magnavox t80908 problem
 

i got a 1981 magnavox t80980 from the curb with the cord cut i spliced the cord and just the tuner led turned on no picture or sound any suggestions on what this might be

thanks-chris

First thing on Maggies of this time is to pull the chassis back
& look for cold solder joints. Also check the modules them self
where the connectors are. Check for burned pins also.
Do this especially on the R side where the HV & power supply are.
After that you will need a good meter & a litle knollage to go farther.
We can help along....

73 Zeno:smoke:

Yes, check the solder connections on the 703744-1/2/3/4 board - the heat sinked transistor would develop intermittent connections, leading to failure.

Good point abt the board. Also since the LED & micro run on
a separate supply try the circuit breaker if it has one. The
chassis before this did. Near where the cord goes in.

Brian. wernt the 703744 boards on the T991 & the boards on
T809 sets 704###-# or is my mind shot ?

73 Zeno:smoke:

If the circuit breaker is tripped and trips again when you reset it, I'd first check the four-lead safety capacitor (these were very high failure items). You'll probably have a hard time finding one; but, you can replace it with a some high voltage orange drop capacitors wired in parallel to get the correct value. If the cap is not shorted, other possible suspects are the horizontal output transistor, the regulator transistor, and HV tripler (some of these used an IHVT, instead of a separate fly and tripler).

If the circuit breaker is not tripped, you need to make sure that the relay on the control module is closing. If it's not closing, no power will get to the TV chassis. Sometimes, these relays will get stuck in either the open or closed position.

If the relay is good and power is getting to the main chassis, the "dead" condition is likely due to either a power supply regulator issue or a dead horizontal oscillator or horizontal driver stage.

Regardless of what's wrong with this set, you'll still need to take the time to resolder anything that plugs in on the sweep/power supply side of the chassis. Heck, you might need to resolder every module plug and it's associated chassis connector.

Once you fix those problems, you'll have a decent set that should last a long time.

thanks im a huge fan of your youtube channel

BTW, the safety capacitor is supposed to show a short between each set of end terminals; but, it should not show a short from end-to-end. If you have to go with an orange drop capacitor, simply bridge each set of end terminals together. About 8-10 years ago, one of these came in for repair and I fixed it by using orange drops in parallel to get the right value. It worked and the set didn't come back to bite me; so, I guess it held up. Most of the time, that cap will short and trip the circuit breaker; but, they will sometimes open and cause the HV to skyrocket. When this happens, the neck of the CRT will usually be cut off (Zenith had a big problem with this on the early Chromacolor II sets).

what board number is the bad capacitor on

It's not on a module. It's on the motherboard, close to the horizontal output transistor (right hand side of the chassis).

what number is the mother board

I don't know. It's the big board that everything plugs into.