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Panasonic KX-T30810 PSB rebuild help

Started by KennyCox, December 07, 2020, 01:03:28 PM

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I am new to the forum so first off let me say I am glad to be here and look forward to learning and contributing.

I have several rotary phones; mostly from 70's or later, and I recently bought a Panasonic KX-T30810 to use in my house so we could call from room to room, room to shop, ect.

Which is how I ended up here.

I bought the Panasonic KX-T30810 on fleabay and didn't even try to test it for months. No time. When I wasn't working right; So, I did what anyone would do; I dismembered it. My first thought was old/bad caps and I wasn't disappointed. I went looking for a service manual so I could get a schematic and found one here.

My problem is that I can't figure out which page in the manual connects to the left side page/drawing ( PAGE-18  "Schematic Drawing") of the Power Regulator board.

I have looked several times and can't figure out which page in the manual matches up to page-18.

Any help with that will be greatly appreciated!

Below I have posted some pictures for your viewing pleasure, showing what I found when I examined the PSB.

I have pretty much decided that I will have to replace all the caps and few other things.

Enjoy the pictures and I will post follow ups as I work on this.

Nice to meet you all!

There are no mistakes; only design changes.


Hello, and welcome to the nut hut...
It looks like someone let the factory smoke out of a couple tranny's.
The caps don't look too bad, but could always be refreshed.
Look on the main board too, to see if anything looks funny...SOMETHING took out the power supply.
or maybe just a surge?


Personally I am leaning towards moisture/corrosion and or leaking cap in at least one spot. In any event my goal at the moment is trying to figure out which pages in the manual match up to show the entire PSB!
There are no mistakes; only design changes.


This is Page -18 in the service manual. I can't figure out which other page matches up to this one. If anyone knows I would would be grateful.
EDIT #1:
            Sorry. I am blind. I looked closer at the manual and I was wrong. Page - 18 is not what I thought it was.
Pages 19-20, which I joined into one image below, is what I was looking for. So I have answered my own question.
Now, I will go through the PSB; remove all the offending parts; then put together a parts list for comment before I actually order.
Thank you.
Edit #2:
              Nope. I still think I am an idiot. Looking closer pages 19-20 don't look right either so I think I am back to square one.
I still need a complete schematic for the PSB....I can't figure this out.
There are no mistakes; only design changes.


Welcome to Forum - Page 18 is the correct one as I see F2 & F3, IC7 & IC8, etc. listed & are also on the board you are working on, which they are calling the "Power Regulator Board" - However, as you realized quite a bit of the schematic is missing & the rest of it does not seem to be included in the scanned KX-T30810 manual posted on the forum - Maybe someone more familiar with these will be able to provide the complete diagram.
In the meantime, I would definitely recap it and suggest you replace those components that look like they overheated or have any corrosion & see if that gets you anywhere - Good luck with it.


Thank you, and, yes; I am going to replace all the caps and may end up replacing most everything else!
I didn't think I was crazy when I looked at the schematic.....the manual clearly does not have the whole board showing!
There are no mistakes; only design changes.


So far I have replaced every capacitor on the PSB; one diode; 2 transistors and a couple of jumpers.
I have one diode that I suspect might be bad and need to look at it out of circuit to be sure.
I hooked everything up for a quick test and....still not working right buzzing in the audio now.
I can only get a phone to work on channels 14-18. By "work" I mean when I plug it in you can talk or blow into the phone and hear it in the ear piece. There is no dial tone....if there is supposed to be one. ( I have never owned one of these pbx's before)
Next I will test voltage output of every lead coming from the PSB and probably replace the one diode I think might be bad.
There are multiple other transistors on the board that i did not replace...they didn't look like they had any heat damage so I
left them in place.
After I get voltages tested I will post back and I guess go from there.
The one with all the arrows shows multiple transistors that I did not change out.
One picture with arrows shows transistors that looked like they got hot and I did change those out.
Another picture with an arrow shows the one diode I swapped out. The leg on one side was corroded off.
There are no mistakes; only design changes.


There are three cables coming from PSB to main board.
8 pin
7 pin
3 pin
The picture shows what I measured on all three.
I found some voltage showing even with power switched off on a few pins.
There are no mistakes; only design changes.


That stray voltage is probably the caps draining down.


Quote from: Key2871 on May 16, 2021, 06:04:13 PM
That stray voltage is probably the caps draining down.

. . . or possibly battery backup? Either an external battery or the newer huge board capacitor meant to hold programming code. Or are the power off voltages showing with battery backup defeated?


Things like this would have a super cap, one with a high fared value that was intended for exactly that porpoise to hold memory.
Instead of a battery or in some cases including a battery. Those fared caps hold a charge for quite a while but will eventually fade and memory would be lost.


Not to long ago and somewhere on the forum it was discovered that Panasonic stopped using the removable pig tail rechargeable externally mounted small battery and put a large capacitor on the internal circuit board for programming retention during power outages.

While the older external battery types could be removed from the PBX to restart the unit with factory RAM programming, the newer units meant a long power off discharge time to restart the PBX with factory RAM programming.

Point was if the voltage on the pins in power off, and power cord removed from the wall, could be "battery backup" power.

Question was does this 310 have a removable battery or a board mounted large value capacitor (and if so was it safely discharged before getting those power off readings?

If the removable battery was disconnected or a board mounted programming retention capacitor was fully discharged safely, does the 310 still show voltages at those few points?

The large green capacitors shown in the images above that look like the backup cap image posted some time ago. I can find that capacitor battery topic if wanted next time I am on my PC.


It's been some time since I read this battery/no battery topic

and briefly reading it now, it may be a permanently mounted internal rechargeable battery and/or a very large capacitor. unbeldi was a very credible member, he knew his stuff, and the entire battery discussion is informative.


IC 1,3,7 & 8, are all basic 3 leg regulators, and all should have a voltage present on pin 3. with power on
Those readings you took, that have .03, or .06, are prob wrong.
There should be more going on there. IMHO