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#1
05-26-2013, 01:54 PM
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84' Mitsubishi CS1984R - Startup Issue?
I have a 1984 Mitsubishi CS1984R 20" Stereo TV. It powers on, the channel change display comes up, but It seems I'm not getting any power to the Cathode Ray Tube, and there's no lights on the audio panel. I'm kind of against junking it as this set was working great beforehand.
A possible cause might have been accidentally bumping into the power button a few times rapidly while cleaning, I read this wears on parts of the circuit. Looking around inside, the service labels were floating around loose, I managed to retrieve one with a plastic ruler and dump the other out. Thankfully one of them gave me the location to all the fuses inside the TV. I can';t get THAT good of a look but it appears they all are unbroken (probably need to discharge the Anode Cap and dig deeper to be sure). Also on my visual inspection, I see there's a weird spring/fuse-internals looking thing screwed onto a metal heatsink for the HOT just under a large ceramic case resistor. The "spring" is bent and pointing down toward a seemingly corroded hole on the Flyback transformer. Reading this guide - http://www.repairfaq.org/sam/tvfaq.htm#tvnopicorns - Going off of this, it seems I may just have a problem in the startup circuits as I am not getting a high pitched whine at all (that Classic Mistubishi whine I've known since I was a kid) nor static-E on the screen, plus the neck of the tube shows no signs of light (which it usually does). I'm kind of new at working on the old CRT TV side of things, but I feel with the retro things me and the family are into it might be a good idea to learn. Would love to get this thing fixed, the picture on it was amazing enough to use my old Tandy 1000 PC iwth it, even for text mode. 
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#2
05-26-2013, 02:29 PM
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I don't have any advice, but just wanted to comment on the set itself. I used to have the 15" version. Great set. Does yours have AV inputs? Mine did not.
Hope you get it fixed. Hard to beleive that set is now 30 years old.
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#3
05-26-2013, 06:19 PM
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You have one of the old MGA's thats good. They were much better
than the newer ones, MGA actually stooped to rebadging some Sharps on some models. That really pissed off a few customers when they found out !! ( he he he I told them) Anyhows the flyback pix is a bit out of focus but looks normal. The CRT filaments WONT light without HV. IIRC there is no "start up" circuit in this set, thats good. I dont think it has anything to do with the buttons, its just the long arm of coinsidence at work ! I assume you have a meter. Double check the fuses with it. A common fault is cold solder on the hoz drive transformer & in the area of the hoz out transistor & flyback. Also at the on/off relay. The small black xformer behind the flyback in pix is the hoz drive xfrmr. IIRC these sets also got cracked PCB's along the back edge............ Dont know your abilities or equipment but this is an easy set to deal with so if you have the basics we can walk you through...... Let us know. 73 Zeno
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#4
05-27-2013, 12:17 PM
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Update...
I just discharged the anode (no current in it anyway), and pulled the chassis (he's right, this thing is pretty easy). Now for what I have found. Sounds like no charge in the Anode cap when I discharged it. Either this thing must be pretty good at discharging itself when turned off, or maybe the lack of high voltage on startup has drained it. Thankfully no cracks in the board. A lot of the solder joints, especially on the flyback side, are not very shiny. Went through and discharged all caps and potential voltage stored to chassis ground to make sure the set was safe for testing. Using a digital multimeter to test all the fuses, all of them are in 100% working order. Upon closer inspection, there is a metal rod running up the side to the top of the Flyback, and when I touched on the little round bit, a piece of aforementioned "spring" came off, all corroded and rusty exposing a rusty rod that it must have been soldered to. What would this be doing...it almost seems like it's some kind of ground or fuse that fried or corroded away. Still not sure weather to concern mys elf with that or not. Another suspicious thing I found was a black relay on the flyback side towards the front labeled RP901 that was loose on it's pads I decided to re-solder it...it's nice and tight now with a shiny new connection. Looking at the pads for the tiny transformer (HOZ) in the Flyback section, they don't look all that shiny so I will resolder those as well.
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#5
05-27-2013, 02:00 PM
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Another Update - got the set back together, no change.
Took a second look at that black component (PTH451A) - that's actually a Thermistor after looking up the number. Tested the HOZ Output Transistor(s). the 2SD869 next to the Flyback was 542 ohm on both prongs. The STR384A tested 594 on one side, and 194 on the other....not sure if that's right or not. Is it normal to have a Set as clearly laid out/labeled as this (ie, large white outline labeled with "power", "dega (Flyback)" Video 1 (Base video), Video 2 (Tuner),, and every single cable inside the case is labeled and keyed to fit properly only one way. Zeno was not kidding when he said this was an easy set to work with. Takes me about 15 min to get the board out including discharging the anode and removing it.
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| Audiokarma |
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#6
05-27-2013, 02:56 PM
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I see what looks like a tantulum cap in the second to last picture. Might want to replace those, as they're even more failure prone than normal electrolytics, or so I hear.
Really though, a great set like this deserves a total recap.
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#7
05-27-2013, 06:24 PM
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Thermistor is for degauss.
Most solid state sets bleed off HV fast so no clue there. Find on/off relay, USUALLY black, rectangle, 4 pins, near the DGS thermistor. Cant see in pix. Check it for bad cons. Quick tests: Check DC at STR. The big resistor above it should have 150v one side apx 130 on other. Check hoz drive xformr primary abt 75V sec abt 0V. Check hoz out, case ( collector) abt 130V Get back with results........... 73 Zeno
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#8
05-28-2013, 03:09 PM
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Quote:
I picked up the Service Manual for it online today. I was quite shocked how much stuff on that set is under-used, I did not even know it had an internal clock on it until now (shows time on the OSD), I've been using/messing with this TV set since I was 6 years old. I know at least one Relay inside the set is functional because when I power it on it has that audible "click" of a relay. Now that I have the service manual, I know which board is which. I pulled the sound PCB yesterday and checked around, might be the CRT PCB (the one above it) that might have something to do with what's wrong if it's inline with the main power source like the audio is. I will let you all know when I get the results, as I tend to be a tad paranoid about working around HV when the set is on, I will be running temporary wires out of the case while testing. One thing I have noted is it seems the HV circuits are not even getting powered up, I've not heard one snap of current when discharging the anode cap, and I've been having some pretty close relationships with those HV area components (HOT, Flyback, Anode) looking for faults and all.
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#9
06-09-2013, 02:55 AM
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It seems the high voltage Circuit for the CRT is not getting enough voltage for some reason from early on in the chain. The fuses are all good, and the one confirmed Relay is switching (it's on the Sound PCB, which is also what the power cord goes into before anything is sent to a transformer).
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#10
06-09-2013, 08:29 AM
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Suppose you got dead caps somewhewre in there? this thing is nearly 30 by now.
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| Audiokarma |
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#11
06-09-2013, 12:38 PM
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OK this should be a gravy job. Sams dont make a manual so I
pulled a similar chassis CS1952. This part of the set should be the same BUT I cant be 100%. Use the tuner shield for ground. Relay K702 will have 125 VAC on 2 terminals (when on) if only on one relay is bad. Watch for bad PC cons !!! Check R901 2.7 ohm 10 w. If open test D901,2,3,4 probably one is shorted ALWAYS replace all 4 in a bridge if one is bad. If OK so far check for 160VDC on 1 amp fuse F902. If OK check DC volts at STR381 regulator & report back. 73 Zeno 
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