Assuming that the uP is working and your indication that the external display works, that seems probable. Having already replaced the 74HC595, another possibility would be the de-multiplexing N-FETs (Q1..Q4) not turning on and off correctly. So a possible bad FET. I believe that there should be something like a 10k ohm resistor on each FET gate to ground to insure the FET is turned off until the uP actually turns it on. Just my 2 cents worth. -Parris
Can you describe the flicker? The display is multiplexed, so each digit is only on for 1/4th of the time and the refresh rate is 5mS; if the display is moved, it will appear to have a high frequency flicker. Is that what you are experiencing?
Is the display in a socket? Any back connections can cause a intermittent display.
Is the display in a socket? Any back connections can cause a intermittent display.
I pulled the FETs but am short a couple. I'll order some more and give it a try.
If you're not going to use the LED display, you can remove Q1-Q4 and U3 as well as the display.
Your description doesn't help me; can you determine the rate of flicker? Are all the digits flickering? At the same rate? Is the display data correct? Are any digits brighter than others?
If you have a scope, look at each FET gate pin. You should see a 50Hz square wave with a 25% positive duty cycle on each FET. The display data is shifted into U3 and latched every 5mS. The data rotates between LED position 1, then 2-->3-->4--1 etc. Each FET grounds the cathode for the corresponding digit position for 1/4 of the time so in effect, only one LED digit is actually being illuminated at one time, but because the scan rate is 50 times/sec, all digits appear to be on. If the scan rate appears slower than 50Hz and the waveforms on all the gates are correct, then one or more of the FETs are faulty. The gates do not require pull down resistors. The uP pins provide a hard ground to turn them off and an internal pull up when the gates are high. The input impedance of the FETs is extremely high (10's of MOhms); they do present a capacitive element of impedance which can affect their high frequency ability to change states, but at 50Hz it is negligible.
Your description doesn't help me; can you determine the rate of flicker? Are all the digits flickering? At the same rate? Is the display data correct? Are any digits brighter than others?
If you have a scope, look at each FET gate pin. You should see a 50Hz square wave with a 25% positive duty cycle on each FET. The display data is shifted into U3 and latched every 5mS. The data rotates between LED position 1, then 2-->3-->4--1 etc. Each FET grounds the cathode for the corresponding digit position for 1/4 of the time so in effect, only one LED digit is actually being illuminated at one time, but because the scan rate is 50 times/sec, all digits appear to be on. If the scan rate appears slower than 50Hz and the waveforms on all the gates are correct, then one or more of the FETs are faulty. The gates do not require pull down resistors. The uP pins provide a hard ground to turn them off and an internal pull up when the gates are high. The input impedance of the FETs is extremely high (10's of MOhms); they do present a capacitive element of impedance which can affect their high frequency ability to change states, but at 50Hz it is negligible.
Sorry for the weak description. The display seems to flicker at the same rate for all digits. The data on the OLED is correct. The data on the LiteOn display also seems to be correct but difficult to identify because of the flickering. None of the digits seem to be brighter. I will put it on a 'scope later today.
If the FETs are OK, then it has to be something with U3 or the display. You should see random squarewave data on the SDA line (pin 14) in very short bursts (2-5µSec) every 5 mS. You should see 8 evenly spaced clock pulses in very short bursts (2-5µSec) every 5 mS and you should see one positive latch pulse (<1 µSec wide) every 5 mS. The outputs going to the display should be random data, but they should be nearly squarewaves of 5VPP.
Hello
Looking for some help...
I have bought a ready made SG4 alongside a Lenco PTP deck and I'm having some trouble getting it to work properly.
It turns the platter and I can switch speeds however both 33 and 45 are wildly inconsistent.
Could any experienced user or @Pyramid help please?
Thanks, Richard
Looking for some help...
I have bought a ready made SG4 alongside a Lenco PTP deck and I'm having some trouble getting it to work properly.
It turns the platter and I can switch speeds however both 33 and 45 are wildly inconsistent.
Could any experienced user or @Pyramid help please?
Thanks, Richard
When you say the speed is consistent using wall power, are you measuring the speed with the digital tach? If so, and the same tach shows speed variations with the SG4 driving the motor, then the voltage or frequency of the SG4 is varying or perhaps the voltage is too low to begin with (the Lenco uses an induction motor so it is sensitive to voltage as well as frequency). Do you have a way to measure the output voltage and/or frequency? The SG4 is crystal controlled, so the frequency is very stable and I suspect there is a voltage problem.
Can you post pics of the inside of the controller? I have no idea which amp or step up transformer arrangement you are using.
Can you post pics of the inside of the controller? I have no idea which amp or step up transformer arrangement you are using.
Hi, I'll try that next - please bear with me, I'll not get to it today but I'll send pictures as soon as I can... thanks again for the help
