Kenowood TS-570DGE Repair - lets get started (and finished as it turns out!!)

So....

Got it home and found some time to have a closer look at it.

Sure enough, as described, everything works, but its as deaf as a post :( , the TX side is fine, giving 100W out, so that's good.

I'd already downloaded the workshop manual prior to bidding (to check what components I might need to check the circuit configuration - well its best to know what your in for isn't it :) ) and so knew where the front end components, protection diodes, bandpass filter switching diodes etc.

So removed top and bottom covers, as usual the bit I want (rx input etc) is on the 'bottom' of the radio !

I start the investigation, no obviously damaged components from the top, no smell (remember that the seller said he thought that some had transmitted into it by accident) of burnt or damaged components.

I test the protection diodes - all ok - good
I measure the switching diodes on the bandpass filters - to my surprise there are all - so a moral there never believe what you are told :)

I have a break and a think at this point, I had expected this to be the problem.

I decide that I will fall back to normal fault tracing, and so inject a strong signal into the aerial socket and start tracing.

Circuit is below for this area so you can see my work ;)

Partial TS-570DGE circuit - copyright Kenwood Communications

1 - Signal at the antenna connector on the board - yes  (CN1 above)

2 - Signal at  R2 - yes3- Signal at R2 end of L4 yes4 - Signal at tp4 - NO (!!!!!!!!)These test are a little tricky as everything is surface mount, but no real problems, so I decide to inject the 14.100Mhz signal into TP4.Result is an end stop signal on the radio.So L4 is at fault ? - remove from the PCB and yes its open circuit :) - fault number one. I temporarily jump out L4 and sure enough - receiver works perfectly, pre-amp fine, all looks great :)Whilst in this situation I give it a really good check out - seems to work perfectly, have a few short qso's all fine, so a suitable surface mount 0.25u inductor goes on the part list.Whilst checking it out I notice that the attenuator doesn't attenuate (!) , so I chase the circuit and discover that R1 (56R) is open circuit - I have a suitable surface mount resistor and so remove it and replace - Check again and now the attenuator works - result !I then check around the circuit testing voltages as per the  workshop manual - (BTW - I really like Kenwood / ICOM service manuals as the have really comprehensive voltage / voltage tables for TX and RX - Yaesu don't seem to - why is that ?)At this point I check again all the bandpass switching etc - all is fine, I notice however that on TX the voltage on the rx line should drop from ~10V to 0 - ie muting the rx line, but it doesn't - another fault.I remove the PCB (as Q2 is mounted under the board) and as I lift the board - what do I find ? a rather burnt Q2 - so its added to the component list for repair.So conclusion ? - well it must have had some RF into it I would have thought. my guess is that the attenuator was switched in and it took out the 56R resistor, then the inductor and then Q2, thankfully it was transient and so no further damage was done.Components ordered, arrived and a pleasurable 10 minute install of the inductor L4 (if you should do this watch the soldering iron on the relay !!!, then removed the board and replace Q2.Re-assemble it all, check and check again - all works perfectly.I then do a full alignment check as per the workshop manual, everything is spot on, nothing to adjust or change.I then spend a little time cleaning it up a little and then a very pleasant afternoon on 40M and 18M having so very pleasant QSO's - all works perfectly.So the conclusion;Yes there was some damage, someone (or something) did take out some front end components but whatever it was must have been pretty short lived as none of the normal protection components or bandpass switching diodes were damaged, my guess is that L4 and Q2 went, L4 going open circuit effectively acting as a fuse / protection component :)So a little time (about 2 hours fault finding) 3 faults and total component cost of £2.45 - I have a working really nice TS-570DGE  working really well - RESULT :)Now to keep or sell - I wonder ?