Q7 in Heath HD-1410 keyer
 

I was noodling around with my HD-1410 keyer while tuning up my Eico
720. Then the AC power had a brownout, and a bright orange flash and
loud pop came out of the keyer. Opening it up reveals that Q7 is now a
bunch of little pieces of burnt plastic. The keyer beeps the internal
sidetone but now no longer keys the transmitter.

About a quarter century ago when I built the keyer, I remember
something similar happening (except I think it failed shorted), and I
seem to recall that Q7 is just a NPN maybe HV transistor, probably
something like a MSA42. Can someone confirm this?

Tim.

Q7 in Heath HD-1410 keyer
 

In article .com,
wrote:

I was noodling around with my HD-1410 keyer while tuning up my Eico
720. Then the AC power had a brownout, and a bright orange flash and
loud pop came out of the keyer. Opening it up reveals that Q7 is now a
bunch of little pieces of burnt plastic. The keyer beeps the internal
sidetone but now no longer keys the transmitter.

About a quarter century ago when I built the keyer, I remember
something similar happening (except I think it failed shorted), and I
seem to recall that Q7 is just a NPN maybe HV transistor, probably
something like a MSA42. Can someone confirm this?

Tim-

According to a diagram I found of the HD-1410, Q7 is a Heath 417-294.
This crosses to an MPSA42 Motorola transistor, per the cross reference at
http://www.d8apro.com/heath3.htm with specs shown as NPN, 300V, 500mA,
TO-92, 50 MHz.

Be sure to check Q6 (also a 417-294) and D5 (57-27, 1N2071).

73,
Fred
K4DII