Re: [IC-7000] My 7K won't power up


Steve W3AHL
 

Before you pull the PA board, there is something that doesn't seem right in your original description of the problem. I can't imagine a short circuit inside the radio pulling enough current to drop 13.8 VDC to 3 VDC at the radio without blowing the fuses.

I've seen several Astron power supplies that have a problem that causes their internal overvoltage protection circuit to foldback the output to about 3 VDC. The problem is often imtermittent and often happens when the radio is powered up. Sometimes this is caused by poor ground connections between the circuit board and chassis due to loose mounting screws. Adding star lock washers corrects this. Their are other causes of this false overvoltage foldback issue, also. This didn't seem to be your problem, since you said the power supply output remained at 13 volts.

As others have pointed out, the fuse holders on the 7K's power cable develop high voltage drops due to poor contact design that allow oxide buildup on the fuse blades to create excessive resistance. The solution is to replace the fuse holders with standard automotive style fuse holders or eleiminate the fuse holders if you use something like a RigRunner for DC distribution. Check the voltage across each fuse holder under load. It should be less than about 0.5 volts with a 20 amp load.

Pulling the PA board isn't trivial. You have to unscrew all FET's from the heatsinks (and usually redo the thermal compound when replacing them). The driver board has to be separated from the PA board, since it is screwed to the chassis also. Then remove the cable connections. Be careful with the ribbon cables from the main board to the PA at the front edge.

When checked with a DMM on diode check mode, a good 7K will read about 0.53 volts with black meter lead to red power cable and red meter lead to black power cable. It will slowly rise (as the caps charge) to about 1.6 VDC when the leads are reversed )black to black and red to red).

Steve, W3AHL

--- In ic7000@yahoogroups.com, "g3xjs" <barville@...> wrote:

Hi Steve

Many thanks for the info.

I will investigate those diodes further with a DMM but it looks like I might have to remove the PA board.

A quick look suggests that I will have to unsolder the two connections on each SO239, but I'm not sure what else needs to be disassembled before the board will lift.

Anybody have any clues/recommendations?

My thanks to all for their time and interest.

73 Peter G3XJS


--- In ic7000@yahoogroups.com, "Steve W3AHL" wrote:

D701 &702 are axial leaded diodes on the top side of the PA board at H70 V20.

Steve, W3AHL

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