Amps
[Top] [All Lists]

Re: [Amps] RM Italy BLA350

To: amps@contesting.com
Subject: Re: [Amps] RM Italy BLA350
From: Steve Thompson <g8gsq72@gmail.com>
Date: Wed, 24 Jun 2020 10:59:29 +0100
List-post: <mailto:amps@contesting.com>
Sadly you're right on both counts there. I can see there's some overdrive protection on the input which switches in 10ohms across the input to the transistors if the drive goes too high - but it doesn't latch and when the input sampler evaporated the trigger signal was probably lost so it would have dropped out.

Hopefully the TL084 has survived and it didn't get into the low voltage supply rails.

Quick tests for FETs using a DVM:
D-G and G-S should be very high resistance any way round. I'd be suspicious of <10M Connect G-S and look at D-S in diode check setting. -ve to D should show a diode drop, +ve to D open cct and should stay that way for at least a few seconds if you remove the G-S connection and let G float.

Apply +5V to the gate. D-S should show close to short cct, and stay that way for at least a few seconds after removing the gate volts and let G float.

Good luck
Steve G8GSQ

Thank you Steve,

I have lifted the gate and drain of both devices to measure them. One device 
shows a short from drain to source so I suspect they are indeed blown. Other 
one measures 300k S-D but open D-S. But with one showing a short I think both 
have to go regardless.


For the 3dB pad, In to Out 2.5k, In to Gnd 2.5k, Out to Gnd 92 Ohms. I think 
that's not so good either.


Martin, HS0ZED
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps

<Prev in Thread] Current Thread [Next in Thread>