Need help with Panasonic 616/308 proprietary phone

[cloyd]

I think I will be able to find and check the fuses.  I have a multimeter but never learned how to use it.  I understand what you mean by connecting the 308 to an uninstalled jack and testing it.  I'll use YouTube to figure out the multimeter.  I am glad you guys haven't given up yet!  I'll certainly check the fuses tonight.
Tina

[unbeldi]

Well, no better time to figure out that instrument.

From magnifying the image, you can actually see the wires inside the fuse.
Set your multimeter to a low ohm scale, 2 ohms or 20 ohms, and touch the test probes to the metal caps at each end of the fuses.
The reading should be close to 0.00, zero.

You can also pull those fuses out of the socket and check them visually.

[cloyd]

Hello all,
I was able to find the two fuses last night and they looked OK.  I could see the wires inside and they are intact and not burned out.  I gave the whole board a once-over and could find no broken connections and no goo, bulges or blackened areas.  (I apologize for the technical lingo there.)  I would still like to try the multimeter; I have been working late and tend to crash early in the evenings.  Not a great time of day to be dinkin' around with electrical equipment or anything that requires a modicum of brain power.
Tina

[unbeldi]

Good work....  But visual inspection is really only good if it yields a result of "blown fuse".
The meter should be definitive.

[cloyd]

Well!  I'm feeling pretty chuffed!
I was having a hard time figuring out my cheap multimeter and then realized that the furnace guy had left his Fluke deluxe meter!  I feel pretty confident that I did it right.  We'll see what you all think.

I tested the outer pins on the cable that came with the phone and got continuity on each pin.
With the 308 unplugged, I tested the fuses and got .3 ohms on each.  Is that near enough to zero?

To be clear, to test the extensions, I plugged in a cable with a modular cord into one extension (at a time) and then plugged the other modular end into a disconnected wall jack.  Then, with the 308 plugged in and turned on, I measured the amps by putting the leads to the black and yellow connections in the wall jack.

The extension results:
ext.#/AmpsVolts
11 = 12.2
12 = 12.2
13 = 5.13
14 = 5.3
15 = 5.3
16 = 15.0
17 = 15.0
18 = 15.0

Do these numbers make sense?  Remember, extension 13 wasn't working with my standard phones.  (Unbeldi, I rewired my 302 to match another one that I have and now it works.  Sorry for the confusion.) 

I sure hope this narrows things down.  Let me know what this tells us.

Tina

[unbeldi]

Excellent!   Having a Fluke meter is deluxe, indeed.  One of the best brands.

Yes, 0.3 ohms is very good.  You have to figure into the equation the resistance of the probe wires, and those come out usually as a few tenths of an ohm.

Your table is great, and shows that you do have some problems (PS: no, your PBX I should have said).  You column should be labeled "Volts" not Amps, though.

12 to 13 volts is perfect, I am surprised how ports 16-18 can have such a high voltage, but it's not outrageous.  But ports 13-15 are way off, too low to run a PT, I think.  But I haven't tried running mine so low.
Something is wrong with your PBX.

PS: I don't see a reason off-hand why the voltages would vary so much... I have measured a 308... so I have to consult my circuit diagrams and think about it.

[unbeldi]

Did you by any chance also measure the talk battery voltage  on the two center pins of the ports?


PS: In the meantime I looked at some circuit diagrams.  It is puzzling that 3 ports would show 15V instead of 12.  It's easier to loose voltage, but to gain it is different.   If your measurements are correct, I think there must be something shorting the supply to the 18 V supply.

The system has essentially two power supply circuits, those two are protected with the those two fuses.  The two supplies generate a total of four voltages:   5 V, 12 V, 18 V, and 26 V.
26 volts is for the analog talk battery of the station ports.  It is also the DC that is superimposed while ringing. It makes it easier and quicker to detect the off-hook transition of the attached phone during the ringing cycle. The 26 volt supply also generates 18 V which seems used for relays and other switching circuits.
12 V runs the PT sets on each station port.  The 12 volt supply also generates 5 V to run the CMOS logic, CPU etc.