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Still without a power supply

Well… it has been some time since I posted my progress and even though I haven’t made any progress, sometimes just letting a problem simmer for awhile can help.

I you follow my excellent adventures I purchased a Ten-Tec Century 21 with a bad power supply and a sticky PTO.  The gentleman that I purchased it from certified that he had run it from an external power supply and until recently when I contacted Ten-Tec’s patient support guys I learned that it shouldn’t be run from an external power supply:

” Dear David:

The internal power supply has an over current shut down that protects the
final transistors. It is not a good idea to use any external power supply.
The switching supply will power the Century from the DC jack. It would be
best to repair the internal power supply.

Paul R. Clinton
Service Manager”

The trouble is I can’t find the problem.  I’ve gotten a generous suggestion to isolate the power supply by removing some the the leads to other sections and then test it but I can really figure out what is being said from the description… probably my general ignorance.

In any event I will be jumping back in with more questions soon, but life keeps getting in the way.

73 all!

Power OK from Transformer

Today was a day of slow movement on the C21.  I took a measurement from the secondary leads from the transformer to the power supply board and there is 19v AC or so coming off of that.  So with the supply from the transformer entirely within the 18v – 24 range I know that the transformer is OK.

The next step is to troubleshoot the components on the power supply circuit board.

Tomorrow I will look at the diodes to see if there is anything there to replace.

Sometimes it is just slow going, no two ways about it.

No power from the power supply

So you’ll see from the post below that I am still struggling with the mystery of the charred RCA jacks on the inside back of my  Ten- Tec Century 21. The pic above reflects some cleaning and examining I did today to try and figure out my next move.  If there is anyone out there that could compare my picture with their own unit, I would love to know if there is suppose to be any components where I have a gaping hole…

I did some DC reading from the IC1 on the power supply board and all the voltages where very low, somewhere below normal but still above the level of a “tripped” power supply.  I am not sure what all this means?  I got low readings on Q1 and Q2 as well.  Just what component is the cause I don’t know.  I do have a good book I think I’ll consult called “How to test nearly everything”, or something like that…  This will be a good lesson on how to troubleshoot.  I did buy this unit with an eye towards learning about HF rigs, after all this aged rig still is possible to troubleshoot, all of the components are through the hole.

I am also going to look into transformers, is it possible that they can go bad??  More to come…

Burnt offerings…

After considering which of the two problems I wanted to tackle first with my Ten-Tec Century 21 rig that I bought from KA9JBD on eBay I have decided to try and work on the non functioning external power supply.  I had a short talk with the John at Ten-Tec support,  John and all of Ten-Tec are very nice and patient so I am always glad when I can have some of their time.  First steps to check is that the 2 amp slow blow fuse is not blown and to see if there is 18v – 24 v out.

So I cracked the bottom of the case for the first time and had a rather interesting surprise,  just inside the back of the case behind the power cord and the jacks for external power was a large burn mark and a wired that looked melted off of it’s contact point.  At some point someone connected something that was a bit too much for the rig to handle.  The thing I can’t figure out is why the fuse isn’t blown, I put my multimeter on it with the continuity switch and got the friendly beep.  I could try buying another 2 amp slow-blow fuse to compare, perhaps it is the wrong size. Perhaps someone tried to replace it after the event and used the wrong size.

I’m not miffed by the discovery, but full disclosure would be nice to help troubleshoot – hey, that’s what “caveat emptor” is all about!

A journey of a thousand components starts with…

Ok,  I have to admit to being one of those city bound hams living in a high rise apartment building who is really only on UHF/VHF.  I like to build things and for the last year I’ve built two small transceiver kits, neither of which work at all yet.  I built the Rock-mite 40m from Small Wonder Labs and a DC 20 kit from Hendricks QRP Kits.

I do have a chicken/ egg sort of problem in that I don’t have a reliable antenna as I am looking to build something stealth, I don’t have any bench equipment unless you call a multi-meter equipment.  So naturally I’ve also got to admit that my budget is quite low as I have a family and kids who always have needs that come first.

After some questions on the forum over at eHam.net I decided that I wanted to acquire a Ten-Tec Century 21 model.  So I surfed the various site and bid and won a unit on eBay.  I know, never trust those guys right?  Well, I’ve been mostly lucky in the past and having a trust of hams that at least give their call sign in the description I went ahead anyway.

So now I’ve got this cute little (heavy) paperweight depending on my skills to bring it back to it’s glory days.

Today brings my adventure of new beginning in “boat anchors” and the promise of HF from my New York City apartment.

Stay tuned and 73 all!

de W2DAB