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IFR COM-120B not charging internal battery

This forum exists for the purposes for discussing service monitors (This includes but is not limited to Motorola, HP, Aeroflex, GD, etc). Additional topics allowed include test procedures, interpretation of test results, where to find information about specific tests, antenna VSWR, return loss testing, duplexer and filter alignment, etc.

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AdrianH
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What radios do you own?: Yaesu FT-857, FT-902DM, FT70

IFR COM-120B not charging internal battery

Postby AdrianH » Tue May 08, 2018 10:55 pm

If anyone recognises the fault I would be grateful.

The unit runs OK on Mains, will work OK from the internal battery when charged externally, and will power from external DC. Just will not charge the internal battery.

So if anyone know the circuit enough to point me in the correct direction, not sure what the charging circuit could be, may even be a as simple as a limiting resistor or Transistor limiter etc. Diode etc but without circuits I hate just diving in blind.

Many thanks

Adrian

lc4600
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Re: IFR COM-120B not charging internal battery

Postby lc4600 » Wed May 16, 2018 1:07 pm

The 14 volt oven supply is used to charge the battery when the oven heat up current rolls off(R56-.43shunt and Q13-2N2907).Q13 will then turn on Q3(irf9540) and apply charge current to the battery thru CR16(mbr1645) blocking diode.
Carl N0PXJ

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AdrianH
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Joined: Fri Mar 16, 2018 12:03 pm
What radios do you own?: Yaesu FT-857, FT-902DM, FT70

Re: IFR COM-120B not charging internal battery

Postby AdrianH » Thu May 17, 2018 3:48 am

Thank you Carl I will have a look at mine and see if I can follow the line you mention.

Although I have to ask is the oven there if no option 2?, think I just have the standard 10 MHz, but it will give me something to look at.

Adrian

Jim202
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Re: IFR COM-120B not charging internal battery

Postby Jim202 » Thu May 17, 2018 4:23 am

The other possibility is the battery is old and has not longer any life left in it. One more possibility is the battery was left dead for too long of a time and you can no longer charge it.

I have played with rechargeable batteries for many years. Some can be brought back to life and others is like a dead horse. Once it's on the ground it will never get back up.

I use a variable voltage power supply and connect the battery to it. This way I can watch the voltage as well as the current. You will have to use a voltage above the battery voltage to get it to even start to take a charge. Normally the battery internal resistance is really high after it has been dead for any period of time. You have to get passed this to get it to charge.

Don't get the battery hot while trying to charge it. I generally have found that if you can get the current up to an amp or so, you might stand a chance to bring it back to life. But don't keep the current that high for any extended amount of time. Remember heat is the battery's worst enemy. Keep a close watch on the battery temp.

Once you can get any voltage to stay in the battery, now you can try to get it to provide some current. I have several resistive loads I have made up over the years. Sometimes just the 10 amp scale of my Fluke digital meter works well. I just put the meter in the 10 AMP. DC position and short the battery while watching the current. You will see the current slowly start to go up and then start to drop. Once you see the current start to drop, stop and go back to charging it.

If you can get the voltage up, you will need to use the resistive load, as more than a few cells working can cause damage to both the cells and the meter if the current gets above an amp or so.

Bottom line here is if the battery is old, you stand almost a zero chance of bringing it back to life. Get on Amazon and find a replacement.

Jim

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AdrianH
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Re: IFR COM-120B not charging internal battery

Postby AdrianH » Thu May 17, 2018 5:03 am

Hi Jim;

the battery is a new one I bought very recently as I knew the original was dead.

I will take the thing apart and look later.

Adrian

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AdrianH
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Re: IFR COM-120B not charging internal battery

Postby AdrianH » Thu May 17, 2018 2:21 pm

Well I have had a look and I am none the wiser, well perhaps I am. The PSU has been repaired in the past and seems to have replacement Electrolitics in it and a few replacement Tant's where the power connector is to the rest of the unit.

I found it very difficult to see markings on some of the components as the boards have been lacquered and there are no markings such as Q13 Q3 etc to determine which components are where?

I buzzed around with a meter and checked diodes etc then put it back together. On checking over the very limited information in the manual I noticed Connector 3 on the base of the PSU that should supply the Oven ( it does not have an oven fitted) and there is no 13.8 Volts to the socket J3 so I assume from Carl's information I would have to look as to why.

