FT7800 no power - dead or can be repaired?
Due to a failure of the power supply unit that converts 120vAC to 12vDC so I can use the radio in the house, my Yaesu FT7800 mobile radio received a higher voltage (20+vDC) than it's designed for (12vDC), and as a result it does not power on at all. Has this radio been fried beyond repair, or can I take it in to a shop (or do something myself if it only requires a simple repair) and have it fixed? If it can be fixed by a shop, any idea on how much that might cost? Need some input before I decide to go out and buy a new unit.
KE5LEH in rural New Mexico
There is no way of telling! I suspect one or more of the regulators failed. It could have zapped a final, but I sort of doubt that, although it might have gotten a filter cap of two. Just send it to Yaesu, and hope for the best!
You might want to invest in a power supply with an over-voltage crowbar built in.
Rural New Mexico? I'd call it the boonies, if it weren't for the fact the Lavender farm is close by.
The power is switched on by the CPU Q1065. If that part isn't working then you will never get a power on status. It could be the voltage being supplied to the CPU is missing or with overvoltage it just quit.
You can trace the circuits with the information available from; http://www.ko4bb.com/Manuals/Yaesu/Yaesu_FT-7800R.pdf.
Hope this helps
The over voltage will take out the first component that can not handle that electrical potential (E, measured in Volts). It likely can be repaired, but whether it is a simple diode, the CPU, or other components ... can only be determined on the repair bench.
Has this radio been fried beyond repair, or can I take it in to a shop (or do something myself if it only requires a simple repair) and have it fixed? If it can be fixed by a shop, any idea on how much that might cost?
Modern radios, since mid-1990s, largely use Surface Mount components and technology.
Reviews of Amateur Radio Equipment Repairs (companies & individuals)
Where did you buy radio? AES and HRO both have repair references.
Yaesu USA also has repair facilities in California.
You may want to contact Jim Smith W0MJY or Bob Campbell KC0LRT at
Burghardt Radio Repair in South Dakota --- that is doing full-time repairs.
You should expect to pay a fair wage to a US repair technician.
Many individuals are radio amateurs, and their hourly rates are less than you
would find at full-time component level repair facilities.
BTW, your local 13.8 VDC did not have Over-Voltage protection (20 VDC) ---
Use a Protector (West Mountain Radio's PWR Guard Plus, Mike Bryce, WB8VGE circuit for DIY Build) OR
DUMP that DC power supply !!
PWR Guard Plus, West Mountain Radio
The Protector, WB8VGE
Last edited by W9GB; 05-12-2012 at 03:17 PM.
We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths. -- Walt Disney
Open the rig, it's got a transient suppressor diode as the first component. It's a jesus diode -it dies for the rest of the thing to survive! Fails short, though, so the collateral damage depends on how fast the power has been cut off.
Go google the manual, follow the circuit and find the thing. Costs more to ship than the part itself. Can be fixed easily.
Looking at the schematic I see the power comes into the FT-7800 on TP1037. The transient suppressor is D1033 and it's supposed to trigger at 16.2Vdc. It could have shorted when the voltage passed that trigger, which is usually what happens, or it could have gone open. The voltage then goes to Q1043. The base of Q1043 is switch to a high state by the signal out of CPU Q1065. You probably by now have sent it out for repair but if you didn't then this is where to look. I also found other paths to components in the unit. The first thing you would need to do is restore the voltages that operate the rig. From there it's anybodies guess what else is bad.
Hope this helps
the TSD (D1033) are designed to fail short. So, for some few parts of a second, they short out the input, thereby protecting the load circuit. (Crowbar circuit) Then, if they absorb too much power, they melt down and fail shorting out the power in. This is the reason you need an adequately selected fuse in front. THis one will blow then.
'course it all depends on the voltages and the supplies internal resistance.
Anyhoo, i had the same same happen to my Ft-7800, they are easy to fix, and i rejoice they put in D1033!