After receiving an e-mail from Jan, DG3FDM (thanks, Jan!), who points out a mistake I made with the position of the anti-parasitic resistor on the PCB (it's only in the DC bias path at the point I connected it, since the RF signal comes from the other side of the PCB, after the PCB position I indicated - the schematic is OK though), I think it's time to present the latest information I have since gathered on the matter.
After observing the behaviour of the IC-7000s I have performed the mods on for some time, I think I have finally spotted the true reason for the malfunction, and apparently it is NOT the suspected parasitic oscillation of the DRIVER unit!
Let me explain: After performing the second part of the "stabilising" mods (16 March 2010), that IC-7000 disappointingly blew the driver again in about 15 days. Then, after again replacing the driver, I also installed the heat sinks on the pre-driver and pre-pre-driver transistors, which I noticed that became extremely hot after pressing the PTT for a few seconds (and then I posted the "last" 7000 mods, on April 23rd).
That particular IC-7000 has been in constant use on all bands since then, without any more problems. It had quickly blown the driver transistor three times before the installation of the heat sinks!
There is also more evidence coming from my FT-817, which also stopped blowing the (MOSFET) final amplifier only after I simultaneously installed similar improvised heat sinks on the (also terribly overheating) DRIVER transistors, along with the anti-parasitic resistors!! I have concluded that the heat sinks solved the problem, NOT the anti-parasitic resistors! (I had included the heat sink mod in the FT-817 paper in www.mods.dk, of course without recognizing its importance then, I just thought it would be nice to cool those poor flaming transistors).
So there is very strong evidence that the anti - parasitic resistors and other such measures are actually not needed, the overheated pre-driver transistors caused the problem in both the IC-7000 and the FT-817 (and perhaps in many more transceivers with overheating driver and pre-driver stages)!
With the pre-driver heat sinks, the problem seems to have immediately stopped for good in both transceivers (my 817 has been working OK for more than 18 months now, in mostly portable operation).
So, please install the heat sinks only. The other anti-parasitic mods don't hurt the transceiver in any way, on the contrary, they may remain in place if already performed, but my current results show that the only mod that needs to be done is that of the heat sinks on the severely overheating pre-drivers.
In just a few words, do ONLY the heat sink mod of the 23rd April 2010 post! The other mods don't hurt anything, but apparently they are not needed. (However, if you have already done them, just leave them in place!)
After observing the behaviour of the IC-7000s I have performed the mods on for some time, I think I have finally spotted the true reason for the malfunction, and apparently it is NOT the suspected parasitic oscillation of the DRIVER unit!
Let me explain: After performing the second part of the "stabilising" mods (16 March 2010), that IC-7000 disappointingly blew the driver again in about 15 days. Then, after again replacing the driver, I also installed the heat sinks on the pre-driver and pre-pre-driver transistors, which I noticed that became extremely hot after pressing the PTT for a few seconds (and then I posted the "last" 7000 mods, on April 23rd).
That particular IC-7000 has been in constant use on all bands since then, without any more problems. It had quickly blown the driver transistor three times before the installation of the heat sinks!
There is also more evidence coming from my FT-817, which also stopped blowing the (MOSFET) final amplifier only after I simultaneously installed similar improvised heat sinks on the (also terribly overheating) DRIVER transistors, along with the anti-parasitic resistors!! I have concluded that the heat sinks solved the problem, NOT the anti-parasitic resistors! (I had included the heat sink mod in the FT-817 paper in www.mods.dk, of course without recognizing its importance then, I just thought it would be nice to cool those poor flaming transistors).
So there is very strong evidence that the anti - parasitic resistors and other such measures are actually not needed, the overheated pre-driver transistors caused the problem in both the IC-7000 and the FT-817 (and perhaps in many more transceivers with overheating driver and pre-driver stages)!
With the pre-driver heat sinks, the problem seems to have immediately stopped for good in both transceivers (my 817 has been working OK for more than 18 months now, in mostly portable operation).
So, please install the heat sinks only. The other anti-parasitic mods don't hurt the transceiver in any way, on the contrary, they may remain in place if already performed, but my current results show that the only mod that needs to be done is that of the heat sinks on the severely overheating pre-drivers.