Not sure if you can power the PSU without the on off connections from the front so not sure at present how to go about this.

Carl if still reading at this point can you assist in anyway where I should look what components etc.

I took a couple of simple snaps with the phone, but not really going to show a lot.

Adrian

Image
Image
Image

I have virtually all sorted bar this now I know I can work without the battery but always a nice to have.

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AdrianH
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Re: IFR COM-120B not charging internal battery

Postby AdrianH » Tue Jun 05, 2018 10:09 am

Just an update, took the power supply out again, found an area on the board with some scorch marks, tested a few components and found a 30 Volt Zener dead short, it was in series with a standard style diode and used with T2 transformer and a LT1070CT switcher chip.

So both diodes have been replaced and I am awaiting a replacement chip to arrive, have also been testing caps around on the output from this. All seem OK so I can only hope I have found the issue.

I have also bought about 50 of the 4-40 UNC screws as there is a whole lot missing from around the PSU casing, so the test set has had some issues in the past with the PSU.

Fingers crossed that this will resolve the battery charging issue and I will have a fully functioning test set at the end of it.

I can but hope.

Adrian

lc4600
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Re: IFR COM-120B not charging internal battery

Postby lc4600 » Wed Jun 06, 2018 12:13 pm

Your on the right trail. Raw dc power is summed(CR10,CR11-MR502) with ext. dc, clamped(CR34-SA33a) and applied to pin 5 of U4(LT1070ct).The switched output of U4 pin4 beats on T2. The diodes from pin 4 to pin 5 of U4(CR31-1n4751)-(CR12 11DQ03) are the snubber for t2. T2 secondary is rectify by CR14(MUR860) and off to the races we go.
Carl N0PXJ

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AdrianH
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Re: IFR COM-120B not charging internal battery

Postby AdrianH » Fri Jun 08, 2018 2:40 pm

OK I need some guidance from anyone that knows,
New LT1070CT chip came today so all fitted back together, I hope I have not taken anything else out but on powering up the test set it gets part way through initialization and then shuts down.

I am hoping that as I have removed some shorted components that just perhaps, some voltages have lifted, being detected and shutting the set down?

This is the state of play.

With Mains connected but no internal battery connected, I am now getting 14.4 Volts to the battery terminals. I am getting 12.25 Volts at the High stab oven output. These are both with mains applied but the set not powered, just the orange light on at the front of the set.

On the mother board at the 24 pins shown in the cal document for checking voltages, obviously nothing on the listed supplies, but on Pin 11 there is 14.95 Volts. Pin 12 has 5.92 Volts and Pin 24 has 14.24 Volts.

Now unfortunately it has gone 23:30 hours here so continually testing and making beeps from the unit has to stop, so thought I would ask for advice for when I resume in the morning/afternoon. Is it possible I have lifted the supply rails by removing a short. Is there any better ideas/thoughts from the group, I would hate to over volt things and cause more damage?

Is there way to power the supply up out side of the test set to check voltages, or is it a waste of time as they will change under load to an extent anyway?

Cheers

Adrian

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AdrianH
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Re: IFR COM-120B not charging internal battery

Postby AdrianH » Sat Jun 09, 2018 6:22 am

OK just an update. The power supply still fails on mains, but when I run up on battery the unit initializes and passes self test. The boss at work made a comment about that was why the set was retired from service.

Strange it was working before I looked for the not charging problem, so either I have disturbed something or possibly a dry joint.

The unit will charge the battery when there is nothing switches on so wondering if an issue on the 300 Volt caps I can only guess at the moment that for some reason the DC from the bricks gives up and drop's off. There is a ribbon from the switcher boards that goes down to the relay board, I will make sure the connections are OK as well.

Adrian

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AdrianH
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Re: IFR COM-120B not charging internal battery

Postby AdrianH » Sat Jun 09, 2018 8:14 am

Well I've heard there was a secret chord
That David played and it pleased the Lord
But you don't really care for music, do you?
Well it goes like this:
The fourth, the fifth, the minor fall and the major lift
The baffled king composing Hallelujah

It was the 300 Volt caps one had broken it's solder joint to the board, and as I found out when I tried to remove still held a healthy voltage.

Neither of the caps where flush to the board and both had some movement in them, so taken out sort out some broken track, re-fitted flush, soldered and secured down with hot glue.

Back in working order, on mains and charging the battery.

Adrian


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