DYI motor controller help for Saia UFR1 AC motor

[myphsto]

OK. Clear now. My question about the DC supply clearly referred to the dc supply of the PA60DX. Have you measured it?

Your oscillograms, assuming they can be trusted, show a very reasonable frequency entering the PA60DX and an entirely unreasonable 120Hz exiting. This can be either a bad measurement, or blown/died out caps of the dc supply. Before going any further i suggest you make sure the dc supply rails actually carry +/-20v or thereabouts.

Apologies on the DC voltage. The input voltage on the PA60DX is AC, same as the supply. The 120Hz scope picture is what is coming off the AC power supply into the board itself not the output of the power amp.
I did remove the motor from this, you can see in one of the board shots. Again my experience is not in AC circuit design, I appreciate the help.
I think my only option is to start replacing caps etc. I contacted someone with the same unit and had them check the power supply and it's coming in at the same voltage and frequency as mine. Ebay provided a replacement PA60DX and still no dice.

 

[myphsto]

For a low voltage 2 phase AC motor an Arduino controlling a STMicro's L6470 (a.k.a "dSPIN") 3A, 8-45V bipolar stepper motor driver should work.
Arduino Nano ~ £1 & L6470 ~£8 on Ebay.
It's intended as a micro-stepping driver for stepper motors.
However, good luck with the repair.

Thanks for the suggestion... I'm getting close to tossing this board in the trash or ordering one of every dang cap and resistor on it and rebuilding it entirely.
I'll take a look at the L6470, I'm Arduino savy so that just might be the ticket.

 

[analog_sa]

The input voltage on the PA60DX is AC, same as the supply. The 120Hz scope picture is what is coming off the AC power supply into the board itself not the output of the power amp.

There is no need to test the input AC voltage with a scope. It is practically never done and the inclusion of this with the other oscillograms is very misleading. On top of that it doesn't appear it is an AC voltage anyway - the 120Hz indicates it is full wave rectified but not smoothed, so smoothing caps must be on board.

Let's try again.

Have you measured, using a DC voltmeter, the supply voltages at the PA60DX supply pins? Between -Vs and +Vs you expect something in the region of 40v dc.

The two input waveforms at the PA60DX inputs (presumably pin1, pin12) look fine, so where are the waveforms at the outputs (pin 5, pin 8)?

 

[analog_sa]

From the photos there appear to be 1ohm resistors in series with the outputs. It is convenient to test the output waveforms at their legs. It is also worth checking with an ohmmeter if one if them has not gone open circuit.

 

[russc]

What is the advantage of using the L6470 vs Arduino pwm outputs alone? Just the integrated drivers, or is there more? Thanks.

Arduino pins are 5V 40ma max.
Also, the L6470 does the hard stuff in firmware - 2 phase sine generation, acceleration, deceleration, current limit.
The Arduino just tells it when to start, stop & what speed.

 

[russc]

You're probably more Arduino savvy than I am but for what it's worth -
When you download the library & start playing
1 - ensure current limit is programmed, default is no current limit. If you are careless when testing an accidental short will destroy the chip.
2 - duty cycle (ie power level) is programmable for both running and acceleration conditions. Default may bizarrely be set lower while accelerating to speed. It puzzled me when my motor wouldn't pick up speed but ran ok once at full speed.

 

[myphsto]

You're probably more Arduino savvy than I am but for what it's worth -
When you download the library & start playing
1 - ensure current limit is programmed, default is no current limit. If you are careless when testing an accidental short will destroy the chip.
2 - duty cycle (ie power level) is programmable for both running and acceleration conditions. Default may bizarrely be set lower while accelerating to speed. It puzzled me when my motor wouldn't pick up speed but ran ok once at full speed.

Thanks, I appreciate the tips. I'm not always the most careful of coders when I start a project I'm sure I would have not set the current limit. I've got an order in with sparkfun so hopefully the saga will be closed soon. At least with this solution I can add some features later on once I'm back in business and calibrated.

I have to give credit to whom-ever designed this board, it's been interesting reverse engineering it. I went from thinking it was junk to appreciating how it was designed to decouple the timing entirely from the AC outlet unlike cheap turntables.