Here is a list of all the postings Les Jones 1 has made in our forums. Click on a thread name to jump to the thread.
|Thread: C0 Lathe Blowing Fuses. Control board short?|
The most likely failure mode for SCRs is anode to cathode short circuit. Looking at at the devices the way they are mounted on the heat sink and with the pins facing down the centre pin is normally the anode and the left hand pin is the cathode. This is the layout for most SCRs in TO200 packages. It would be a good idea to confirm this by looking for the datasheet for the devices used on your board. you can normally find the datasheet using Google or other search engines. Just do a resistance test between anode and cathode with both polarities. Both readings should show over range on your meter. (Or at least a very high resistance.) If they are short circuit you will get a reading of almost zero ohms in both directions.
I suggest that you also check the two TO220 devices which I suspect are SCRs. I think they form a controlled bridge with two of the three diodes. The output of this bridge will feed the motor. The third diode probably powers the control circuit that controls the phase of the trigger pulses to the SCR gates. The small toroidal transformer near the heatsinks will provide isolation between the control circuit and the SCR gates. If one of the SCRs is short circuit and it is not replaced one or both of the diodes that are part of the bridge will be destroyed again when power is re applied.
|Thread: Picador right angle drive|
They are useful for drilling in confined spaces such as drilling up into a studded wall from under the floorboards. I have also use a similar one as part of a setup to cut a helix on my milling machine.
|Thread: Diamond Drills|
If you know someone with a small EDM (Electrical discharge machine.) that would probably work.
Edited By Les Jones 1 on 24/10/2020 11:46:54
|Thread: Using O Rings|
There was an article in issue 156 (Autumn 2009) of MEW on page 15 about using "O" rings. I don't know if that is the one you are looking for.
|Thread: Wiring a Super 7 with a Tyco Crompton Motor|
Edited By Les Jones 1 on 16/10/2020 20:24:40
I too can't see how changing the the NVR switch can effect the problem.
|Thread: Blown band saw circuit.|
We have now confirmed what I suspected in my post on 01/09/20. It has taken 41 days to confirm what would have taken a few seconds if I had been standing next to the band saw.
It will behave slightly differently to the way it was connected in your original diagram, In your original diagram the micro switch was switching the full motor current which was more than it was rated for. It is now only switching the current taken by the coil in the NVR switch. This means that when the cover is open the motor will run while the green button is held pressed. The way it was connected the motor could not be made to run with the cover open.
This is still not the picture I asked for. From the second picture picture in your post at 12:46 on 11/10/20 it looks like the black plastic control box is mounted on the die cast right hand side of the machine and it looks like there is a hole in the hinged left hand cover of the machine that allows access to the red and green buttons, the hole for the key and the indicator light. It looks like the hole in the left hand cover does not go down as far as the plunger on the micro switch. I want to see the INSIDE OF THE LEFT HAND COVER so I can see if there is something on the INSIDE of the cover that presses against the plunger of the micro switch when the LEFT HAND COVER IS CLOSED. This would then explain the purpose of the micro switch.
It is the inside of the panel on the left hand side of the machine that I want the picture of. I think this is hinged at the back of the machine and opens to access the blade and drive rollers.
I have a suspicion that the cover on the left hand side of the machine covers the lower part of the original switch assembly. Am I correct ? Can you post a picture of the INSIDE of this cover showing area around the hole is for the original switch covering about 4 inches around this hole. I think there will be something on the inside of the cover that presses on the micro switch when the cover is closed. This is why I want to see the picture.
It looks like the motor is probably OK. Even if your mutlimeter has an AC current range it will probably be 10 amps maximum and the motor will take more than this when starting. This test was to ensure that the motor did not take a VERY large current that could destroy the new NVR switch. As it did not blow the fuse in the plug it is unlikely to damage the new NVR switch. We now just need to establish the exact purpose of the thing that you called a trip and DeWalt call a micro switch. It is a pity that you have disposed of the original item before we could establish if it was a thermal overload trip or just a NO micro switch.
I agree with Dave's comments. I am not going to draw a wiring diagram for you until we sort out the function of the thing you called a trip and DeWalt call a micro switch. I suspect that the item to the left of the KJD18 (NVR switch) is a emergency stop button. Can you post a picture of the front of the panel that it is on and also the side of this item so we can read the ratings ? (This is so I can decide between wiring it to break the full load or just the feed to the coil on the NVR switch.) Can you also measure the resistance between the connections second new micro switch both with it pressed and with it not pressed ? Can you also post a picture of where this switch is mounted so we can see if it is some kind of safety interlock ?
This is how to connect the motor directly to the mains to confirm that it is not drawing a very high current as I suggested in my post on September 10th. (This is to avoid damaging the new NVR switch if the original fault was caused by the motor.)
|Thread: Inverter Prolem|
Edited By Les Jones 1 on 21/09/2020 18:12:20
|Thread: Problems reading from a 3.5" floppy disc|
As you can read the floppy on your laptop try making a copy onto a new floppy disk. From memory the command at the command line prompt is something like diskcopy A: A:
If the problem is a marginal alignment problem that might just work. Using a head cleaning disk in the suspect drive may also solve the problem.
|Thread: Blown band saw circuit.|
When you receive the second new micro switch test it with your meter BEFORE fitting it to the saw to see if the results are the same as you reported in your post at 12:20 on 01/09/20 for the first new switch. Do you have a way to measure the current taken by the motor ? I expect the running current to be about 5 amps but the starting current will probably be over 20 amps. (It would probable draw the starting current for less than a second.) If you do then I suggest connecting the motor directly to the mains with a fuse in the circuit. (If you are in the UK then the 13 am fuse in a 13 amp plug will serve the purpose.) The reason for this is that I suspect the motor may be drawing too much current which has damaged the NVR or the original trip switch. In one of your posts you said that the resistance across the capacitor terminals was 2.66 ohms. This is actually the resistance of the two motor windings in series. This value seems low for that size motor.
With that micro switch connected as in the diagram in your first post or connected as in the drawing in the manual the motor can't run unless that switch is closed. (For it to be closed it must be pressed from the results of your test in your post at 12:20 on Sept 01.) Can you confirm that your diagram in your first post shows correctly hoe the micro switch is connected ? The KJD22 NVR that you showed in a previous post and the 4 pin version are available from this supplier.
Either version could be used with your band saw. According to the manual versions of your band saw for some countries do not have the micro switch fitted. This is probably to comply with the regulations for different countries.
From your test on the switch that you call a trip switch and DeWalt calls a safety switch it just seems to be a normally open push button switch. The way you show it connected in your first post it must be in the pressed position for the saw to work. Can you post a picture of the original switch that was saw when it failed showing any printing on it. From the description safety switch I am wondering if it could be an interlock switch to ensure the cover is closed for the saw to work. If this switch is intended to be pressed manually is the a label next to it ?
I have now found the manual for this saw here
It includes a schematic but does not seem to be quite the same as I suspected. It does not show the item that Marsh calls a "Trip switch" which he shows directly in series with the input live feed. I had assumed that this was a thermal overload trip switch. The schematic does show a safety micro switch which only breaks the feed to the contactor coil. The manual also shows that there is a safety key which has to be inserted to start the saw. I am now wondering if the thing that Marsh calls a "trip switch" is this safety micro switch.
Marsh, Can you confirm that your saw does NOT have the key that is shown in the manual ? With the "trip switch" not connected can you measure the resistance between it's contacts with it not pressed and also with it pressed.
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