Sharp TU-95PA Black & White 12"
 

Hi guys,
This is my first post here. I am a longstanding member over at audiokarma and have had great luck there with my audio projects. Hoping someone here can help me with my little B&W set. It has been working all these years until about two weeks ago when I remove the back to blow out the dust. Afterward, I turned it on with the back still off to make adjustments to a couple things that are covered when the cover is on. I accidentally touched two terminals (I think) on the power switch with my watchband. There was a small spark and the set went dead. No picture, no sound. I'm puzzled because it looks like all of the tubes are still on. I can't seem to find any fuses so I don't know what to check. Any help would be appreciated. I purchased the SAMS manual, but I don't know where to start. Thanks in advance!

And that is why I don't wear a watch or jewelery...

The set is probably a series wired heater set. It may also have instant on (which went under a plethora of trade names).... B+ and heater are often separate circuits.

Sam's will have voltage listings that you can compare against. Some sets of the era had fusistors (resistors designed to open under fault current), and fusible links (segments of thin wire intended to act as fuses).

If you can't find any fuse action devices you are going to have to troubleshoot....TVs are difficult to fix affordably through the change random parts till it works approach. Gotta learn how to ID what failed and correct it. Post the schematic and we can help walk you through troubleshooting.

Edit: BTW if this has tubes other than the CRT it should probably be in the rectangular screen tube TVs section or the early B&W section and not in solid state TVs section like it is. click the red and white triangle at the top corner of your first post to report the mistake to a moderator and they will help you move it to the correct section where more people will read this.

Thanks, Tom. The set is definitely an instant on type. I did find a fusible link but it tested fine.

Here is the schematic. I had to scan it two halves. I did notice in the troubleshooting section it says to check R710, which I haven't done yet. Could the fix be that simple?

Yes R710 is a very likely culprit(confirm with resistance check). If it isn't the culprit check the 152VDC source down stream of it for voltage.

If 710 is open you can jumper it with a 1A fuse to confirm nothing else is wrong...if the 1A fuse pops something is shorted down stream such as the diode, filter caps or a B+ line(s). If all is right and you don't happen to have a correct fusistor laying around, replace it with a 1A fuse in series with a 4.7 ohm resistor of correct wattage.

I took the set to my friend's house for him to look it over. After checking the diode, and other items, he noticed a wire on the back of the on/off switch was broken. As soon as we fixed that the set worked again!
The original fusistor is broken, one of the leads broke off right where it goes into the body. Right now I have just a one amp fast blow fuse taking its place. You had mentioned placing a 4.7 ohm resistor in series with the fuse. How do I determine the correct wattage? I tried a 1 watt resistor and it blew right away. Can I just use the set with only the fuse?

Thanks again for all of your help. I posted a picture of the broken wire my friend found.

4.7 ohm 5 watt was in 95% of B&W tube sets. Must be a fuseable.

73 Zeno:smoke:
LFOD !

Thank you, Zeno!

It turns out I need to replace the on/off volume switch. What I found online should work, except that on the power connections, the original switch has four terminals and the new ones I've seen only have two. The ones I saw are SPST switches. Does that mean I need a DPST switch? I think the extra two terminals on the original switch allow the tv to have its instant on feature.
The terminals are labeled as follows, starting with the green lead, counterclockwise:
Green Lead=D
Red Lead=F
Black Lead=C
Jumpered Lead from Green terminal=A

It is the 115 ohm in parallel with the switch that enables the instant on. I personally don't like instant on as it can wear out the tubes... what I would do is snip out that 115 ohm resistor and bridge the fusistor terminal over to the heater terminal of the switch.... another option that would prevent changing the control and also prevent switch wear is to have the good section of the switch drive a the coil of a 120VAC coil DPST (or a correctly wired DPDT) relay.

The problem is the volume pot is broken, one of the two fingers broke off. The other problem is that the shaft does not activate the on/off cam either. I attached a pic of the on/off cam, I added a small bit of epoxy to the off side so the post would make sufficient contact, but then I noticed that one of the fingers for the volume had broken off. I'm guessing that installing a new dpst switch may be the simplest fix since both sections are broken. Do you agree?

If the pot is bad and the switch mech isn't being actuated by the shaft it's definitely time to replace the whole control.

I thought only one switch contact was dead thus the suggestions to keep it going on what I thought was still usable...

I ordered one of these. Will this work? If it is, I may have a question about wiring when I receive it.
Thanks for all of your help so far, Tom.

https://www.mouser.com/ProductDetail...rrencycode=USD

I got a new switch from mouser, installed it today and the set is working perfectly. Thanks to all who helped me along the way. Good day, guys!

Amazing teamwork and trouble shooting!!