LCD blank


Wayne Robertson
 

Hello, I have the QCX-mini, Rev 2.  Upon powering up, the LCD illuminates but no adjusting of R47 results in a display other than the black rectangles.  Page five of the Troubleshooting Manual, 4th paragraph says "Check with a DVM that there are no short-circuits between adjacent LCD pins, or between any LCD pin and Gnd or Vcc. Check for continuity between each LCD pin and the corresponding pin on the processor. You can do this with the board upside down, and the LCD module plugged in."

I have no shorts between pins but pin 1 does short to ground.  The schematic, best I can tell, actually shows pin 1 wired to ground so, is this a problem or not?

And, I gather from reading posts that Vcc is a 5v source.  Where do I find Vcc to continue my tests?

Thanks all!

--Wayne, K4WK


 

Wayne, do you get one row of black rectangles or or two? It makes a big difference to the next steps.

When you say Pin 1, do you mean pin 1 of the connector? Ground on that point would be good, along with pin 4.

Vcc starts off at the regulator, front left of the main board as you look at it from the operating perspective: BNC on the right, controls up. If you have a Rev 2 board, it's the rightmost pin on the regulator - opposite side to the diode.

--
Julian, N4JO.


Wayne Robertson
 

Thank you Julian for your quick reply.  I have two rows of rectangles when R47 is entirely counterclockwise. 

By Pin 1 I mean the leftmost pin above the LCD.  Pin 1 is gnd but Pin 4 is not grounded, yet all the solder joints look good.

Pin 2 has 5v, 3 has 1,84v, 7,8,9 and 10 have 5v, as do 13 and 14.  Pin 15 has 4v.  Pin 12 cycles around to three diff voltages.  

If you can make sense of this, that'd be great!


Mont Pierce KM6WT
 

On Mon, Aug 30, 2021 at 05:32 AM, Wayne Robertson wrote:
By Pin 1 I mean the leftmost pin above the LCD.  Pin 1 is gnd but Pin 4 is not grounded, yet all the solder joints look good.

Pin 2 has 5v, 3 has 1,84v, 7,8,9 and 10 have 5v, as do 13 and 14.  Pin 15 has 4v.  Pin 12 cycles around to three diff voltages.  
If you look at the QCX schematics in the assembly manual, you will see the following:
 
  • Pins 1, 5 and 16 are tied to ground.
  • Pin 4 connects to the wiper of R47 POT and part of a voltage divider circuit.
  • Pins 7-10 are unused and not connected.  The 5v you're seeing is internal pull-ups from inside the LCD.
  • Pin 11 goes to PD0 (RXD) on the processor, and is shared with the CAT Interface RX serial data
  • Pin 12 goes to PD1 (TXD) on the processor, and is shared with the CAT Interface TX serial data, the changes in voltage is from the TX serial data

Links to the QCX+ Hi Res black and white schematics are found on the QCX+ webpage (click here) just above the "Firmware" heading.  The QCX classic, QCX+ and QCX-mini are all the same basic circuit design with the mini having some components changed to lower power consumption parts.



For the issue with the "Two Rows" of blocks on the LCD, I'll let the more experienced "Julian" help troubleshoot.
It does indicate that the LCD was initialized, so some communication from the processor to LCD is occurring...



73
km6wt


Mont Pierce KM6WT
 

On Mon, Aug 30, 2021 at 06:21 AM, Mont Pierce KM6WT wrote:
  • Pin 4 connects to the wiper of R47 POT and part of a voltage divider circuit.
  •  
Sorry, need my eyes checked. 

LCD pin 3 (not 4) connects to the wiper of R47 POT and part of a voltage divider circuit

LCD pin 4 is the LCD Register Select signal (LCD_RS). 
It's pulled low to write to the Instruction Register.
It's pulled high to write to the Data Register.

Mont




 

I'm not sure how my name warranted quotes, Monte... am I to be reduced to a mere metaphor?  :-) 
Just kidding... and I'm not sure about being more experienced: you're just as good at this as I am, and at least equally valuable.
Actually, I like the tag teaming we do: we keep an eye on each other, and that helps everybody.
Don't you agree?
--
Julian, N4JO.


