[Icom] R75 went deaf after lightning

[Roy Sakabu]

Often times it is the first semiconductor unit in the RF chain.  I've fixed
a couple of other manufacturers receivers this way.  In the R-75 Yahoo
groups files section, there are complete schematics and block diagrams.  You
can follow the RF path in the block diagram as well as the Schematics,
especially Main Unit (1).  That's probably where your blown front end is.

You said deaf on all bands.  Is it also deaf with the Preamp on/off,
Attenuator on/off also?

 I would first check R102 and R112 to make sure they didn't fail to short
circuit (assuming that your R-75 is deaf on BOTH A and B antenna inputs).  I
would then check to make sure D141 and 142 (the "protection" diodes) didn't
short to ground.  Then check Q471, then Q441 and Q442.  By then you should
probably have found the culprit.  Q441 and 442 are part of the mixer circuit
and Q471 is part of the IF amp/AGC circuit.

Good luck
Roy
AD6ZU

> ----------
> From: 	Ekki Plicht[SMTP:ekki@plicht.de]
> Reply To: 	icom@mailman.qth.net
> Sent: 	Monday, October 14, 2002 7:37 AM
> To: 	_icom
> Subject: 	[Icom] R75 went deaf after lightning
> 
> Hi,
> while running my R75 receiver on an indoor dipole, a thunderstorm came
> along. 
> While there was no direct hit to my house or in the close vicinity, the Rx
> is 
> deaf nevertheless. My guess is that the closest lightning struck about 500
> 
> mtrs away from me.
> 
> Does anybody know where to start looking or how to indentify the faulty 
> component? The rx is deaf on all bands.
> 
> TIA,
> Ekki, DF4OR
> 
> ----
> Your Moderator: Dick Flanagan W6OLD, icom-owner@mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.315 MHz
> Icom FAQ: http://www.qsl.net/icom/
> 


--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment. Attachments are not allowed.
Please post in Plain-Text only.---