022 Report Share Posted April 12, 2022 If you want a cheaper potentiometer check out thge pinned at top of equipment thread page on how to replace a potentiometer (60 year old slide potentiometer. )-its really only 45 years old Quote Link to comment Share on other sites More sharing options...
Macke Posted April 13, 2022 Author Report Share Posted April 13, 2022 I have one of those slide pots waiting to order, but just in case it was one of the trim pots that went bad, with the slide pot being 1Mohm, should I be ordering 1Mohm trim pots too? They don't test well with my multimeter which is why I suspect trim pot issues over slide pot, but since they don't test I can't get a resistance reading in them. Quote Link to comment Share on other sites More sharing options...
Macke Posted April 14, 2022 Author Report Share Posted April 14, 2022 Slide pot works great on its own! I HAD A VARIABLE SPEED WHEEL!! Turns out it doesn't work worth a hoot with the trim pots and I can't get any reading off of them, so I'd say it's safe to assume the trim pots are bad. I pulled them off of the plastic tray (I'm going to see if I can recreate it in a way that would allow for 3D printing a spare). One of the single turn pots has "250K" stamped on it, so I think it might be 250k ohms, but would that mean they're both 250k? Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted April 14, 2022 Report Share Posted April 14, 2022 (edited) Wiat resistance does it Measure between the outside pins? Then what does it measure from the center pin or wiper to each outside pin? It’s got to measure something to one set, if not, move the wiper back and forth and remeasure the wiper to each outside pin. You almost certainly will get a reading from something. Only one side of those pots are used so very unlikely both sides are open. More likely the wiper is dirty and not connecting. Which pot is the high speed pot, the 250k or the unknown? Edited April 14, 2022 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
Macke Posted April 14, 2022 Author Report Share Posted April 14, 2022 https://www.digikey.com/en/products/detail/cts-electrocomponents/201UR105B/98359 This link goes to the blue one (low side) and the part number leads to a 1M ohm 0.2W trimmer The high side is the "250k" one. I tried adjusting the dial on them during measurement and there was no resistance across any of the posts in any position, it's like they're completely shot. The plastic tray definitely smelled like hot/burnt electronics as well. If I had to guess, when the cap went bad it probably took this out with it? Bill Kielb 1 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted April 14, 2022 Report Share Posted April 14, 2022 (edited) I take that all back, if it runs full speed now, you will need to install a 250k pot in the high speed, see how the pedal performs and from there we will be able to determine what the low speed should be. The pedal operates from zero to 1 Meg. If the wheel stops right at the end of pedal travel then the low speed will need to be at least as much as the pedal or more than 1 Meg. Install a 250k in the high speed, make sure it all works and from observation we will be able to pick a good value for the low speed. 250k is very likely not correct for the low speed. Actually without a proper high speed pot, we are pretty sure, but not 100% that it’s fixed till you install one. The low speed can stay out for now until you confirm how it works with a good high speed pot in place. Edited April 14, 2022 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
Macke Posted April 16, 2022 Author Report Share Posted April 16, 2022 (edited) Ordered new trimmers from digikey, they show up between Tuesday and Thursday next week, and I took this afternoon to make a 3D printable version of the plastic tray that they mount to since I had the tray stripped down and could get good measurements off of it. I'll be doing some trimmer assembly once they show up to run a few tests and will share my findings then, as well as the file for the tray once I get confirmation that there's no design issues with the file. I think I'll do my best to do a final write up of the tests I ran through, POSSIBLY a video of the steps taken, and links to components I purchased and replaced. Edited April 16, 2022 by Macke Added info Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted April 16, 2022 Report Share Posted April 16, 2022 10 hours ago, Macke said: Ordered new trimmers from digikey, they show up between Tuesday and Thursday next week, Hmm, what values did you order? Just want to be sure you read the caution above. Quote Link to comment Share on other sites More sharing options...
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