Orac spindle drive problem

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Orac spindle drive problem

Post by Ridgeback » Sun 01 Nov , 2015 15:16 pm

Hi All,
Having read many of the blogs on your forum pages relating to Orac spindle drive issues, I am sure you are going to be thinking, oh no not another one!! I am afraid it is true, yes another one. I have recently acquired an Orac which was running fine when I viewed it and collected it but is not so now. I had a busy period of about five weeks where I was unable to get to it, but when I finally did I excitedly input a program, simulated it and then went to run it. It ran well for about three quarters of the program and then the spindle began to play up, slowing right down to a crawl, but still turning. I ran it again but this time it did not pick up speed at all.
I tried running the spindle in manual mode and this was just the same. Whilst running I placed my hand on the chuck to discover that there was no torque at all, I was able to stop it quite easily.
I am no electronics wiz kid but have still been prepared to have a go at trying ascertain the problem. Most replies on the forum seem to suggest that the 10v zener diode on the PC1951 board is the cause of the problem. I did not have a 10v reading on this board so concluded this to be the source of my problem. New diode bought and replaced in the board and hey presto, no change at all, spindle still crawls round with no torque and no 10v reading either.
Where to next?
This is, I hope, where your vast experience will come to my rescue.
Cheers Colin.

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Re: Orac spindle drive problem

Post by MAX THE MILLER » Sun 01 Nov , 2015 19:01 pm

I'm not an expert where Orac electronics are concerned, but I do have an electronics background.

If the zener is functioning correctly you should be able to measure 10 VDC across it. If this is not the case, then assuming the diode is not short-circuit, which seems unlikely as it's a replacement, you'll need to look at where the zener gets its supply from which will be from a higher voltage source. Unless the current drawn from the 10V supply is very low, it won't be derived directly from the zener. Instead the zener will control a power transistor and the 10V supply will come from there.

Is a circuit diagram for the PC1951 board available?

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Re: Orac spindle drive problem

Post by Ridgeback » Sun 01 Nov , 2015 22:16 pm

Hi Max,

Thanks for your response. Being new to this forum, I am feeling my way in so don't be alarmed if I pig up a little here and there.

I found this link on this forum under Orac and the two drawings found on Pages 18 and 19 are the ones which relate to the 10v zener diode line. The actual drawing number PC 1951 is NOT the one in the bottom right hand corner of the actual drawing, but it is hidden within the drawing TITLE box. Took me a while to work it out!! I hope I have directed you to the source of the drawings correctly.

Orac-1985-Book-1-GSM-Syntel-Electrical-Drawings.pdf

I have had a look at some of the other wiring drawings shown in this book and I find it quite hard to work out the connection between one board and the next. This makes it difficult to track what voltage should be incoming to the PC 1951 board. I hope it is more clear to you.

Cheers Colin.

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Re: Orac spindle drive problem

Post by MAX THE MILLER » Mon 02 Nov , 2015 11:01 am

I have located the drawing. I'll have to work out how it interfaces with the other circuit boards.

It would be useful to check the power supply voltages on the board with a meter.

Between terminals 2 and 3 of Terminal Block 1.

Between terminals 2 and 1 of TB1.

Between terminal 2 of TB1 and the output of the 7805 voltage regulator, where it connects to the 4K7 resistor. Expect to see 5 volts here.

Of course that may not be as easy as it sounds if the terminal aren't accessible.
Attachments
spindle.jpg
spindle.jpg (223.12 KiB) Viewed 5062 times

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Re: Orac spindle drive problem

Post by MAX THE MILLER » Mon 02 Nov , 2015 11:37 am

I've traced the power wiring back to the regulator board. The two supplies are +12V and -12V.

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Re: Orac spindle drive problem

Post by Ridgeback » Mon 02 Nov , 2015 20:08 pm

Hi Max,
These are the results I found using a standard analogue multi-meter. Where –ve voltages were present I had to reverse the connections to ascertain a reading.

