delara news Delaware Amateur Radio Association, Delaware OH   VOL 36 NUMBER 12

Craig

Craig MIller  W8CR

Don’t Give Up on an Old Friend

It started a few weeks ago.  I’d smash down on the PTT, push-to-talk, pedal on my ol’ reliable Yaesu FT1000MP MKV transceiver and noticed something wasn’t right.  The bar graph display in the upper left corner of the face panel that shows SWR and power output both went full scale with no transmit RF power output at all.  I checked the antenna connections, pushed various buttons, scratched my head – nothing worked.  After a about 10 seconds, I noticed the receive audio increased, that was interesting.  So, I pressed the PTT and all is well – transmitted just fine.  Well that was curious.  Ran fine the entire day. A few days later it happened again, same symptoms.  I wiggle more stuff, even smacked the top of the radio (smacking is an approved form of diagnostics/repair method by the CRRS, Clueless Radio Repair Society).  30 seconds later, the audio improved and everything was back to normal.  Close call.  This continued randomly over the next week.  I even left the radio on over 24 hours to see if it was something related to the power-up.  Sadly, whenever I’d hear the audio decrease, the unit failed to transmit, same full-scale reading on power and SWR. Then the day of reckoning arrived when it finally never recovered.  100% out of commission. NUTS! The symptoms kind of indicated there may be a problem with the T/R, transmit/receive, relay or circuitry.  Fortunately, I have the schematics so this should be easy to resolve. I have about 20 pages of squiggles similar to this one to go through.  This radio is one complex piece of electronics!  Forget it – I have no chance repairing this thing.  I don’t even want to open it up for fear of breaking something else.  I contacted the Yaesu repair center in California.  They were more then happy to inform me they no longer service this vintage, obsolete radio.  “What????!!!!!”  My precious MarkV that has ran flawlessly for 12+ years, solid as a rock for numerous Field Days, is obsolete? What a cold bucket of ice water dump on my head feeling.  They did recommend another outfit that may service it.  I did contact the other service business, they had a 4 week backlog, $75/hour bench time plus parts, if available and shipping on top of it all (heavy rig).  Reality setting in.  My poor baby may be relegated to the Rumpke trash dump or strip its carcass for parts and sell on eBay.  Time to buy a new SDR radio and join the Dark Side. I have a problem with a radio that requires Microsoft Windows to operate – that’s just wrong. With nothing to lose, I began surgery. This thing has layers upon layers of boards and modules and miles of cables and wires.  What a mess. I focused on the output stage, figuring there may be a lose connection or bad solder that could be the cause.  More wiggling and smacking.  Still nothing.  I broke out the voltmeter and started poking around.  I always like Yaesu radios, but their technical manuals could sure provide a bit more information on troubleshooting.  They label the wiring traces with odd-ball nomenclature like “STA” or “MD1” or “PRC”.  What the he!! does that mean?  Fortunately, some lines they actually give voltage values: 5, 9, 13, that’s helpful.  I snoop around checking voltages and notice a distinct lack of a -9VDC in certain circuits.  It was more like .352 VDC.  Hmmmmmm, I may be on to something.  I trace, using really strong reading glasses, the schematics back to the source of the -9VDC.  I find myself looking right a board, underneath the power-amp module, called the Reg Unit. I narrowed down to the culprit, there is a little component called a DC-DC converter that is responsible for the -9VDC line.  Either this part is shot, or one of the components around it bit the dust.  I applied the -9VDC to the radio from a bench power supply and everything came back to life! Well I’m in it now.  First thing I need is the proper equipment to replace these parts, so I picked up a re-work soldering station: I practiced on some boards I pulled out of miscellaneous electronic devices destined for the recycle bin to gain confidence before I burn up this board. Readers, I must leave you in suspenders.  I am still waiting on some of the components from Mouser so I can’t wrap up this article quite yet.  I am cautiously optimistic I’m on the right trail.  The money I (hope) saved added another cool tool to the bench and maybe I can get this classic back on the air! Fingers crossed….
© DELARA News, the official monthly newsletter of the Delaware Amateur Radio Association, Delaware, OH