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Winston Winston is offline
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Default Grundig AM/FM portable "Transistor 305" troubleshooting

klem kedidelhopper wrote:

(...)

There is a note near the battery connector which indicates what
appears to be a quiescent current between .020 and .022A. In fact when
I started this project I measured .025A on the bench power supply with
7.50V applied to the battery terminals. Therefore, given my initial
quiescent current reading, if all that current is indeed flowing
through R46 then I should have dropped 2.50V across R46. However I
never monitored that point so I didn't know. This morning the radio
was still working and I noted that Vr46 was .840V. Quiescent current
is still .025A. So now I'm really confused. Are you supposed to start
off with 9.0 Volts at the battery terminals for voltage measurement
purposes or is it 7.50 Volts? I can say with every certainty that with
7.50V applied the actual circuit voltages did almost mimic what the
schematic shows when the radio was operational. Or has my supply been
at least 1.50V - 2.50V too low throughout this experiment? Lenny



'Sounds like your 'rail voltage' ended up at 6.66 V considering
the 0.84 V drop in R46 or about 90 mV below the minimum indicated
on the schematic.

Were it me, I'd adjust the power supply until the rail voltage
measured, say 6.88 V.

It's an exercise anyway because you apparently found
and fixed the bug.

That's the important thing.

--Winston