HT600 power amp problem

[eleet]

Hi fellows,

I have a VHF HT600 with an intermittent problem with the power amplifier. The output power is low, but intermittently normal. I found this out after I adjusted C120 for output vs. current draw and put the radio back together.

I want to see if you guys know of any common problems (cold solder? flaky passives?) with the unit before I get to step 4 of the standard motorola troubleshooting process:

1. Key the radio up and smack it
results: power level is momentarily what it should be at the instant the radio receives impact

2. Key the radio up and shake it
results: power level alternates between low and normal with the shaking.

3. Take it apart and poke around with a diddle stick, then stop and ask for help
results: i did not find that applying pressure to any part of the board or any component i could reach with the controller still attached made any significant difference. i noticed that the area between Q104 and C120 on the RF board gets exteremely hot, so i stopped this game.

4. unfold the schematic, take measurements, and find the problem the proper way. hey what is this flowchart on page 31?

Since you guys have lots of great realworld experience and the manual is all about theory, I figured I'd ask. Plus I don't have a "flex extender fixture!" I just can't bear to salvage what could be a good radio for parts.

[MTS2000des]

have you inspected the antenna ferrule coming from the control top to the RF board? this is a known issue with Genesis radios. Sometimes they literally disintegrate or develop a cold joint. Usually close visual inspection will show it to be cracked just enough where it causes an intermittent connection.

[eleet]

Thank you very much!

Looking closely, the problem is obvious. This was too small to 'jump out' at me. Now it all makes sense.




Reflowed here and added a little solder. Now the radio should be good for another fifteen years of swinging it around by its antenna. I'll start tonight!

[MTS2000des]

knew it! glad that's all it was. every single HT600 and MT1000 I have ever owned (especially the red board one like you have) has had that exact problem. I think it is oxidizes and separates over time. I got a whole box of VHF HT600's from a gov't auction once and they all could RX but TX was piss poor and that was the problem with all of them.

[indigo]

Indeed, I have seen this problem fairly often - every unit I handle is checked for this, and several have been resuscitated as such...

Had an MT 1000 with this problem recently that also exhibeted poor sens on receive - once this joint was reflowed the unit was christened as practically brand new.

Matter of fact, should it be said that when handling used or decommissioned Genesis equipment, that this joint, among other things, should as a rule of thumb ALWAYS be examined BEFORE testing the radio in transmit (or selling it!) for so to not blow pa (or blow your rep with your buyer?!)?

Any others out there have any success (or horror?) stories re. this Genesis problem? Any other suggestions on what to AVOID when performing this 'repair'?

Incidentally, as quality goes I still agree that the Genesis stuff, particularly the MT1000, was/is/always will be one of the all-time big-/\/\ greats, and this particular board solder stress joint is not typical of only /\/\ Genesis rigs, but other manufacturers as well (i.e. I just remedied an ICOM ICH-16 land mobile in this fashion and it's as if the unit was electrically brand new now, alas, at least for the time being......that thing occasionally gets beat up in the field.....)

[wavetar]

Indeed, any radio which has a similar solid antenna connection suffers from the same problem, be it Motorola, Kenwood, etc. It is the one real design flaw in the HT600/MT1000 series. If not for that, the radios would almost never need repair. As it is, heavy users need it fixed every year or two.

The 800MHz Genesis series (MTX800/810/820) had a flex cable going to the board, which eliminated this.

Todd