What is telephony? where does the VCC come from?

[keeney123]

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

So this is the problem 2 volts at pin8 when you need a minimum 4.75 VDC to operate that chip. I am not sure but I would say the 5 volts is being generated on this remote board and is being fed by another connector. If you unplug this R11 connectors and leave the other connectors connected then measure the same two points again pin 8 and pin 5 what do you get?

[scampo77]

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

There is no other connectors, only these 4 conductors on the phone cord. I am pretty sure the power comes from this logic board leaving on the red "D" terminal.

I was wondering if I could just jam 5v to this D terminal, to see what happens? I don't know if this is a good idea or not.

[keeney123]

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

If the voltage goes away between pin 8 and pin5 with the R11 connectors disconnected we will "assume" the 5 volts is coming from the main board.If it is coming from the main board we need to determine which board is causing this. So now I would measure the voltages on the R11 connector while it is unplugged from the remote board in reference to the gnd pin on the R11 connector that is unplugged. See if the voltages change their reading while unconnected as oppose to connected. If they do we will again "assume" the problem lays in the remote board. Also when the R11 connectors are unconnected from the remote bd. go the the main board and measure the same points on the main board. This will verify what ever the main board is putting out it is getting to the end of the cable if both readings are the same.

[fzabkar]

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

Sipex was acquired by Exar.

Here is the current support page and datasheet for the SP483E:

http://www.exar.com/connectivity/tra.../rs485/sp483e/
http://www.exar.com/common/content/d...et&part=sp483e

R5F21256SNFP, Renesas, R8C, SINGLE-CHIP 16-BIT CMOS MCU, 2.2V - 5.5V (f(XIN) = 5 MHz):

[fzabkar]

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

The component marked "F" on the logic board appears to be a polyswitch resettable fuse. I would expect that it would be protecting the outgoing supply. What voltage do you measure there? Does it connect to the RJ11 jack?

[keeney123]

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

The F is near the RJ11 jack right above the TP10 on your picture of the main board. You can do that, but you still are going to have to determine which board is causing your problem.

[fzabkar]

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

The F is near the RJ11 jack right above the TP10 on your picture of the main board. You can do that, but you still are going to have to determine which board is causing your problem.

ISTM that the "logic" board has a problem.

The A&D differential pair appear to connect to the data pins of the SP483 transceiver, so that's OK. The B&C pair are the power pins. C is ground, so that looks OK, too. The OP needs to determine where the -1.1V is coming from. AFAICT, that should be a positive supply. I would look for any chip that might be a regulator. In fact I can see at least one LDO (Sipex SPX2951ACS) in the earlier photos.



There is also a DF04S bridge rectifier (near CON111). I wonder if that's the source of the negative voltage.

https://cdn.badcaps-static.com/pdfs/...415d4937ea.pdf

[scampo77]

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

The voltage defiantly drops to 0v on the remote board when I unplug the phone line. on the main logic board I get an unusual result, I get 4.2v when I unplug the remote and then I get 3v when I plug the rj11 in.

I have 0v on both sides of the F thing located below the 483ECN

while taking measurements for this photo. I moved the board someway that it didn't like and one of the big relays clicked and now everything is 0v, DAMMIT!!

now as soon as I connect the B+ it clicks the relay and now I have no remote to visually see what the hell is going on, I am so discouraged.

[scampo77]

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

so after throwing my hat in the air and kicking my cat across the room out of frustration, I came back and realized that my main logic board is not totally dead. I have power to most of the ICs I had before. I now have 4.25v at terminal D leaving the logic board and arriving at the remote board, The remote board is still not working.

I still have power to the 483ECN on the logic board, the only difference now is that I have 4.25v output to the red D circuit.

[fzabkar]

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

Is the supply to the remote unit actually AC, and are you actually measuring a DC offset of -1.1V on this supply??? An AC supply would resist galvanic corrosion.

Is there a rectifier and regulator on the remote PCB?

[scampo77]

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

Measuring A+B together with my meter on ACV I am getting 2.5VAC. I have no way to scope this reading but I suspect you are onto something.

If you look on post #6 there is a photo of the remote board, I don't think there is any rectification circuits here, but I'm not 100% sure what I am looking for.

[fzabkar]

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

The two middle pins (B & C) would be the power pins.

What is that other 8-pin IC on the remote PCB? Where do those electrolytic capacitors connect?

[budm]

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

Measuring A+B together with my meter on ACV I am getting 2.5VAC. I have no way to scope this reading but I suspect you are onto something.

If you look on post #6 there is a photo of the remote board, I don't think there is any rectification circuits here, but I'm not 100% sure what I am looking for.

Reverse the meter probes to see if you are still getting 2.5 VAC.
is this the remote board or main board? https://www.badcaps.net/forum/attach...5&d=1451312753, based on post 6 showing the remote unit.
So you do have bridge rectifier on the remote board. So you are getting AC between the two ~ pins of the bridge? You indicated 0V, and 5V and 7.5V, diode check OK for the bridge? 2.5Vac is not enough to produce 5VDC from the bridge.

[scampo77]

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

if I measure for ACV on pins on B&C then I get about 2.5VAC and if I reverse the probes I get 3.5VAC, but its really bouncing around on my meter, It fluctuates by.25v up and down.

I tried to get some photos of the capacitors and also the ICs on the remote. the other 8 leg IC is labeled MTAK 2951 ACMC. sorry I tried to get as many photos as I could but they did not come out very well. These are all photos of the remote board, when I remove the phone cable, everything goes to 0

[scampo77]

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

Bud, that photo you linked is the main logic board, I will try my best to label all the photos moving forward.

[scampo77]

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

I have no idea what this piece is or what to look for, I just see that there is a "+" and a "-", so I checked for ACV and found some. I have never seen ACV on a circuit board before

[fzabkar]

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

The LP2951ACM (on the remote PCB) is a linear voltage regulator. It comes in adjustable and fixed voltage versions. I suspect that yours has a 5V output.

The 3-terminal component (15H) near the edge of the remote PCB could be a rectifier diode plus a zener clamp (?).

[stj]

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

I have no idea what this piece is or what to look for, I just see that there is a "+" and a "-", so I checked for ACV and found some. I have never seen ACV on a circuit board before

see if any of the 4 pins on that are shorted together.

[scampo77]

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

On the main logic board at the rectifier, I have 5 ohms between the 2 pins on the right hand side, all other combinations have very high resistance.

the picture enclosed is the remote PCB with voltage measurments

[stj]

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

that 5ohms sounds very wrong,
does it read 5ohms wih the cable disconnected?