Between Terminals 2&3 on TB1. +ve lead on T2 & -ve lead on T3 = +12 volts.
Between Terminals 2&1 on TB1. +ve lead on T1 & -ve lead on T2 = +12 volts.
Between Terminals 2 on TB1. & Output line of 7805 regulator. -ve lead on T2 & +ve lead on 7805 regulator output = +5.2 volts.
This last figure sound like it is a little high at +0.2 volts as I believe the 05 suffix of the 7805 indicates 5.0 volts. Perhaps it just might be a poor quality multi-meter?
Could this small increase be a cause for concern? I have no idea what effect this will have on the rest of the circuitry.
Judging by the connection reversal I assume the two 12volt results are good news as this would make one -ve 12 volts and the other +ve 12 volts.

Something occurred to me when doing the last lot of tests. Whenever I power up the machine for the first time, it will kick out the MCB in my consumer unit on that line. I reset it (the MCB) and then power up a second time and each time I go through this sequence it holds in on the second attempt only. Very odd!!

What will be the next step?

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Re: Orac spindle drive problem

Post by MAX THE MILLER » Mon 02 Nov , 2015 21:11 pm

Your voltage reading are fine and you've proved that the board has all the necessary power supplies. 5.2V from the 7805 is OK, it's the fact that it's stable that counts.

I haven't worked out all the inputs to the board, but the outputs all go to the Spindle Speed Controller board which I believe has the designation M2125. Unfortunately I can't find a circuit for M2125, but I haven't looked too hard so far. The only connections to M2125 are mains in, three wires designated A, B and C which go to the spindle motor and four wires from the spindle control board PC1951.

At the PC1951 end there's a pair of a pair of relay contacts which are connected to Terminal Block 2 terminals 3 and 4. When the relay on PC1951 is operated these contacts extend a "loop" into M2125. Unfortunately I have no idea what the loop does. Perhaps it just turns on the motor. You may be able to check that the contacts are closing by measuring the voltage across TB2/3 and TB2/4. If there is a voltage it should drop to zero when the relay operates. This may occur when the motor starts. This might be a high AC voltage, so start with your meter on the highest AC range and work down.

The other two terminals TB2/1 and TB2/2 should, I believe, carry a variable voltage which depends on the motor speed selected. The zener will limit this to 10V.

Do you see a voltage across TB2/1 and TB2/2 when the motor is running and does it vary with the speed selected?

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Re: Orac spindle drive problem

Post by Ridgeback » Mon 02 Nov , 2015 22:27 pm

Hi Max,
Thanks so far. It is a bit late to go out to my garage to do the next suggested checks so I have spent some time indoors looking up what I though I had remembered seeing some time ago. I eventually found this to do with the Brown Pestell Controller and have attached it for you to look at. I hope it is of some help.
I did see the wiring diagram M2125 listed in one of the Denford Administrator Posts but it looks like it was not included in the Post on this site.

Cheers Colin.
Attachments
Brown Pestel (1).pdf
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Re: Orac spindle drive problem

Post by MAX THE MILLER » Tue 03 Nov , 2015 9:12 am

That's the diagram alright. I couldn't make head nor tail of it though, until I realised it's missing all the odd pages! I get the gist of it though.

The relay on PC1951 does control the start and stop of the motor, so as long as you can start and stop the motor using M commands it's probably OK.

Best concentrate on what conditions you're seeing on TB2/1 and TB2/2.

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Re: Orac spindle drive problem

Post by Ridgeback » Wed 04 Nov , 2015 0:17 am

Hi Max,
Running a bit late today as I had two small jobs to do on my trusty old Boxford lathe.

Well spotted with the odd page number missing issue. I hadn’t noticed that.

I put the meter across the L&N lines on the Brown Pestell Controller terminals and there is 250V ac there. I also tried across the terminals marked A,B&C, expecting either 250V ac or 380V ac between the motor connections but only got a dismal flicker on the meter as the motor barely turned round.

Looking at Diagram M2050 (Wiring Interconnections) I put the meter across the N line Mains incoming and T6 of the Toroidal Transformer and again got 250V ac. Was not sure where to check results from T1 through T5 of this Transformer though.

On PC1951 I put meter across TB2/3 and TB2/4 and got reading of 16V ac when the spindle was OFF. As you predicted, this dropped to 0V when I turned the spindle ON. When I say spindle ON, I mean barely turning as usual and I cannot increase the speed with the manual controls. There is no voltage at all at TB2/1 and TB2/2. I could physically see the small relay on this board kicking in and out as I turned the motor ON and OFF.

