Newly built QCX+ processor works intermittently #qcx


rahul@...
 

I built a QCX+ 40 m. At first it did not boot but thanks to helpful troubleshooting tips provided by the community and rechecking my solders it suddenly worked out of nowhere. Sometimes it starts fine. Sometimes it just displays the single row of blocks. How do I confirm if this is a power issue?


Arv Evans <arvid.evans@...>
 

Rahul

Sounds more like a problem with the connections 
between CPU and LCD (LCD failing to get initialized).

Arv
_._

On Tue, Aug 18, 2020 at 11:40 AM <rahul@...> wrote:
I built a QCX+ 40 m. At first it did not boot but thanks to helpful troubleshooting tips provided by the community and rechecking my solders it suddenly worked out of nowhere. Sometimes it starts fine. Sometimes it just displays the single row of blocks. How do I confirm if this is a power issue?


rahul@...
 

Thank you Arv. I had to desolder my right angle header pins that connect to the front panel PCB since I soldered them wrong in the first place and they're not in the best condition right now. Would a bad LCD connection be caused to those bent connectors? They mate just fine


Arv Evans <arvid.evans@...>
 

Touching a soldering iron to both sides of each pin might be a good step, but be careful that you do not lift a solder pad.  

With the CPU and LCD unplugged (and power off) you can use an ohm meter to verify conductivity for each lead between these two devices.  LCD failing to initialize frequently has been traced to a poor connection (data or enable) between the controller and the LCD.  If the crystal is oscillating you should see some data being sent on leads between these two devices.

Arv
_._


On Tue, Aug 18, 2020 at 12:59 PM <rahul@...> wrote:
Thank you Arv. I had to desolder my right angle header pins that connect to the front panel PCB since I soldered them wrong in the first place and they're not in the best condition right now. Would a bad LCD connection be caused to those bent connectors? They mate just fine


rahul@...
 

When the LCD displayys a single row of blocks , I took a reading and this is what I get when compared to the manual. This is running off a 12 V PSU 

+-------------------------+----------+----------+-----------------------+
| Pin                     | measured | Expected | Description           |
+-------------------------+----------+----------+-----------------------+
| LCD pin 1 (leftmost)    | 0        | 0        | LCD VSS supply pin    |
+-------------------------+----------+----------+-----------------------+
| LCD pin 2               | 4.8      | 4.94     |  LCD VDD supply pin   |
+-------------------------+----------+----------+-----------------------+
| LCD pin 3               | 4.9      | 0.57     | LCD Contrast          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 4               | 4.8      | 4.92     |  LCD RS pin           |
+-------------------------+----------+----------+-----------------------+
| LCD pin 5               | 5        | 0        | LCD RW pin            |
+-------------------------+----------+----------+-----------------------+
| LCD pin 6               | 5        | 0        | LCD E pin             |
+-------------------------+----------+----------+-----------------------+
| LCD pin 7               | 5        | 1.08     |  LCD DB0 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 8               | 4.9      | 1.08     |  LCD DB1 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 9               | 4.9      | 1.06     |  LCD DB2 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 10              | 4.9      | 1.04     |  LCD DB3 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 11              | 0        | 0        |  LCD DB4 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 12              | 0        | 4.94     | LCD DB5 pin           |
+-------------------------+----------+----------+-----------------------+
| LCD pin 13              | 0.076    | 4.92     |  LCD DB6 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 14              | 1.168    | 0        |  LCD DB7 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 15              | 5        | 4.41     |  LCD backlight anode  |
+-------------------------+----------+----------+-----------------------+
| LCD pin 16 (rightmost)  | 0        | 0        | LCD backlight cathode |
+-------------------------+----------+----------+-----------------------+


Gregg Myers
 

Rahul,

Pin 3, your contrast adjustment looks very off from expected. I would start there. Check R47 which Is setting the contrast voltage to pin 3. You should not see 5 volts unless your R47 is cranked all the way to one end. Since you are seeing something intermittent, you might try gently wiggling R47, R65 and/or check for bad connection/short somewhere there. Attached is the schematic of that region.

