This is a response to your requests for further information on the "surge protector diode"
problem. I will honestly say that I love the TS-870 and think it is an amazing radio. Following 
my post to this group, I received a significant number of responses indicating that surely this  
problem is real. A Kenwood service representative denies any such problem exists, more on that  
later. 
First of all, there are two levels and types of protection built into the TS-870. The first is  
"surge supressor diodes". There are two of them, D301 and D302. They are both the same and have a 
Kenwood part number of DSA301LA. These diodes are supposed to protect the front end components  
against the type of surges induced by electrical atmospheric disturbances (thunder storms). There 
is one across the 'antenna one' circuit and the other is across the 'antenna two' circuit. 
When they encounter sufficient voltage from your antenna they go to a lower resistance state and  
hold that value. An interesting way to test your antenna system in to connect a NE-51 neon  
indicator bulb directly across your coax the next time a storm is within 50 miles of your  
location. Watch the bulb! The diodes effectively kills the voltage spike but since it does not  
recover from this event, it kills the sensitivity of your receiver until it is replaced or  
removed from the radio. Normally I would say that this is a good feature. In this case, it  
happens so often that it cannot be considered appropriate. Since it is a "wired in" component it  
is not elementary to replace, which means your radio needs service! 
Second there is a pair of lamps, PL1 and PL2, in the RF Unit. These lamps are to protect the  
receiver from high levels of RF being induced into the front of the TS-870. The typical condition  
that would cause this is having a mobile station, capable of several hundred watts, pull into  
your driveway and key up right under your antenna! That would cause these devices to open and  
your receiver would hear about the same as a red clay brick! The Kenwood part number for these  
little buggers is B30-2134-05. To change these you must remove the RF Unit from the radio and  
unsolder these and replace them. This is again a costly repair! 
You can easily order these parts yourself from East Coast Parts at 800-637-0388. They are open  
from 9:00 AM until 5:30 PM waiting for your call. 
Now the SAD part! Several months ago I was sitting listening to 75 meters and noticed that the  
ol' 870 just didn't have the spark that it used to. I had noticed this earlier but sort of passed  
it off as maybe a bad antenna or bad band conditions. I received an email from a friend and much  
to my horror he brought the whole thing to immediate light. His email was simple, asking me if my  
TS-870 just wasn't hearing as well as it used to. Apparently his had the same problem! 
A little investigating under the covers revealed the real truth. These diodes, little glass  
encapsulated blobs, had turned blackish, sort of like a fuse that had blown. My friend had his  
replaced and immediately decided that an Icom 756 Pro would be put in place to solve his 870  
problem. He had two TS-870's and both of his had this same problem.  
My TS-870 is an 8 million serial number unit. I saw another, higher serial, unit for sale and 
bought it as a sort of upgrade. It was 2nd day air shipped from Fairbanks Alaska and guess what, 
it had the same problem. I first confirmed this with my HP8640B signal generator. I clipped the 
diodes completely out of one unit just to check the diagnosis and BINGO the problem was fixed! Of 
course, the receiver would be without "surge protection" if I put it back on the antenna.
I contacted Leo Fahmie of Kenwood Amateur customer service with my problem. He was adamant that 
the TS-870 didn't have such a problem. He claimed to have checked with their parts department to 
see if there had been a run on these diodes. He has been with Kenwood Amateur support for four 
years and claims that he has never heard of such a problem. I would not really like to publish 
his email without his permission but roughly he says that .. there are no circuit changes and no 
design flaws in the TS-870S meaning that no one is having a design problem with this unit. Let's 
just say that those are his exact words without quote marks but I could have put the quote marks  
in! 
There you have it. You now can look at your 870 and determine if you have the same problem and  
you have enough information to order the parts and fix it.
 
Larry W9MDX