Using Diagram S2108, I also checked for voltage between TB2/1 and the junction of diode 1n4007 and the 1K resistor, No voltage. I then tried again, on the other side of said 1K resistor and TB2/1 and still nothing. I assume there should be something coming out of terminal 6 of the LF356 component which is the next connection to the 1K resistor?

I think I have left you with enough to think about. Your help is much appreciated.
Colin.

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Re: Orac spindle drive problem

Post by MAX THE MILLER » Wed 04 Nov , 2015 11:07 am

Here's how the circuit works:-

A 6840 programmable timer on TI0.C module (S2044) generates a waveform, the characteristics of which vary with the spindle speed selected. The waveform turns a BC377 transistor on the same board on and off.

The output of the BC377 alternately lights and extinguishes a Light Emitting Diode within the opto-Isolator on the Spindle Control Unit PC1951. The LED is optically coupled to a photo transistor within the opto isolator. The output of this photo transistor turns the ZTX107 transistor on and off. The ZTX107 connects and disconnects +5V from the 7805 to one of the inputs of the LF356 operational amplifier. The other input to the op-amp is fed by a voltage set by a 10K pot wired across the -12V and +12V rails. The output voltage of the op-amp depends on the difference between the two input voltages and is fed to the Spindle Speed Controller M215. The 1N4007 diode stops the output voltage going negative and the 10V zener limits it to a max of 10V.

Fault finding on PC1951 is most easily done using an oscilloscope, But it may be possible to deduce some things from meter readings.

Check whether you get a voltage between TB1/4 and TB1/5. With any luck this should change with the motor speed selected and the needle may pulse when slow speeds are selected. I cannot be certain of this though. If the frequency is high the meter's needle may be unable to respond.

Use TB1/2 as a reference point for taking the following voltage readings.

Check what voltage you get at the collector of the ZTX107 (junction with the 1K5 resistor. This voltage should follow the voltage at the input to the opto isolator.

Do the same at pin 3 of the op amp which is one of its inputs.

Check the voltage at pin 2 of the op amp which is its other input. The 10K potentiometer sets the voltage here which should be fixed.

Check for a voltage at pin 6 the output of the op amp.

Disconnecting one of the wires TB1/4 or TB1/5 will extinguish the LED and lock the circuit in one state, which may produce a voltage at the output of the op amp on pin 6.

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Re: Orac spindle drive problem

Post by Ridgeback » Wed 04 Nov , 2015 19:52 pm

Hi Max,

WOW, this is getting deep. I have a prior engagement tonight so will only be able to attempt the above checks tomorrow. I am not sure what I checked a couple of days ago, but due to the extremely slow running of the motor I did get a reading which caused pulsing of the meter needle. Will have to see if I can locate it again.

Cheers Colin.

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Re: Orac spindle drive problem

Post by Ridgeback » Fri 06 Nov , 2015 0:29 am

Hi Max,

Not too sure about what conclusions I have come to, but here are the results to the test I carried out this evening.

TB1/4 and TB1/5 with motor running (approximately 10 RPM) and my meter set on 2.5 V dc, NO movement at all.

TB/2 as reference: ( Black lead of meter here).

At collector of ZTX107, motor ON or OFF, 0V dc.

At Pin 3 of OP Amp, motor ON or OFF, 0V dc.

At Pin 2 of OP Amp, motor ON or OFF, 0V dc.

At Pin 6 of OP Amp, 12V +ve dc. (my meter re-set to 50 V dc).

Now as I write this up I realise I have made a mistake with your last request. You said disconnect ONE wire from either TB1/4 or TB1/5 and I disconnected them both. Damn!!! The results I got however, were the same as at Pin 6 previously, 12V +ve dc.

