View Full Version : Zenith space command 300 trouble


LADR
10-05-2017, 05:07 AM
The remote chassis is completely dead, ive replaced the questionable caps and still dead, i was thinking one or more of the transistors are bad. What do you think?

Electronic M
10-05-2017, 09:32 AM
Got a schematic? If so check the PS and other voltages against it. Also may be worth scoping it. The mic could be bad, the mic could be good along with the signal chain and the tuning slugs for each function could be off.

LADR
10-05-2017, 12:04 PM
Got a schematic? If so check the PS and other voltages against it. Also may be worth scoping it. The mic could be bad, the mic could be good along with the signal chain and the tuning slugs for each function could be off.

Yes i have a schematic and were in blazes would i get a mic if mine is bad. Im thinking about just replacing all transistors one by one until i find a possible bad one and I'll check the resistor while im at it.

Electronic M
10-05-2017, 12:14 PM
Better to find the problem than fix it by shot gunning. In the ~3-4 space command sets I've worked on none had bad transistors, and none had bad microphones.

Signal tracing and or injection are the fastest troubleshooting methods for the remote chassis. These things need to be aligned, and component replacement can change the alignment....Blind parts swapping will usually NOT make it just work. I often will scope the signal to make sure it gets down the chain (and fix any stage that is preventing that), inject a signal generator and tune it through the ultrasonic range to make sure the relays respond to SOME frequency (and fix if they don't) then switch back to the mike and then tune the relay channels to the remote buttons.

zeno
10-05-2017, 05:23 PM
IIRC I never had a SC failure on the older sets except the rocker
switches on the tuner & thats not your problem.
If you havnt check the remote-manual switch usually on
the SC chassis. You could clean it too. If you did need an IR
mic any old Zenith one should work.
Another test is rattle a bunch of keys in front of mic. That will
give a response even if out of alignment. The hand unit should
give a good snap & feel solid just like a gun with a sweet trigger.
There is a thin spring in there that holds the tuning rods that
often broke. That all should narrow things down......

73 Zeno:smoke:
LFOD !

LADR
10-07-2017, 06:59 PM
Ok, ive tried keys, coins, screws even a tone generator and absolutely NOTHING happened, so i think its either the amplifier transistors or/and the microphone.