Tunerview II LCD Not Working

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Tunerview II LCD Not Working

ddd4114 Fri Dec 21, 2012 1:50 am

Hi,

I've owned a Tunerview II for about 4 years, and until recently, it has worked flawlessly. A few weeks ago, I noticed that the (blue) LCD screen would randomly flicker, and the white text would dim to the point where the characters were hard to read. This problem occurred off and on for about 2 weeks, and then it began flickering all the time. Eventually, the display would dim so much that it would completely stop working. One of these times, I noticed that "Connecting..." was briefly displayed on the screen, which tells me the entire unit is losing power, not just the screen. As of a few days ago, the screen will not illuminate at all.

To diagnose the problem, I removed the Tunerview from my car and wired it to a separate 5V supply. The LCD screen still will not illuminate. At this time, the Tunerview pulls 2.5 mA, which is obviously not enough to do anything useful. I also confirmed that the connector on the cable in my car is receiving a steady 5V from the ECU. The RX and TX pins are also active.

While connected to the 5V supply, I did some probing and found that while the voltage drop across the connector terminals is 4.99V, VCC on the main board is only receiving 4.3V with respect to GND. I'm not sure if this is a normal voltage loss from the FTDI chip or if there is a loose connection. I also noticed that the LCD screen pins 2 and 4 are only receiving 2.8V with respect to GND. The ATMega chip is also only receiving 3.5V.

I then connected a laptop to it via USB, and it worked perfectly again. While it ran, I saw that the voltage between VCC and GND dropped to 4.0V, but the LCD pins 2 and 4 were now receiving 4.3V. The ATMega chip was receiving about 3.8V.

Finally, I disconnected the USB cable and again tried to power the device by my 5V supply. The screen now illuminates, but it flickers constantly.

At first glance, there seems to be no bad solder joints or broken wires. The transistor on R1 appears to be fine.

Has anybody had a problem like this before?

Thanks,

Dan

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HRTuning Fri Dec 21, 2012 2:59 am

It sounds like a possible backlight issue. You should be seeing the LCD operate even if the backlight does not if that's the case. I'm not sure what I can do to help.

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ddd4114 Wed Dec 26, 2012 5:48 pm

I know you're not going to be wild about this idea, but a circuit diagram would really help to diagnose it. Knowing how the supply voltage is distributed through the circuit would help a lot.

I poked around more today, and I couldn't figure anything out. The problem is intermittent, so it's hard to troubleshoot. The only thing that's repeatable is that powering it via USB always works. I've tried powering the display with the other two connectors, and the top one seems to work too. Routing 5V through either of the bottom two connectors results in a flickering display.

If I can't figure out the issue, would you consider taking this one as a core and replacing it at a discounted rate?

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HRTuning Wed Dec 26, 2012 6:30 pm

The top port is direct, as it's actually an output for peripheral devices, not an input. The two bottom ports use the two diodes next to them. The top diode is for USB power. It then flows to the power plane. Power should never be below ~4.8v. What is the measurement on the two sides of the diodes (Depending which way you're powering it).

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ddd4114 Thu Dec 27, 2012 10:05 pm

The voltage downstream of the diodes with respect to GND is always ~4.3 V. The voltage drop across them is ~0.72 V, which is normal.

I noticed that whenever the display flickers, the supply voltage to the ATMega chip drops to 1-1.5V suddenly and then returns to normal. At first I thought I didn't have the probe solidly on the pin, but it seems to happen all the time. However, VCC is unaffected by the flickering and always stays at ~4.3V.

I also hooked it up to an adjustable power supply when it was working, and there doesn't seem to be a voltage that causes it to flake out. I went from 4V to 5.3V, and it never flickered. The backlight got very dim (as expected), but it was stable. 4V supply (3.3V after the diode) was still enough to keep the ATMega running too.

I also tried hitting the diodes and capacitors with a freezing spray, but that had no effect on the LCD display.

It's tough to diagnose because it happens so randomly and I can't figure out any pattern to it.

Any ideas?

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HRTuning Fri Dec 28, 2012 12:04 am

None of that makes any sense. The voltage drop for those diodes is not .72 and the Atmega should be seeing the same voltage as everything else. It does not operate at 1.5v.

5.3 is too much. If you've done that you've damaged the system. It's a 5v system max.

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ddd4114 Fri Dec 28, 2012 6:40 am

What is the voltage drop supposed to be? ~0.7V is very common for diodes, but of course it depends on what type you use. I ASSumed you used something cheap and common.

I also don't understand why the ATMega isn't receiving the same voltage as VCC. It's definitely flaking out because the voltage is dropping that low, but I can't figure out why.

5.3V should be perfectly fine. The absolute maximum voltage rating for both the ATmega644P and FT232RL chips is 6V, and I only exposed them to ~4.5V (after the voltage drop across the diode). I don't know what type of LCD display you use, but it should be able to handle 4.5V just fine if it's designed to run on a 5V supply voltage before that diode. I can't think of any other components on that board that shouldn't be able to handle 5.3V, let alone 4.5V.

Whatever the case, up until this point, I have always powered the device via the ECU, it worked fine in that exact setup for about 4 years, and then it suddenly started flaking out, so it's not like this problem was a result of any of my probing around this week.

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HRTuning Fri Dec 28, 2012 2:21 pm

.7 is normal.

Sorry. I thought I read 5.3 after the diode.

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ddd4114 Fri Dec 28, 2012 4:49 pm

Do you have any ideas for other things to check?

What are your thoughts about taking this one as a core?

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HRTuning Fri Dec 28, 2012 4:50 pm

Nope.

As a discount on a replacement is fine. Use email.

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ddd4114 Tue Jun 11, 2013 11:09 am

This was resolved by HRTuning back in December.

EDIT: Oh, you're a spammer. Now your post makes a little more sense.

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TunerView II

 

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