What is telephony? where does the VCC come from?

[budm]

Re: What is telephony? where does the VCC come from?

That bridge rectifier is on the main unit so more than likely that the two ~ pins are connected to the transformer winding.
What ACV do you get between those two ~ pins?

[keeney123]

Re: What is telephony? where does the VCC come from?

What would be good at this point is to determine on the remote board where the voltage is being generated. We know that the main board it want is generating the voltage on remote board. What we don't know is the link between the voltage on the main board and the remote. By ohming out the trace on the remote board with the R11 connector disconnected you will find out where it is coming from on the remote board. Once you find that then you will be able to find out the link from the main board. So you can physical look at the trace and follow it with the ohm meter. If the other people's input is that it is coming from a particular place that can be ohmed out to verify that is correct. Again the problem is the voltage on the chip on the remote board has to get 5volt min. 4.75 volts DC to work. Following this line of thinking will lead you to why there is no 5 volts DC on that chip. Sometimes, not always, engineers and physic professors know to much about the circuitry. They then think they can skip sets in troubleshooting. The problem happens when they make an error. Instead of a typical error it is complicated because steps have been skipped, so what I would do for your own benefit is when they tell you a particular thing verify that it is the case. I approach a problem like Archimedes. First we do not know anything about a problem, but we must make a decision. Once we make a decision we observe the outcome. Based on that outcome we then make another decision and so forth and so on. We end up getting better and better at dealing with a problem, but we are never perfect at the problem.

[stj]

Re: What is telephony? where does the VCC come from?

That bridge rectifier is on the main unit

damn, i thought i was looking at the slave panel!

[fzabkar]

Re: What is telephony? where does the VCC come from?

What would be good at this point is to determine on the remote board where the voltage is being generated. We know that the main board it want is generating the voltage on remote board. What we don't know is the link between the voltage on the main board and the remote. By ohming out the trace on the remote board with the R11 connector disconnected you will find out where it is coming from on the remote board.

The remote PCB is powered from the main board, not vice versa.

[fzabkar]

Re: What is telephony? where does the VCC come from?

AISI, the incoming supply at the remote PCB is regulated as follows:

      "15H"
    .---------. +1.875V .--------. +2.36V .-----------.
RJ11-B |     |  Cin  |    |  Cout  |      |
  o------>|--+-------+----|in  out|----+-----|      |
 -1.1V |   | |  |  |    |  |   |  MCU  |
    |   z |  |+  |    |  |+  |  RS485  |
    |   A |  ===  | LP2951 |  ===  | display |
    |   | |  ---  | reg  |  ---  |      |
    '------|--'  |  |    |  |   |      |
        |    |  '--------'  |   '-----------'
RJ11-C     |    | 100uF |     | 100uF   |
  o----------+-------+--------+---------+-----------'
 0V               |
                ===
                GND

The RJ11-B input appears to be an AC waveform sitting on a -1.1V DC bias.

I'm guessing that the "15H" component provides reverse polarity protection and voltage clamping.

The rectified input is filtered by Cin, but the voltage subsequently decays during the negative AC cycles. It appears that Cin could be leaky or low in capacitance, or perhaps "15H" is leaky.

Cout is charged during the peak of the AC input and appears to retain its charge during the negative AC cycles.

That's the only scenario that I can come up with to explain the observed measurements. It would REALLY help to see what is happening on a scope.

[keeney123]

Re: What is telephony? where does the VCC come from?

The remote PCB is powered from the main board, not vice versa.

Yes, I know this, but I do not know if there is a voltage step down to get 5 volts on the remote board. He verified this when he unplug the R11 connector and got o volt across the transmitter IC on the remote bd. There could still be some type of weird grounding that the designer created or it is just that the voltage is coming from the main board. The voltage could be of a higher amount and a DC to DC converter could be stepping it down on the remote board. The problem still exist on the remote board as not having at least 4.75 volts DC on the transmit IC. The IC will not function with less then this so no communication will occur between the two boards.

[scampo77]

Re: What is telephony? where does the VCC come from?

cant I just put a NPN transistor in place of the 15H and see what happens? should I order new communication ICs for each end?

it makes sense that something in the remote side is causing the 4.5v to drop, when I unplug the remote the output voltage bounces back up to 4.5-5 and when I plug the remote back in, the voltage drops again to 3v

[fzabkar]

Re: What is telephony? where does the VCC come from?

I wouldn't touch the remote board. The problem is with the RJ11-B voltage on the logic board. Trace it back to its source, probably near the bridge rectifier. Test for continuity with the + terminal of the bridge, or each of the PCB interconnect pins.

[keeney123]

Re: What is telephony? where does the VCC come from?

It is difficult of working without schematics. For fzabkar theory you could leave the RJ11 connectors unconnected and follow the voltage as he said to find out if there is indeed a voltage problem on the main board. You did say every thing on the main board was working and only the remote was not working? This is how you trouble shoot a board. You follow one train of thought to see if it is correct and if it is not then you modify you train of thought.

[keeney123]

Re: What is telephony? where does the VCC come from?

