?

Hello,

I have a used IC-7000 and am concerned about the UHF FM transmit power.? I think it might have a problem now that I've tested it with a watt/SWR meter.

I know that the UHF spec is lower (35W), but it takes 80% RF power to get only 5W.? At 50% RF power I get about half a watt out.? To compare, it only takes 15% to get 5W on VHF FM? SWR is effectively 1:1 on both bands.

Is this normal or is something probably fried on the UHF side?

73,

Mike
K6MSM

On Fri, Mar 23, 2018 at 01:04 pm, <k6msm@...> wrote:

Thank you, both.? I will look into this.? Is it something I can replace with my unsteady hands or should I send to Icom?

Also, the ALC meter doesn't seem affected by changing mic gain on FM.? On 2m it's always too high (beyond the scale) and at 440 it's always 0.? Not sure if this is ok and/or related.

FYI at 100% power it only puts out 8W on 440.? I probably should dial back the RF % until I get it fixed to avoid further damage.

73,
Mike
K6MSM

The ALC meter acts differently on constant carrier modes like FM and RTTY.? A high reading on 2M is OK, being 0 on 440 means that since TX output power is too low the ALC circuit is not trying to reduce the IF gain to maintain the desired power.??

Replacing the UHF PA is relatively simple.? But getting to it takes a little work.? The driver board is soldered to the PA board, so it has to be unsoldered.? Make sure each pin wiggles before trying to remove the PA board, otherwise you may pull a plated-through hole out, which will have to be repaired.? The PA board has ribbon cables that attach it to the Main board.? Carefully pull them out and make sure the plastic stiffener on the back side remains? attached.? On older cables it often comes loose, in which case the cable should be replaced.? It centers the cable in the connector and assures the contacts are properly aligned.??

After the unit is back together you will need to do the TX Adjustments in section 4-4 of the Service Manual.? Specifically you must do:

1. DRIVE/FINAL IDLING CURRENT -- Step 1 &11 Final Idle Current (430M)
2. TX TOTAL GAIN -- Step 1 & 7 TX Total Gain (430M)
3. TX OUTPUT POWER (430MHZ) -- Steps 1-5.

For all of the above, read the section 4-1 and make sure you have the required equipment for the above steps and understand what to do.? If you are unsure about doing this type of work, send the unit to an authorized Service Center, such as the one in Michigan.??

The UHF PA is sensitive to voltage spikes greater than about 35 volts peak, which are often found on a vehicle's 14 VDC battery supply, due to the starter motor counter EMF when starting the engine.? Since I started using a Littelfuse TVS (transient voltage suppressor) in my mobile RigRunner Power Pole distribution units, I have had no further UHF PA failures in over 10 years.? There is a document in the Files section that describes how to add a TVS diode to a RigRunner to clamp the power spikes to a safe level.

Steve, W3AHL

On Sat, 24 Mar 2018 08:05:37 -0700, you wrote:

Replacing the UHF PA is relatively simple.? But getting to it takes a little work.? The driver board is soldered to the PA board, so it has to be unsoldered.?

No, you do NOT remove the PA board to replace the UHF transistor.
You have to remove the PA only for the driver.

Just remove two screws, unsolder the cover which is over the UHF
transistor, plug in the new one, screw&resolder the cover shield
and that's it. Takes 30 minutes.
No adjustments necessary, although it is ok to do with older IC7000
units because electrical parameters shift over time.
The adjustments are tricky and complicated,
better leave as is.
The main difficulty is to get exactly 3, 20 and 30 mVolt 1500 Hz
at the microphone input. Everything else is straightforward.
And you must provide exactly 13,8 Volt at the transceiver DC input
during transmit!

OE8UWW