I did venture a bit further whilst I was there and checked at the terminals from the spindle speed sensor (Drawing No S2120 for PC1852 or PC1853) which connect to (Drawing No S2106) PC1965, (but on the drawings S1714, I downloaded, this seems to have been up dated to PC1690). I shall continue, (Drawing No S1714), bottom right hand corner of the Board, first four terminals in are the connections from the spindle speed sensor. Beginning on the right and working to the left, I get +5V between T1 and T2. I also get +5V between T3 and T4. If I run the motor I get a flashing LED just above T2 (ish) and the meter reads a pulsing voltage around +3.5V across T3 and T4. Not sure exactly what this means though, but wondered if the flashing indicated that the optical sensors are working fine?

Remembering all the time that the motor is running at about 10 RPM and I cannot manually increase or decrease this speed on the front manual control panel. I am also unable to manually jog the X and Z axis at this time even though the beeper beeps when pressed!!!

Max, I will be out of touch for the coming week as I have a prior engagement where I will be in Spain from 7/11 to 13/11 inclusive. I will however be able to read a reply to this post, tomorrow, if you manage to find time to reply. Thanks again for your time and patience with me. I am learning so much about the inside this machine which I never thought I would when I bought it. Can’t wait to begin making things though.

Cheers Colin.

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Re: Orac spindle drive problem

Post by MAX THE MILLER » Fri 06 Nov , 2015 10:46 am

There's a lot for me to think about there. Your break in Spain will give me a bit of breathing space.

Following a cursory glance at your readings I've a couple of comments.

1. You mention using TB/2 as reference. It's obviously a typo, but I hope you meant TB1/2 (Terminal block 1, terminal 2).

2. You say you have +12V on pin 6 of the op amp ie the output. That being the case you should also read a voltage on the other side of the 1k resistor connected to pin 6 of the op amp (Junction of 1k and 1N4007) and also on the other side of the diode where it connects to TB2/2. The last reading will be clamped to 10V by the zener diode.

Possibilities are;-

1k resistor open circuit.
1N4007 open circuit.
Zener diode short circuit or connected the wrong way round.
TB2/1 and TB2/2 being short circuited by something on the spindle speed controller.

Disconnecting the wire from TB2/2 would remove any possibility of the spindle controller short circuiting the output. If there's still no voltage on TB2/2, measure the voltage across the 1k resistor (one meter lead on each side of it). If you see a voltage here the zener is the problem.

I'll check whether my Triac PC uses the PC1951 board. If so I'll take some readings for comparison.
Last edited by MAX THE MILLER on Mon 16 Nov , 2015 11:59 am, edited 1 time in total.

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Re: Orac spindle drive problem

Post by Ridgeback » Fri 06 Nov , 2015 15:59 pm

Hi Max,

Thanks for that. As I said, I will not be able to go ahead and do any checking as I need to pack kit ready to go.

Your first point, it was a typo, I meant TB1/2.

Your explanations from point 2 onward seem pretty obvious now as I read them. I didn't think to continue checking further down the line. All things to do when I get back.

Thanks,
Colin.

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Re: Orac spindle drive problem

Post by Ridgeback » Sun 15 Nov , 2015 22:26 pm

Hi Max,

Back from my trip and ready to go again, or so I thought.

I had doubts about my checking of the Op-amp results as I did not fully understand the configuration of the 8 pins. A bit of research showed this to be true so I went back to double check my results. I had nothing from Pin 6 of the op-amp so ventured further back in the circuit. I got +5v from 7805 which was good. Then something happened, not sure what, but I must have accidentally touched something I should not have because I got a buzz in my hand and when I re-checked the 7805 there was nothing. A quick check of the fuses showed I had blown BOTH 0.5A fuses on the S2074 board and only had one spare fuse. I have more on order as I type this so there will be a little delay while I wait for them to arrive. I will start checking again once they arrive. I hope to be able to give you more reliable info then.

I looked up the LF356 op-Amp, just in case this was the problem child and found that they were slightly different to the one I have on my board. I have the tin can style with tab and 8 wires out the bottom but those I found advertised are the "8 legged BUG style" chips!!! Will this be a problem if this is found to be the problem?

Cheers Colin.

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Re: Orac spindle drive problem

Post by MAX THE MILLER » Mon 16 Nov , 2015 11:37 am

LF356's in round metal cans, as opposed to plastic Dual In Line (DIL) packages are available on UK ebay and from Farnell. You'll probably find that the actual device on your board has a suffix such as A, H or BH.