Just one more thing. While your troubleshooting this circuit keep in mind that why the two boards are not talking to each other is because the voltage on the communication chip on the remote is not getting at least 4.75 volts. Right now it has nothing to do with the communication lines between the two boards. A good procedure to follow is check voltages first. Then check the control lines. Lastly check the data and address lines. At all possible have a schematic in hand.

[scampo77]

Re: What is telephony? where does the VCC come from?

I have found a second non functioning logic board, I have something I can poke and remove parts from to see traces better. please don't comment that the caps are corroded or the solder traces are bad. I am dissecting this one with the intention of throwing it away when I am done with it.

I have removed all of the RJ11 jacks on this donor board to better see the traces. this "B" port seems to go to the neighboring RJ11 port for the auto start module which I do not have hooked up. then it goes to a capacitor then to me it looks like ground, it takes off and goes all over the place on both sides of the board.

I am now getting 0vdc at the "B" terminal that I am chasing around. And I am getting 4.5VDC on terminal "D" with or without the remote board attached

I have tried calling multiple repair centers and Magnum directly with all of the power of my charm and non of them have access to diagrams or schematics or any engineering side of these repairs. These have been designed to be replaced like computer video cards, the only downside is that the logic board is $400 and the remote board is about $300 and the entire inverter is about $2000. All of these options are way out of my budget.

[keeney123]

Re: What is telephony? where does the VCC come from?

So on the main logic board the regulator 295151ACS is a 5 volt regulator because it has no XX numbers after it. The XX numbers would be like -2.5, -3.0. This is the data sheet for that chip.



If this is what is generating your 5 volts regulated to the remote board Then it has very tight tolerances. It you are reading 4.5 volts that would be out of spec. I also noticed that there is way too much solder on these components on the main logic board. I know if a capacitor gets to much heat near its plate you can damage to connection in a way that the cap will appear to work, but it will not perform correctly.

[scampo77]

Re: What is telephony? where does the VCC come from?

GOOD NEWS!!

I found a damaged trace under one of the RJ11 jacks. (photo enclosed) this connected "B" terminal to the fuse. the huge trace I was chasing around turned out to be B+. It is de coupled by a cap and protected by a fuse (look on the previous post photos) I repaired the trace and now I have MUCH better voltages to work with.

Now the "B" terminal is B+ and I have much better voltages on the remote board (photo enclosed).

The inverter is still going into some kind of protect mode. As soon as I apply battery voltage I throw a big relay and it will not power up like it was before. I am hoping this burnt trace is a step in the right direction.

I have enclosed measurements from my suspect 5v regulator and I have rock solid 5.00 VDC.

[budm]

Re: What is telephony? where does the VCC come from?

That is good progress, so the remote is fed by 5VDC not AC which makes a lot more sense.

[fzabkar]

Re: What is telephony? where does the VCC come from?

The remote is fed by 14.7V, not 5V.

[keeney123]

Re: What is telephony? where does the VCC come from?

GOOD NEWS!!

I found a damaged trace under one of the RJ11 jacks. (photo enclosed) this connected "B" terminal to the fuse. the huge trace I was chasing around turned out to be B+. It is de coupled by a cap and protected by a fuse (look on the previous post photos) I repaired the trace and now I have MUCH better voltages to work with.

Now the "B" terminal is B+ and I have much better voltages on the remote board (photo enclosed).

The inverter is still going into some kind of protect mode. As soon as I apply battery voltage I throw a big relay and it will not power up like it was before. I am hoping this burnt trace is a step in the right direction.

I have enclosed measurements from my suspect 5v regulator and I have rock solid 5.00 VDC.

So now that problem is fixed. We need to concentrate on this new problem. We need to know where the battery voltage is going too on the inverter. It is possible that the relay is held in by another circuit.

[budm]

Re: What is telephony? where does the VCC come from?

The remote is fed by 14.7V, not 5V.

I am confused:
Per Post 45 : AISI, the incoming supply at the remote PCB is regulated as follows: per diagram: So RJ-1B is fed by 14.7V? Feeding 14V to drop down to feed LP2951 3V? That is lots of Vdrops on this LDO.

Post 52: So on the main logic board the regulator 295151ACS is a 5 volt regulator because it has no XX numbers after it. The XX numbers would be like -2.5, -3.0. This is the data sheet for that chip.



If this is what is generating your 5 volts regulated to the remote board Then it has very tight tolerances. It you are reading 4.5 volts that would be out of spec. I also noticed that there is way too much solder on these components on the main logic board. I know if a capacitor gets to much heat near its plate you can damage to connection in a way that the cap will appear to work, but it will not perform correctly.

Post 53 'I have enclosed measurements from my suspect 5v regulator and I have rock solid 5.00 VDC.'

So what is the Voltage feeding the Remote Module for sure?

[budm]

Re: What is telephony? where does the VCC come from?

Double posted.

[fzabkar]

Re: What is telephony? where does the VCC come from?

budm, look at the 4th photo in post #53. The reading of 4.5V appears to be for one of the data pins of the RS485 transceiver IC, not the power supply.

BTW, I agree that the 14V-5V in-out voltage differential is absurdly high, but that's the way it appears to be designed. If we knew the identity of the "15H" part, then perhaps we could determine the allowable input range.

[stj]

Re: What is telephony? where does the VCC come from?

volt-drop over that crappy cable must be taken into account by the designers.