Re: Tek475 strangely in heat


adenton <adenton@...>
 

Hot means too much current at too much voltage -- power = volts x
amps and all that. If the voltages are OK look for excessive
current. High heat is NOT normal. A common cause of excess current
is a leaky capacitor, either supplying excessive base current, or for
example in bypassing an emitter resistor thus greatly increasing
emitter/collector current.

Depending on the circuit configuration, it is possible for this to
happen without apparent malfunction, especially in a differential-
amplifier circuit. Since yours are duals, I strongly suspect that.
Check all those caps for leakage. Strap a current meter in one of
the emitter circuits and measure the juice. This times the CE
voltage gives you the power dissipation which you can compare against
the case type. (Although you already know it's too high.)

Note, caps sometimes check OK at low voltages (VOM ohmmeter) but leak
like fishnet at circuit voltages. Perhaps a current-meter in series
with the cap, with the circuit quiescent. (If it's in the sweep, try
single-sweep mode etc.)

Which suggests a topic, Does anyone know anything about electrolytic
capacitor leakage??? (JUST KIDDING!!!)

--- In TekScopes@yahoogroups.com, "josko_flander"

A pair of double transistors (Q914 and Q938) is literarily
steaming. They are too hot to touch.

Join TekScopes@groups.io to automatically receive all group messages.