JI1FGX/DU9 Philippines Mindanao Island ICOM IC-820H PLL UNLOCK Repair (2025/10/09)

JI1FGX/DU9 Amateur Radio Diary, Mindanao, Philippines, IOTA OC-130.

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25/10/12	Received APRS signals from ISS
25/10/11	TNC software for APRS manual
25/10/10	TNC software for APRSVer1.0
25/10/09	Making myopia glasses
25/10/09	ICOM IC-820H PLL UNLOCK repair
25/10/05	435MHz Cross Yagi antenna production preparation
25/10/04	Receiving SSTV from the International Space Station
25/10/03	Repair of elevation rotator KR-500
25/10/02	145MHz Cross Yagi antenna production preparation
25/10/01	received APRS signal from ISS
25/09/29	CQ WW RTTY contest
25/09/27	SSTV from the ISS
25/09/26	WARC band fan-out antenna
25/09/25	levation rotator KR-500 acquired
25/09/23	APRS TNC software Dire Wolf with Hamlib
25/09/23	TNC software direwolf
25/09/21	Russian satellite RS-44 beacon
25/09/20	Installing a radio in a car
25/09/17	DH1NGP Peter radio vehicle
25/09/13	3.5MHz SWR increased
25/09/12	3.5MHz Zepp antenna adjustment
25/09/10	Geostationary satellite QO-100
25/09/09	Preparing for the satellite station
25/09/08	DU9JJY satellite station
25/09/07	14MHz late at night
25/09/03	Mitsubishi Strada Pickup Truck Oil Change
25/08/18	WSJT-X Automatic operation Ver0.1.0
25/08/18	JTDX Autonomous operation Program Ver0.6.3
25/08/10	Software List

25/07/26	AutoCWType_Ver1.5.8
25/07/20	Create one month's worth of ADIF files from JTDX Ver 2.6.5
25/07/19	Japan's Radio Wave Usage Tax
25/07/13	IARU HF Contest
25/07/10	Software updates
25/07/08	DXV500ZS linear amplifier repair
25/07/07	CQ Machine Program
25/06/21	LoTW system upgrade
25/06/18	RG8 for 3.5MHz arrived
25/06/15	Time setting Ver0.5
25/06/14	Drone Habsan ZINO arrives
25/06/12	Philippine Independence Day
25/06/11	Algeria 7X2RF QSL card.
25/06/10	Translation API Program
25/06/09	DXCC150 award certificate arrived
25/06/08	AutoCWType_Ver1.4.1
25/06/07	Introducing the Shack
25/06/06	A portrait drawn by ChatGPT.
25/05/26	Windows full-width/half-width switching.
25/05/17	OK2ZAW BCD to 16 converter.
25/05/16	For 3.5MHz Zepp antenna. Stepping motors
25/05/15	3.5MHz stepping motor design.
25/05/14	3.5MHz tuning coil installed.
25/05/11	3.5MHz antenna installation completed.
25/05/03	JTDX Autonomous Driving Program Ver0.4.3.
25/04/26	Drone Habsan ZINO.
25/04/25	Time setting Ver0.3.
25/04/24	AutoCWType_Ver1.3.
25/04/23	Preparing for FTDX3000 LCD repair.
25/04/22	Installation plan for 3.5MHz Zepp antenna.
25/04/21	AutoCWType_Ver1.1.
25/04/20	10,14MHz antenna installation completed.
25/04/19	JTDX Autonomous Driving Program Ver0.4.1.
25/04/19	14MHz antenna pole installed.
25/04/18	ThinkPad X390 repair completed.
25/04/17	Search is now possible.
25/04/15	Preparing the 10MHz dipole.
25/04/12	Hexbeam Part8.
25/04/06	My ThinkPad X390 is broken.
25/04/05.	Time setting program.
25/03/31	JTDX Autonomous Driving Program.
25/03/30	Automatic log sending from CWType to Hamlog.
25/03/21	Hexbeam Part 7.
25/03/20	FreeDV Part 3 First QSO.
25/03/18	FreeDV Part 2 QSO in the shack.
25/03/16	Hexbeam Part 6.
25/03/15	Install FreeDV Part1.
25/03/09	Hexbeam Part5.
25/03/07	Hexbeam Part 4.
25/03/05	28MHz antenna modification
25/03/01	FTDX3000 is broken!
25/02/28	Pileup at 50MHz FT8.
25/02/28	DXV500ZS linear amplifier repair.
25/02/27	Tower pipe rebuilding plan.
25/02/26	Direction to Japan from Ozamiz.
25/02/26	28MHz is not available.
25/02/23	DXV500ZS linear amplifier repair.
25/02/22	Hexbeam Part 3
25/02/21	Hexbeam Part 2
25/02/18	28MHz antenna construction.
25/02/17	18,24MHz antenna height construction.
25/02/16	Z26NS Cosovo.
25/02/14	21MHz FT8
25/02/12	7,21MHz antenna repair.
25/02/08	Operating CW at 21MHz.
25/02/05	DXV500ZS linear amplifier failure.
25/01/19	Input Director.
25/01/14	Temporary license renewal.