Rather than probe the LF356 directly, with a risk of shorting its leads, it would be better to probe the leads of resistors etc which are connected to the LF356.

22k resistor is coloured red, red, orange. (Pin 3)
33k orange, orange, orange. (pin2)
1k brown, black, red. (pin 6).

What is the S2074 board?

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Re: Orac spindle drive problem

Post by MAX THE MILLER » Mon 16 Nov , 2015 14:23 pm

What is the S2074 board?
I see it's the board with the + and - 12VDC supplies. Make sure these are present on the PC1951 before you start measuring other things or you'll be chasing your tail.

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Re: Orac spindle drive problem

Post by Ridgeback » Tue 17 Nov , 2015 23:38 pm

Hi Max,

The 0.5A fuses arrived, are in place and this is what I found.

Between Terminals 2&3 on TB1. +ve lead on T2 & -ve lead on T3 = +12 volts.
Between Terminals 2&1 on TB1. +ve lead on T1 & -ve lead on T2 = +12 volts.
Between Terminals 2 on TB1. & Output line of 7805 regulator. -ve lead on T2 & +ve lead on 7805 regulator output = +5.2 volts.
All the same as I had achieved previously, but this time I am a little more certain of the results.

I got 0V between TB1/2 and both T2 and T3 of the LF356.
I got 2.6V between TB1/2 and the junction between 33K resistor and the 10K variable resistor.

At this point I found it hard to trace the circuit as I was working on both sides of the PC1951 board. I have gone to great lengths to superimpose the actual components onto the printed circuit diagrams (on paper of coarse) so I can see everything from one side of the board which is where I hope to check from. I hope this will make checking easier and less chance of shorting, as you suggested.

I have the chuck turning once again, albeit very slowly as usual. When rotating it by hand I have also noticed that the LED's on the right hand side of the PC1965 board flicker on and off. One, many times per revolution and the other, only once per revolution. My understanding of this is that the optical reader is doing its job.

As it is late now, I will leave you with this info, will return to a more thorough check on Thurs evening and get the results off to you after that.

Cheers Colin.

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Re: Orac spindle drive problem

Post by Ridgeback » Thu 19 Nov , 2015 23:09 pm

Hi Max,
My plan to make checking easier has worked. I now have a set of results which I think are more useable than before.

I used TB1/2 as my checking (Datum point) for all the locations on the circuit board I wanted to check and below are the results I found. I used a digital multi-meter.

7805 input (TB1/1) +11.93V
7805 output +4.94V
Junction of 4K7 resistor and 1K resistor +1.48V
Junction of ZTX107 and 1K resistor +0.75V
Junction of 1K5 resistor, 22K resistor and ZTX107 +0.018V
Junction of 22K resistor, 22K resistor and 0.1uF Cap +0.018V
Junction of 22K resistor, 0.1uF Cap and LF356/T3 +0.018V
Junction of 33K resistor and 10K variable resistor +2.44V
Junction of 33K resistor, 0.1uF Cap and LF356/T2 +0.016V
Junction of 10uF 16V Cap and LF356/T4 -11.90V
Junction of 1K resistor, 1.0 & 0.1uF Caps and LF356/T6 -0.145V
Junction of 1K resistor and 1N4007 diode -0.145V
Junction of 1N4007 diode and 10V Zener Diode 0.0V
I also checked across TB1/4 and TB1/5 +0.53V

Looking at the results, which were so clear now, I noticed a massive volts drop across the 1K5 resistor. I placed the digital multi-meter on either end of this resistor and read 4.92V (polarity determined by which way round the leads were placed).

I noticed a smaller volts drop across the 33K resistor. I placed the digital multi-meter on either end of this resistor and read 2.42V (polarity determined by which way round the leads were placed).

I also noticed a smaller volts drop across the 4K7 resistor. I placed the digital multi-meter on either end of this resistor and read 3.46V (polarity determined by which way round the leads were placed).

Can it be assumed that these three resistors are not functioning correctly and might need replacing?

I hope I have given you information which is not confusing and is helpful enough to move things along.

Cheers Colin.

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