Wayne Robertson
 

Julian and Mont, a strange thing is going on.  In the schematic on p.84 of the assembly manual, the 2x5 JP101 is shown with Pin 1 in upper left corner.  
But, in checking voltages and connex to gnd, on my board Pin 1 that goes to gnd is in lower right corner.  It is as if the device is completely upside down as the Pins 2, 4, and 6 in my looking-glass world confirm Pin 1 as lower right corner.  

Am I reading this wrong or do I have a bizarre problem?

Many thanks.


Arv Evans <arvid.evans@...>
 

View from the front versus view from the back...?

_._


On Tue, Aug 31, 2021 at 2:13 PM Wayne Robertson <k4wk@...> wrote:
Julian and Mont, a strange thing is going on.  In the schematic on p.84 of the assembly manual, the 2x5 JP101 is shown with Pin 1 in upper left corner.  
But, in checking voltages and connex to gnd, on my board Pin 1 that goes to gnd is in lower right corner.  It is as if the device is completely upside down as the Pins 2, 4, and 6 in my looking-glass world confirm Pin 1 as lower right corner.  

Am I reading this wrong or do I have a bizarre problem?

Many thanks.


 

Your  assessment is correct: pin 1 is in the bottom right corner. The connector is rotated 180 degrees from the schematic.
A quick check is to ring out the bottom left pin (pin 2) of the display connector with the top left pin (pin 5) of the ISP connector just above it: they both have 5V on them, and will ring as a short.

As I've said on several occasions, be very careful with pin 6, as it has 12V on it. If you accidentally short it to pin 10, for example, you lose the display and the processor. There will be no prisoners. Checking that pin for shorts is part of my first time start up check list.
--
Julian, N4JO.


 

Sorry, I meant "if you short it to pin 8".

--
Julian, N4JO.


Wayne Robertson
 

Julian, are you saying the "connector is rotated 180 degrees from the schematic" as it ought to be or are you saying it is incorrectly installed upside-down?


 

I'm saying that pin 1 of the connector on the circuit board is at 180 degrees from what the picture of the connector on the schematic suggests that it would be.

The schematic suggests that pin 1 is the "Northwest" position on the circuit board. It isn't: it's in the "Southeast" position on the circuit board, looking at the circuit board in the same orientation as if you were operating it, which is with the BNC on the top of the board, sticking out to the right..

So you cannot assume the orientation of the connector on the circuit board matches the orientation in the schematic.

I hope that's clearer.
--
Julian, N4JO.


Wayne Robertson
 

Thank you; clear now.

So, the gnds and voltages check out yet the LCD is still blank or shows 1 or 2 rows of rectangles, depending on contrast setting of R47.  Anyone have any other ideas, or should I reach out to Hans?

Thanks Julian and Mont.

73, Wayne  


Alan G4ZFQ
 

Wayne
You are describing it displaying ONE row of blanks. Only both when the control is excessively advanced.
Here http://www.qrp-labs.com/qcxmini/trouble.html#blocks it says that the processor is not talking to the display.
Check out the processor.

73 Alan G4ZFQ


M0PWX
 

If R47 is correctly working the contrast of the display then the other issues can be the controller chip on the board IC2 (long chip in socket) or the data lines to the display

 

So back to basics

 

Check IC2 is in socket right way round

Check no pins bent (lift the chip slightly and make sure all pins are engaged in socket)

Check chip is fully seated in socket

Check solder joints on Socket (reheat to make sure)

Voltage  VCC pin 7 (5v)

Voltage VCC PAD 7 (5v)

Is chip hot to touch (if yes likely dead)

 

Check solder joints 20mhx XTAL

 

The next thing is the socket for the display

 

Check joints both sides (main board and display board) for bridges and cold joints (reheat and resolder to make sure)

 

What test equipment do you have? Just a multimeter? Oscilloscope?

 

73

 

Peter

 

From: Wayne Robertson

 

Thank you; clear now.

So, the gnds and voltages check out yet the LCD is still blank or shows 1 or 2 rows of rectangles, depending on contrast setting of R47.  Anyone have any other ideas, or should I reach out to Hans?

Thanks Julian and Mont.

73, Wayne  

_._,_._,_

 


 

As Alan implies, and as I said in my first response, only a single row of black rectangles implies that that display hasn't been successfully initialized. Yes, you might get two rows if you advance the contrast trimmer to one end, but if you get one row at any time, that is a bad indicator,

I think Monte is on to something...

