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Thursday 2 August 2012

FT817 more investigation

More investigation.

There are two diodes (on my schematic) between the positive power pin and
the battery pack. It seems some newer units have an internal fuse, mine doesn't. Obviously either or both of the diodes (and/or the fuse) could have gone open circuit. I do not run my FT817 with batteries anyway. According to the circuit D1084, if it fails, would prevent operation on internal power (assuming no other damage). D1085, if it fails will prevent operation (and charging) on external power.

I will need to check the board which means some disassembly... the printed circuit traces (the techlab at work recommended checking them after I mentioned the problem) may also have melted.

The rather obvious failure I have seen of the T1035, a bifilar wound choke, the purpose of which is to isolate the external +ve from ground, is affected. Reading lots of group posts and it seems that some of the very early units (mine is August 2005) experienced catastrophic melt- down when insulation on this choke melted, allowing positive and negative supply leads to short together more or less permanently.

Sounds a bit like mine maybe?

My serial is 5G990117. Asked how can I work this out. The serial number has the form YMLLNNN where Y = the last digit of the year of manufacture, M is a letter representing the month of manufacture with "C" = January, "D" = February, and so on, the lot number is representated by the two digit LL (00 - 99), and NNNN (0001-9999) is the unit number within lot LL.

The only other thing I can find out from is that the voltage drop across T1035 is used.

18HF1-ICThis sets the maximum amount of current that the radio can draw when transmitting in the HF1 band (0.1-<2 .5=".5" across="across" and="and" by="by" current.="current." drop="drop" finals="finals" font="font" for="for" higher="higher" is="is" measured="measured" mhz.="mhz." monitoring="monitoring" nbsp="nbsp" of="of" one="one" overcurrent="overcurrent" protection="protection" radio="radio" s="s" t1035.="t1035." the="the" this="this" values="higher" voltage="voltage" windings="windings">
I guess the danger is that the 13.8V line is connected to the PA/Finals. J1015 on the main board diagram.

And in through J3003 on the final diagram.

That the choke melted was it because the finals had failed or due to something else. The main board ribbon connector J8008 and associated 13.8V tracks show no damage.

The radio was in RX mode only at the time so hoping it was not the finals.

Now to find time and do the disassemble.

I will have Clive M5CHH FT817 side by side for comparison as I run through this.

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