Hi ..
Over the last two or three weeks i have noticed my TS 870 is taking
less current than usual.. maybe 13 amps, maybe 14 as far as i can tell ,
but never more .. .. so i and another local amateur tested the RF output
with a nice power meter / dummy load
The results were even across the board, 160 right up to 10m (my usual
haunt) any mode, except for AM of course, -
about 65w - 70w. everywhere.

I was doing research before i bought an '870 and a couple of people
mentioned the 870's generally dont give 100w,
but ck, its less than 3dB difference, but we tested the 870 2 years ago
when i bought it, and it was giving more RF out then,
it was drawing nearly 18A, and correspondingly more RF too, except that
it seems the PA is getting weaker.

My main use for the radio is local chatting on 10m FM 90% of the time at
lowest power, strangely when on full power i got occasional fuse blows..
though i know not to waffle on 100w FM, though the 870 spec and users
report its ok to do so for about a hour.
i cont fancy trying that.
I phoned Kenwood UK shortly after i bought the set asking why they don't
give 100w, he said it depends on the load, of course, so no problem

Question, does anyone thing my PA is dying on the 870 ?
- it looks bad... although the thing works perfectly otherwise.

Mark.

Mark wrote:
Hi ..
Over the last two or three weeks i have noticed my TS 870 is taking
less current than usual.. maybe 13 amps, maybe 14 as far as i can tell ,
but never more .. .. so i and another local amateur tested the RF output
with a nice power meter / dummy load
The results were even across the board, 160 right up to 10m (my usual
haunt) any mode, except for AM of course, -
about 65w - 70w. everywhere.

I was doing research before i bought an '870 and a couple of people
mentioned the 870's generally dont give 100w,
but ck, its less than 3dB difference, but we tested the 870 2 years ago
when i bought it, and it was giving more RF out then,
it was drawing nearly 18A, and correspondingly more RF too, except that
it seems the PA is getting weaker.

My main use for the radio is local chatting on 10m FM 90% of the time at
lowest power, strangely when on full power i got occasional fuse blows..
though i know not to waffle on 100w FM, though the 870 spec and users
report its ok to do so for about a hour.

Have you tried resetting all the PA bias levels on the pots inside? You
might have an oxidized connection somewhere, possibly inside a pot, on a
connector pin or a crimp, even a cracked solder joint that causes the
lower levels and the occasional burst of full power. I've seen similar
symptoms in other radios that went away after exercising (turn all the
way one direction, then all the way the other direction a few times with
the power off) related adjustment pots or finding a bad crimp or cracked
solder joint.

Hi Gwatts.. thanks for the quick post

No, i have'nt tchecked the PA bias or any pots for that matter- i shall
have a check around later.. i have the service manual and will study it
later on tonight .. the idea of twiddling pots worries me, i will
check all the connectors and stuff and get the magnifying glass /
voltmeter out later if the service manual makes sense to me
Thanks..
- Mark -

"Mark" wrote in message
...
Question, does anyone thing my PA is dying on the 870 ?
- it looks bad... although the thing works perfectly otherwise.

Mark.

Hi, Mark,

gwatts gave a very good suggestion. Several months back my 870 was doing the
same thing and it turned out to be that the negative lead of the power
supply cable was so badly oxidized that is was essentially an open circuit
and the rig was getting its negative connection to the power supply through
the ground on the back panel.

You need to check that power supply cable and the voltage drop across it and
see if it is in a similar condition. If that cable was ever used to connect
to a battery it may have turned black already and any splices, joints, or
connectors on it could be corroded and high resistance.

Regards,

Al W6LX

Hi Al.. and Thanks for the reply...
interesting answers coming my way.. what a great radio it is, but i
read 'all' the postings on this NG last night,
and it was interesting.

The supply cable is in very good condition, far as i can tell, but i
will peel back the black PVC bit on the radio end tonight,
and also check inside. the crappy CB quality fuse holders were hot
last time i attempted 100w FM,
they were glowing once on my old FT 890 AT radio - the PSU seemed to
cope with that set.
there are 3 or 4 clip-on ferrite's on the 870's DC cable already - which
is nice.

i don't have a ground here, i am on the 3rd storey, so a non-inductive
ground would be pretty tricky to organize.
and 99% of my QSO's are local rag chews on 10m anyway. but i will bond
to the cold water system this evening, but i know that may be next to
useless here.
The voltage drop at the PSU terminals is, of course 0.2 of a volt or so,
not really worth mentioning - but if i take the lid off the 870
later i guess i should be able to check for any drop inside the TRX. i
may also just 'build up' around the fuse holders with solder too,
this may help. seems the PSU lead is clean, the guy i bought the 870 off
of was using a PSU too. its a 2001/2002 serial 870 too.
i did fit another 4ft of red/black 25A DC cable via HD connectors
earlier this year, but didn't keep them on long, though it seemed ok.
i guess i need to test the cable under load.
last night on 10m FM i got the PSU supplying 15A - 16A which i guess is
on for 10m, but depending on the ATU / load it usually
draws approx 10A no matter what. strange. 14A - 70w ish on a dummy load
seems a little low, i guess i should use a amp..
but on 10m i will keep doing tests, my next test may be to take the
set to a friends QTH and use his PSU / ant..

Thanks Al. and Gwatts -
i shall do more digging
Mark

In article ,
Mark wrote:

Question, does anyone thing my PA is dying on the 870 ?
- it looks bad... although the thing works perfectly otherwise.

Mark-

Assuming you have solid state finals, your power supply voltage may have
fallen off slightly. I've found that a slight change in DC voltage
produces a large change in power output and power supply current. Be
sure your supply voltage is a solid 13.8 volts under load.

If you have the ability to measure the voltage inside the radio under
load, you can tell if there is a problem between the radio and the power
supply.

Fred
K4DII