73,
Gregg W7GRM


On Tue, Aug 18, 2020 at 3:40 PM <rahul@...> wrote:
When the LCD displayys a single row of blocks , I took a reading and this is what I get when compared to the manual. This is running off a 12 V PSU 

+-------------------------+----------+----------+-----------------------+
| Pin                     | measured | Expected | Description           |
+-------------------------+----------+----------+-----------------------+
| LCD pin 1 (leftmost)    | 0        | 0        | LCD VSS supply pin    |
+-------------------------+----------+----------+-----------------------+
| LCD pin 2               | 4.8      | 4.94     |  LCD VDD supply pin   |
+-------------------------+----------+----------+-----------------------+
| LCD pin 3               | 4.9      | 0.57     | LCD Contrast          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 4               | 4.8      | 4.92     |  LCD RS pin           |
+-------------------------+----------+----------+-----------------------+
| LCD pin 5               | 5        | 0        | LCD RW pin            |
+-------------------------+----------+----------+-----------------------+
| LCD pin 6               | 5        | 0        | LCD E pin             |
+-------------------------+----------+----------+-----------------------+
| LCD pin 7               | 5        | 1.08     |  LCD DB0 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 8               | 4.9      | 1.08     |  LCD DB1 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 9               | 4.9      | 1.06     |  LCD DB2 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 10              | 4.9      | 1.04     |  LCD DB3 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 11              | 0        | 0        |  LCD DB4 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 12              | 0        | 4.94     | LCD DB5 pin           |
+-------------------------+----------+----------+-----------------------+
| LCD pin 13              | 0.076    | 4.92     |  LCD DB6 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 14              | 1.168    | 0        |  LCD DB7 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 15              | 5        | 4.41     |  LCD backlight anode  |
+-------------------------+----------+----------+-----------------------+
| LCD pin 16 (rightmost)  | 0        | 0        | LCD backlight cathode |
+-------------------------+----------+----------+-----------------------+


Jim Painter
 

Rahul, pins 1,5 and 16 are tied to ground. 1 and 16 are 0 volts. Pin 5 should be too. Looks like a bad solder connection.

Jim...kq3s


On Aug 18, 2020, at 6:43 PM, Gregg Myers <gregg.w7grm@...> wrote:


Rahul,

Pin 3, your contrast adjustment looks very off from expected. I would start there. Check R47 which Is setting the contrast voltage to pin 3. You should not see 5 volts unless your R47 is cranked all the way to one end. Since you are seeing something intermittent, you might try gently wiggling R47, R65 and/or check for bad connection/short somewhere there. Attached is the schematic of that region.

73,
Gregg W7GRM
<IMG_3075.jpg>


On Tue, Aug 18, 2020 at 3:40 PM <rahul@...> wrote:
When the LCD displayys a single row of blocks , I took a reading and this is what I get when compared to the manual. This is running off a 12 V PSU 

+-------------------------+----------+----------+-----------------------+
| Pin                     | measured | Expected | Description           |
+-------------------------+----------+----------+-----------------------+
| LCD pin 1 (leftmost)    | 0        | 0        | LCD VSS supply pin    |
+-------------------------+----------+----------+-----------------------+
| LCD pin 2               | 4.8      | 4.94     |  LCD VDD supply pin   |
+-------------------------+----------+----------+-----------------------+
| LCD pin 3               | 4.9      | 0.57     | LCD Contrast          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 4               | 4.8      | 4.92     |  LCD RS pin           |
+-------------------------+----------+----------+-----------------------+
| LCD pin 5               | 5        | 0        | LCD RW pin            |
+-------------------------+----------+----------+-----------------------+
| LCD pin 6               | 5        | 0        | LCD E pin             |
+-------------------------+----------+----------+-----------------------+
| LCD pin 7               | 5        | 1.08     |  LCD DB0 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 8               | 4.9      | 1.08     |  LCD DB1 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 9               | 4.9      | 1.06     |  LCD DB2 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 10              | 4.9      | 1.04     |  LCD DB3 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 11              | 0        | 0        |  LCD DB4 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 12              | 0        | 4.94     | LCD DB5 pin           |
+-------------------------+----------+----------+-----------------------+
| LCD pin 13              | 0.076    | 4.92     |  LCD DB6 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 14              | 1.168    | 0        |  LCD DB7 pin          |
+-------------------------+----------+----------+-----------------------+
| LCD pin 15              | 5        | 4.41     |  LCD backlight anode  |
+-------------------------+----------+----------+-----------------------+
| LCD pin 16 (rightmost)  | 0        | 0        | LCD backlight cathode |
+-------------------------+----------+----------+-----------------------+


rahul@...
 

THANK YOU ALL!
It was a bad LCD header that I mangled. Got a new one and she works like a charm


Arv Evans <arvid.evans@...>
 

Rahul

Congratulations on your success.  Usually it is something simple that takes enormous amounts of time to troubleshoot.  

Arv
_._


On Thu, Aug 20, 2020 at 3:24 PM <rahul@...> wrote:
THANK YOU ALL!
It was a bad LCD header that I mangled. Got a new one and she works like a charm