ICOM IC-820H PLL UNLOCK repair (2025/10/09)

ICOM IC-820H, acquired from DU9JJY for satellite communications.
However, after about 5 minutes of turning on the power,
the frequency display showed both VHF and UHF '-------' and the PLL was in an UNLOCK state.
It will return to normal in about 5 to 10 minutes and then you can use it normally.

However, if you turn off the power, wait for it to cool down, and then turn it on again, it will return to the same PLL UNLOCK state.

What I did this time
0) When ICOM IC-820H is turned on, the PLL becomes UNLOCK for about 5 minutes. It returns to normal after 5 to 10 minutes.
1) Fixing the symptoms by disassembling the case
2) Put the case back together and try to reproduce the symptoms. Confirm that the PLL lock is fixed in about 5 minutes.
3) 30.2MHz PLL/DDS reference oscillator X1 is suspected to be faulty and checked with an oscilloscope.
4) Confirm that the PLL lock is released when the output of X1 is grounded.
5) At this point, I suspect a defect in the X1.
6) However, even if you warm up the PLL circuit of X1 or V/UFH with a hair dryer, the PLL lock remains unlocked.
7) Reassemble the case and check that the PLL is locked after about 5 minutes.
8) I tried heating the IF board in order with a hair dryer and found that the PLL locked when I heated the circuit called MP1.
9) Cool each part of the MP1 (small regulator/power module) with cooling spray.
Confirmed that 10uF and 47uF electrolytic capacitors are effective for PLL unlock
10) I confirmed that the PLL unlock function improved when I replaced
the 33uF electrolytic capacitors I had with 10uF and two 33uF capacitors with 47uF.
11) I bought a 16V 100μF from an electrical parts shop in Ozamiz and completed the repair.

I searched for a PLL unit but couldn't find one.
ChatGPTChatGP found the service manual and when I checked it, it said 'Remove the MAIN unit'
So I took pictures of all the connectors connected to the main unit board,
removed them, and then removed the board, but the PLL unit did not come out.

By removing the four screws that secure the main unit, the PLL unit was revealed.

below.
PLL/DDS reference oscillator x1
VHF PLL circuit
UHF PLL circuit
VHF DDS circuit
UHF DDS circuit
There was

At first, I suspected a faulty oscillation in the reference oscillator X1.

Even after warming each unit with a hair dryer, the PLL does not lock and the frequency display remains abnormal.

If you leave the case off, the PLL will remain unlocked no matter how long you wait.
If you then put the case back in place, the PLL will lock in about 5 minutes and the frequency display will return to normal.
It was confirmed that the symptoms could be reproduced by repeatedly removing and replacing the case.
As a result of this test, I began to think that the problem might not be with the reference oscillator or the PLL unit.

However, it still transmits even when the PLL is unlocked.

I tried warming the main unit up little by little with a dryer.
Then, when I warmed up this MP1 unit, the frequency returned to normal.

According to ChatGPT, this appears to be a switching power supply for the PLL unit.
If I heat it with a hair dryer and then cool it with cooling spray, the frequency display becomes abnormal again.
Even if I heat it up again with a hair dryer and cool the IC, the frequency display remains normal.
Next, when the two capacitors are cooled, the frequency display becomes abnormal.

It looks like these two electrolytic capacitors are bad.

Tested the operation with a handheld electrolytic capacitor.

The PLL unlocking problem was fixed.

The Ozamiz electronic parts shop didn't sell surface mount electrolytic capacitors, so I bought a regular 100μF 16V electrolytic capacitor.

Replaced two electrolytic capacitors.
The right is 100μF 16V
The left is 47μF 16V

It's sticking out from the metal case, but that can't be helped.

Repair completed!
I'm grateful that there's a small electronic parts store in Ozamiz, Mindanao.
When I told the female owner of the store 'I love this UNITRUST', she seemed happy.

October 5, 2025. October 9, 2025.