[TenTec] Jupiter 538

[Mike Bryce]

A long story short….

Years ago I purchased a Jupiter with black case, blue screen, that didn’t transmit. Easy fix! Right? Turned out I was wrong.

I got about 2ish watts on all bands. Suspected the finals. They turned out fine.

No drive! There were two 1/2 watt resistors near the driver transistor that were toast. Ha ha! Shorted transistor! It was, and I replaced it with a new device and new resistors.

Had 100W for a few minutes, the puff! No more driver transistor.

I worked on that radio for weeks, and wasn’t making any headroom. To repair that board, you need a jig to supply all the necessary signals, and to get to the bottom of the board for testing. I didn’t have said jig, so I swallowed my pride and sent it to Ten Tec to repair.

Several weeks go by and Paul Clinton, remember Paul from Ten Tec service? Informed me that the finals were bad. I told him I didn’t believe so, but since he was looking at the rig and I wasn’t to go ahead and fix the damn thing.

Then Ten Tec closed its doors!

So the radio sat for several months when I got a call from them asking if I wanted it fixed or returned, I said to fix it.

I don’t recall the name of the guy who called me to tell me the radio was done, but it was in fact the bad driver.

Now this is were it gets interesting. Apparently some where down the line, Ten Tec switched from a bipolar driver to a MOSFET driver, which was what I had. Then to add salt into the cut, the pcb wasn’t upgraded to the MOSFET design. I had a MOSFET driver in a board designed for BIPOLAR driver.

They (Ten Tec) fixed the radio, sent it back, and it lasted an hour before it stopped.

Returned the radio.

Weeks go by and finally, I get a call. Apparently the service tech tried a half dozed times to get the driver to stay together. He found out the MOSFET, in the bipolar pcb, would take off around 70mhz and cook itself. He offered me one more option, and that was to replace the entire pcb with a used bipolar board. I agreed and the radio has been making good power ever since.

It appears that somewhere they switched pcbs and mine was sort of caught between the change. I contacted the original owner and he said he always had problems with the transmitter.

I’’m not much of a fan of the Jupiter, they sound too digital to me, so I  hardly use it at all. I have noticed that due to lack of use, the rotary controls are very problematic. For right now, the radio is not worth my my time to tear apart and fix those controls.

73

Mike, WB8VGE
SunLight Energy Systems
The Heathkit Shop
http://www.theheathkitshop.com/
J e e p
o|||||||o 

A man with one clock knows what time it is. A man with two clocks is never sure.

> On Feb 18, 2023, at 7:00 AM, ROLAND HOWELL via TenTec <tentec at contesting.com> wrote:
> 
> 
> Further investigation on the PA devices fitted to the Jupiter, Q3/Q4 not sd1405 but MRF454S, drivers Q1/Q2 again not 2sc3133 but RD16HHFso the PA has been got at by previous owner, this is troubling somewhat.
> 
> FL2/FL3 have a white fur on the external surface, probably the same inside which is not good, have replacements on the way.
> 
> i have found a length of mini co-ax unsoldered at 1 end, it goes from term 19 on the power supply/ancillary board fitted to the back panel to PCB U7 but that end is disconnected, looking at the pins it seems to fit on RX-OUT, thats the 1 that has extra solder on it.
> 
> Thanks to Bob K4 for clarifying the output devices for me.
> 
> Snowy G0HZE
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