PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

[sententia]

Hello everyone,
I have this Panasonic KX-TD1232CE Digital Hybrid telephone system which has a problem with the dial tone. The problem is that during the "silent" part of the dial tone, in internal calls, there is a very harsh sound.

The system is very complex for my knowledge to even figure out where the problem might be. I had an initial check some months ago on it but did not find any solution. I did check the power supply which seemed to be working fine.

The system has 16 extensions plus an external board that adds 8 more (KX-TD174).
I doubt that the problem is with the CPU as the problem appear initially on the internal extensions and after few months on the add on extension board.

Capacitors did have a high ESR but i don't know if that could cause such a problem. Is it possible that the harsh sound is from a DC block capacitor not working?

I attached a recording in order to hear the problem. TURN DOWN the volume before listening! (it is in .zip format / .wav not allowed)

This weekend i will remove just the extension add on card to do some further component testing. Unfortunately because the PBX is online i have very limited time for debugging (only weekends mainly).

I have included service manual and some supplement manuals.

Any suggestions are really appreciated!
Thanks!

P.S. The PBX has another problem. After some power failures the internal analog CO line are dead and always come with busy dial tone. Now we only use the ISDN extension card. I don't think the problems are connected.

[sententia]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

for some reason i get internal error trying to upload all files.
Here is schematic diagram.

[kasfamily]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

Reset you done?

[sententia]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

Thanks for reply.
Yes i have tried a full reset without any luck. It didn't make any difference..

[dj_ricoh]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

Thanks for reply.
Yes i have tried a full reset without any luck. It didn't make any difference..

i was wondering if the noise come only from this terminal or all the clients have this noise on the line.

do you have a central box where all the phones go?

nvm did not finish my coffe uff

[dj_ricoh]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

i think the only way is to actually take the psu out and de flee it from any dust and triple check every cap and the rest for leak

[sententia]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

Yes all extensions have the same problem.
First it appeared on all 16 internal extensions and after a while on the 8 extra extensions add on card.

Yes all clients connect with a 50-pin connector plug (for each 8 ext group) from PBX to telephone block terminal box.

Some time ago i did took out PSU, cleaned it and tested some capacitors and output voltages. Everything measured OK with a DMM. I don't have an oscilloscope to do further testing.

Do you think the problem is with the PSU?

Thanks.

[kasfamily]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

Very dirty - it is need to clean all the boards, vacuum or blow of the compressor.

[sententia]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

These photos were taken before cleaning and removing the PSU.
I may manage to get the pbx today in order to take some more detailed photos and perform some further tests.

[stj]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

take the top boards out so we can see under them.

and recap the psu, it's a bad design putting caps against heatsinks, it reminds me of old VCR's
use good parts like panasonic FR
and check the soldering for cracks on it too.

and while your in there - check the voltage on the yellow lithium battery on the cpu board.

[sententia]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

Yesterday i managed to get the PBX from a few hours and perform some tests.
I am now positive that the PSU is working OK as all capacitors (except 2) were in top condition (Panasonic HFG). I replaced 1 10uf with high ESR and i found one 330uf that measured 310uf.
I did replace some capacitors i found with high esr or low capacitance on CPU and EXT board, but they were not the cause of problem.
I don't know about the big green 0.47F 5.5V capacitor as i tried to measure it off board but didn't get any reading. But i doubt that is the cause of the problem.
Maybe a look at schematic might help as to were signal are generated etc.

Yellow lithium battery checks OK.

More photos as well.

[redwire]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

Black dust usually has carbon, from coal or charcoal and is slightly conductive. You have to clean that off.

If the problem is in a bunch of channels, I would check the power supply voltages (three of +5V), +15V, -15V, -5V etc. (I could not open the .RAR files they have an error on the .pdf's in 7-Zip). That's at least 6 voltages to check.

The unit also needs a dedicated earth-ground connection, there should be a separate wire for that. Otherwise, you get problems with the trunk lines as the CO is referenced to earth ground.

Usually a problem with one line is due to worn relay contacts. You can tap on them and see if it can go off-hook or if audio gets better (on the analog trunk lines).

[stj]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

the big green cap is a double-insulated / silver / super cap.
.47f is 470,000 uf - out of range of most meters.
it's used as a backup for the ram together with the yellow lithium battery.

[stj]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

you need to resolder cn401 & cn402 btw.

[sententia]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

redwire,

I did some cleaning when i removed the boards, with vacuum cleaner, but since i didn't have much time i didn't do a thorough clean with the compressor.

The problem with the CO lines is separate from the problem with the EXT dial tone. The CO lines were broken instantly after a high voltage in analog tel lines (i think or something similar). ? I have another PBX with the same problem.
Anyway since we only use the ISDN expansion this is not a problem at the moment i think they are not connected.

I have checked the voltage outputs of the PSU and all are within the service manual range.

Now about the earth connection. There is always an earth connection through the power plug. All other earth connections interconnect within the box. I remember installation manual states to have a second earth from pbx side pad, but i think it is for extra safety.

When the PBX powers on the relays on the CO board do a "cycle" or it sounds like that at least. I think relays are good.

stj, i know about the big cap. Checked my meter and is up to 0.2F. However when i test an identical cap on the DISA card (on circuit) i got a "CELL" reading from meter and not open circuit.

I lost you about desoldering the CNs. That is a separate bus board with all the plugs.

[sententia]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

I combined some schematic diagrams from service manual for easier viewing..

[stj]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

cn401& 402 on psu have bad soldering.

[kasfamily]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

Necessary to verify compliance with waveform generator and the power bus IC19

[stj]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

256k eprom,
unless it's got the checksum printed on the label, it's gonna be hard to check.

[Longbow]

Re: PANASONIC KX-TD1232 CE - PBX hybrid - Dial tone problem

sententia,
You have a lot of money tied up in your phone equipment and you are relying on it for your business. Up until now everyone is just guessing. It is time to use a good oscilloscope and signal generator to do some serious troubleshooting. Having 2 systems to work with should speed up the repair, but some solid information is needed first. Surely the service manual has a troubleshooting flow chart and block diagrams? That's where I would start.

Thanks for posting the noise file. Very interesting. Did this noise appear suddenly, or did it gradually increase over time? Scope the digital line coming into an extension phone and see what type of signal is present there. If a phone has an unused extension button, is the static noise still present?

It seems like you describe a failure due to a local power interruption or power fault. If so, you have a good place to start looking. Is there a block labeled "distribution interface" or something similar? Take a phone and plug it into the PBX at the equipment room itself, preferably before the distribution section. Same problem?

As far as grounding - this is important. The main equipment room should have a large copper grounding bus. Each piece of gear should be connected to the bus, and the bus should then be grounded to the building earth ground at the electrical panel. Of course, we have to keep in mind that the present arrangement was working without noise for some time previously. Still, the ground bus should be installed in any case.