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#1
11-17-2010, 09:53 PM
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Motorola 9T1, did I ruin it?
I picked up a Motorola 9T1 a few months back, in pretty complete and reasonable looking condition, so last night I decided to see if I could get it to do anything. I start by checking out the chassis. There are quite a few wax caps under there, but nothing showing signs of failing. I hook up a modulator and DVD player, hook the set to a variac, and hook a DVM to the B+. Initally I just get scrolling garbage on the screen, then after a long time tweeking the knobs on the back of the set, I actually get a real picture. I can adjust the size, position, etc and it actually looks pretty good, and the sound is working too. I watch it this way for several minutes, then shut it down. I still have the variac at less than 90%. Tonight I try it again, sound seems fine but nothing at all on the CRT. B+ is about the same as yesterday. This is the first TV project I've decided to tackle so my plan was to keep things working while replacing a couple wax caps at a time. Now I'm worried I've run it too long with the old caps done something that can't be un-done, and don't have the experience to know how to proceed. Could I have damaged the picture tube or flyback? Is there a part of the circuit that I should check out first? Maybe I lost high voltage? I hate to probe around that area too much without knowing exactly what I'm doing
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#2
11-17-2010, 10:24 PM
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Damage? Doubtful. Completely boogered old caps? Very likely. 9 times out fo 10, the horizontal section is gonna go down first because it's under the most stress. That means you loose HV, so it explains lack of a picture. Recap the whole thing before you go any farther, I learned the hard way that recapping piecemeal is bad juju.
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Evolution... 
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#3
11-17-2010, 10:49 PM
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Besides the capacitors the selenium rectifiers need to be replaced if they haven't been already. If the seleniums short or the electrolytics short they'll take out the ballast tube. Those were impossible to find for a time. I'd buy a spare now.
You can also make up a resistor replacement for the ballast and it might be wise to use one until you get the set fully restored and working. John
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#4
11-17-2010, 10:57 PM
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Sounds like a good starting point to me. The only reason I was wanting to do piecemeal is that if I broke something in the process, I would at least know where to look. Well, now that it's already broke, that's not going to help me much. That said, I will probably focus on things HV related at least for starters, but the whole set will get recapped very soon. Phil, I've run into many wax caps that look good but are dead, no surprise there. I fully expected to apply power and get 60 cycle hum from the speaker, I was kinda shocked when it actually worked. There is no power transformer in this set to burn up, so I mainly wanted to make sure that I didn't do anything to harm the picture tube or flyback before I went any further, as I can't easily replace them. Thanks for the help, hopefully this set will be an easy fix so I can move on to a couple more involved projects!
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#5
11-17-2010, 11:06 PM
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John, I replied before I saw your message. I have had pretty good luck with origional selenium rectifiers in old radios, as long as they aren't getting warm/hot. I haven't run the set with the chassis out of the cabinet, so I'm not sure how these are doing... but I was origionally going to keep them in place as long as they were working okay. I never thought of them hurting the ballast... so I might rethink that. Would a resistor replacement cause any cold filament surge that might hurt the CRT heater? Shouldn't be a problem while I'm testing as I'll be bringing it up slow on the variac, so I'll look into a resistor sub for that. Banderson: No flyback? Shows what I know, but I'm glad to hear that there's one less thing to burn up!
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| Audiokarma |
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#6
11-18-2010, 04:03 PM
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Quote:
I finally decided it wasn't worth the bother of trying to keep them. John
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#7
11-19-2010, 05:02 PM
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I've only replaced one selenium so far, in a Zenith AM/FM radio; it was working but was getting warm and B+ was dropping off a little after it warmed up. I got the caps I need ordered from allied today, thanks everyone for all the help so far!
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#8
11-17-2010, 10:44 PM
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Quote:
Phil Nelson
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#9
11-17-2010, 10:58 PM
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Also these sets don't have a flyback, yoke or horiztonal output tube to burn up
Instead there's an RF oscillator and HV coil under that aluminum can. They're probably alright.
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#10
11-17-2010, 11:14 PM
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Yes, there will be more surge current with resistors. Try to use "A" type tubes like a 6AU6A. Those are designed for series filament sets and they warm up more evenly.
Also adding a thermistor like a LC-90 is a good idea too. It's a device that looses resistance as it heats up and will control the startup current surge.
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| Audiokarma |
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#12
11-18-2010, 03:10 PM
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Allied Electronics has them
http://www.alliedelec.com/catalog/pf...f&pageNum=1677 And also JustRadios http://justradios.com/ I get the 8000 or 10000 volt ones when possible, they are cheaper than the 6KV caps and will still be far smaller than the originals.
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#13
12-16-2010, 09:06 PM
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Sweet
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