Juma TRX2A - Voltage supply problem in Main Board

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Juma TRX2A - Voltage supply problem in Main Board

Postby OH2NOS » 02 Jan 2012 19:59

Hi Matti!

My Juma TRX2A –project is in such status that I have switched it on.

DDS card is up and running nice. I met problems when I tested voltage supply in Main Board.

Based on Juma Manual I measured voltage levels over capacitors C65, C63 and C64. I am supplying Juma with accumulator which pole voltage is 12,1V.

C65: U=11,8V (instruction values 12V...15V) – this is ok from my point of view.
C63: U=8,6V (instruction values 4,8V...5.2V) – here is over voltage.
C64: U=1,0V (instruction values 9,5V...10,5V) - here is under voltage.

I measured also input voltage to the regulators 1 and 2 (LP2951). I both cases it is 11,8V in pin 8. Is it possible that these both regulators could be defected?

How I could check if the problem is in regulators or in somewhere else?

Before I was able to place this question to the Juma Forum, I got hint to check capacitors above and resistors R31, R66 and the position of regulators 1 and 2.

I did these inspections and soldered pins of regulators and installed C64 ones again. Regulators are installed in correct position. But, measure results over C65, C63 and C64 were the same again as before!

The only what I am thinking now is to change the regulators. Now I am handless how to continue with error fixing?


73, Saku OH2NOS “JA”
Ps. “JA” = Juma Addicted
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Re: Juma TRX2A - Voltage supply problem in Main Board

Postby OH7SV » 03 Jan 2012 08:58

Saku,

By default ICs are not broken if you have not overstressed them with wrong polarity or some other "brutal" way.
Additionally LP2951 is not very sensitive for ESD.

There has not been any problems in TRX2 voltage regulators. You must have something wrong.
Check carefully visually everything around the regulators on main board. Check also the polarity and correct IC type.

The +5V voltage (REG1) is set by the LP2951 internal resistors, pin 7 connected to pin 6.
The +10V voltage (REG2) is set by the external resistors R31 and R66.

When LP2951 regulator is working properly there should be +1.2V at pin 7 to GND. Pin 7 is the feedback pin.

73 Matti OH7SV
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Re: Juma TRX2A - Voltage supply problem in Main Board

Postby OH2NOS » 03 Jan 2012 20:50

Hi Juha!

Life goes on but some problems stay.

Some progress has happened. First, I downloaded datasheet of LP2950 (2951). Now I got better understanding about pins and their meaning.

Reg 1: Pin 2 was badly soldered and it is now connected to pin 1 and the regulator works correct! Output voltage is 5,06V and feedback voltage in pin 7 is 1,23V.

Reg 2: Not any progress sofar. Input voltage in pin 8 is 11,8V. Output voltage in pin 1 is the same 1,02V as before and feedback voltage in pin 7 is 0,187V.

C64: U=1,02V (instruction values 9,5V...10,5V) - here is under voltage.

Connection from pin 1 to R31 and C64 is ok. Connection from pin 7 to between R31 and R66 is ok. Connection from pin 4 to ground is ok. Then I Then I measured also R31, R66 and C64 individually. All these components and connections are ok.

What the value of pin 7 (0,187V) tells to you? Is it a mark about defect in the regulator or does it tell about overload behind the regulator? I checked the PCB but I didn´t remark any clear problem. What next?

73, Saku OH2NOS “JA”
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Re: Juma TRX2A - Voltage supply problem in Main Board

Postby OH7SV » 03 Jan 2012 21:35

Saku,

Good progress :D +5V is fine now.

Most probably something is loading the +10V rail and the regulator REG2 is in current limit state. If it is overload, you should feel heat when touching the REG2. Pin 7 voltage will also go down if regulator is in current limit state.

1V output voltage indicates that there is not a very solid short to GND from +10V line. It can be wrong polarity component or resistor instead of a capacitor etc. The LP2951 current limit is about 160mA. 1V ouput corresponds approx 6 to 7 ohms load. Shut down TRX2 and measure the resistance from +10V line to GND. If it indicates 5...10 ohms, it can be very thin copper remainig on PCB. If it indicates higher ohms, it can be a wrong polarity OPAMP A1...A11 and A13 acting as a diode to GND. Note that the +10V goes also to the filter board. Remove the filter board to isolate the problem.

Continue searching the problem by checking everything which is connected to the +10V line. I'm sure you will find it soon.