Going back to your second post, you said "Pin 2 has 5v, 3 has 1,84v, 7,8,9 and 10 have 5v, as do 13 and 14.  Pin 15 has 4v. 
Analyzing...
Pin 12 cycles around to three diff voltages.  "
Pin 2 is Vcc - that's good
Pin 3 is display control, that's OK
Pins 7, 8, 9 and 10 are display data pins D0 though D3, which are not used, and will float high, that's good
Pins 13 and 14 are display data pins 6 & 7. I'm not sure I'm happy with those being stuck at at 5V, because..
Pin 12 is cycling between various voltages. This is what you will see on a DVM if the pin is carrying digital data, and the fact that it is cycling means that the processor is talking to it. This means that pins 13 and 14 should also show activity.

(Monte, I don't the CAT interface is a factor here: the QCX only speaks CAT when spoken to, and OP hasn't mentioned CAT is in use. Please correct me if I'm incorrect).

Wayne, please check the D6 and D7 connections between the processor and the display.

--
Julian, N4JO.


 

Peter,
I believe that if he's getting toggling on at least two of the data lines than the processor is at least attempting to talk to the display. I believe that the CAT interface isn't a factor here.
Did you catch anything in the dialog that has you suspect otherwise?
--
Julian, N4JO.


M0PWX
 

Hi Julian

 

I just approached it from the contrast pot seemed to be working as expected so it had to be data line related, so start at the beginning with the obvious basics

 

So check the microcontroller (pins bent etc) if not got to be a solder joint

 

So little info really other than detailed info on contrast pot and basic voltages

 

As you have picked up if there is data on several lines the microcontroller must be running, that lets out the XTAL and indicates chip is in socket the right way round

 

But could still be a bent pin on microcontroller, chip not fully seated or one or more poor solder joint on the any of the remaining data / control lines for the display

 

73

Peter

M0PWX

 

From: Julian N4JO

 

Peter,
I believe that if he's getting toggling on at least two of the data lines than the processor is at least attempting to talk to the display. I believe that the CAT interface isn't a factor here.
Did you catch anything in the dialog that has you suspect otherwise?
--
Julian, N4JO.

 


Mont Pierce KM6WT
 

On Tue, Aug 31, 2021 at 01:12 PM, Wayne Robertson wrote:
Julian and Mont, a strange thing is going on.  In the schematic on p.84 of the assembly manual, the 2x5 JP101 is shown with Pin 1 in upper left corner.  
But, in checking voltages and connex to gnd, on my board Pin 1 that goes to gnd is in lower right corner.  It is as if the device is completely upside down as the Pins 2, 4, and 6 in my looking-glass world confirm Pin 1 as lower right corner.  

Am I reading this wrong or do I have a bizarre problem?
On the QCX+ schematic there was also 2x? header that was numbered weird.  Hans found that his schematic software was numbering them that way. 

This is not a problem as long as you realize the numbers may be wrong.
Also, there is no way to plug in the display board backwards on the QCX+ or the mini.


The numbering does line up if you look at the top of the Display PCB, with the PCB turned up-side down:




Mont - km6wt


Mont Pierce KM6WT
 

Wayne:

First, lets go ahead and adjust your LCD contrast so it will be in the right spot for when you do get the text working.

Turn the contrast pot all the way CCW.  All blocks on all rows should be displayed.

Turn the pot CW till the blocks ALMOST disappear.
For now, it would be good if the blocks still show up, but, we don't want the black blocks to obscure the text when it is displayed.

Later, you'll probably want to turn R47 slightly more CW until the blocks disappear.


BTW, I was able to duplicate your symptoms on my Mini. I don't know if I've duplicated your exact problem, but this does give us a couple things to look at.

I took the display board off the main board, and ran jumper wires from the socket to the header.  Then I disconnected each signal wire, testing with it tied to ground, or floating.

There are two conditions I found that replicate your symptoms where the blocks appear on both lines, but no text is displayed.

  1. Pulled the jumper wire going to LCD_D6 and shorted it to ground.
  2. Pulled the jumper wire going to LCD_D4 and left it floating

(more to come)

73
km6wt