73 Matti OH7SV
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Re: Juma TRX2A - Voltage supply problem in Main Board

Postby OH2NOS » 06 Jan 2012 13:09

Hi Matti!

I have good and bad news for you - bad first!

I have not been able to fix the problem with 10V power supply. Good news is that I have done lot of measurement for tackling the problem but without success. Measurements which I have used are Fluke 179 Multimeter and Fluke 105B Scopemeter.

1. Polarity of condensators is right. I have checked it three times and my wife did it ones (;-D).
2. I disconnected RF Filter and measured its DC-resistant from J3: between pin 1 and 6. Result was 445 ohm.
Following measurements I did for the Main Board only (disconnected fully):
3. Resistant between C64 (+) and ground is 4,6 kohm.
4. Resistant between C51…C61 and ground is the same 4,6 kohm. Every condensator is measured individually.
5. Resistant between R83 and ground (OP AMP REF) is the same 4,6 kohm.
6. Resistant between R14 and ground (PRE AMP REF) is the same 4,6 kohm.
7. I checked solders of A1 to A11 and re-soldered them.
8. Then I checked conductivity from C64 to supply pin of A1 to A11.
9. Then I checked conductivity from GND 1(2) point to ground pin of A1 to A11. In each case I got the lowest values of Multimeter (0,2 ohm).

I am quite persistent and will get my Juma up and running. Give me couple of new hints what I should do next?

73, Saku OH2NOS “JA”
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Re: Juma TRX2A - Voltage supply problem in Main Board

Postby OH7SV » 06 Jan 2012 14:55

Ok Saku,

Let's continue with smaller steps.

1. I did not mean the RF Filter but the 1st AF filter which is plugged on the main board, marked FILTER1 on the PCB. Remove it and check if it helps with the +10V.

2. Is the +10V regulator REG2 getting hot when you keep power on for some time?

73 Matti OH7SV
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Re: Juma TRX2A - Voltage supply problem in Main Board

Postby OH2NOS » 06 Jan 2012 21:14

Hi Matti!

I checked the Filter 1, its resistance between pins 2 to 3/4 is 7,2 kohm. Previous measurements I made with pure Main Board without Filter 1. The whole resistance, when Filter 1 is connected, between C64 (+) and ground is 3,9 kohm.

Then I checked A1 to A11 with magnifying glass against layout picture and what I found! A1 to A9 are for sure correct installed. But now I have bad feelings that I have installed A10 and A11 180 degrees in wrong position! If it is possible to add a picture to Juma Forum I do it. Otherwise I send the picture by mail to you.

Let me know if I did correct conclusion or not!

73, Saku OH2NOS “JA”
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Main Board.jpg
A10 and A11
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Re: Juma TRX2A - Voltage supply problem in Main Board

Postby OH7SV » 06 Jan 2012 21:21

Saku,

I think you found the main problem now :)
The OPAMPs A10 and A11 are installed 180 degrees in wrong position!
Remove them and check the +10V. If the voltage is ok you can try if those OPAMPs are still ok.

73 Matti OH7SV
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Re: Juma TRX2A - Voltage supply problem in Main Board

Postby KH2BR » 06 Jan 2012 21:23

I looked at mine and it appears that you have them 180 degrees out of place. the sloped side is to the back of the radio.
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Re: Juma TRX2A - Voltage supply problem in Main Board

Postby OH2NOS » 18 Jan 2012 12:35

Hi Matti!

I have been out of hobby last two weeks, but now I inform that 10V line is up and running. When A10 and A11 was turned in correct position output voltage of REG 2 was 10,2V (or 10,3V), but anyway the reason of problem was wrong position of A10 and A11.

I make more stupid question for becoming cleverer! I have not yet done any adjustments (Manual pages 36 to 41) because lack of time. Next weekend I will continue again. When voltage supply problem was fixed I connected antenna to Juma and listened shortly. What I heard, was pure noise. I suppose that I should listen something (real signal) before adjusting! I am right? Based on this assuming I suppose that antenna signal doesn’t come correct in now.

I try to borrow signal generator for weekend. If I don’t get it I have to try to do it with antenna. I am just starting to study RX section of main board. I don’t have any idea how big the input signal (mV) of antenna can be in normal case. Question: if I measure signal from antenna connector its value should be 66 times bigger in pin J6-1. Is it so?

Value of voltage in pin 1 of A1-A is 8Vp-p. What these values are in pin 1 of A3-A, in J6-1, J6-6, J6-7 and J6-8? How about between R91 and ground?


73, Saku OH2NOS “JA”
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