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Crumbtrail TV Forums: TV Equipment: TV Repair Forum:
Mitsubishi CS27201 repair

 

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Auburn Boy
New User

Mar 9, 2018, 10:29 PM

Post #1 of 37 (1189 views)
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Mitsubishi CS27201 repair Can't Post

Greetings! My first post here.

I'm looking for help diagnosing and repairing my 27 inch Mitsubishi.

I have obtained the manual and started troubleshooting it.

The SYMPTOMS that started were: very dark screen starting up. After about ten minutes or so, the screen brightened and seemed normal. Everything else was good.

As time went on, the main symptom worsened until the screen NEVER brightened. Audio still worked, and video would pass through from S-video in through to the RCA video and audio outputs.

The manual goes by the document title:
mitsubishi_cs-26301_chassis_xm0_sm.pdf
(Slightly different than the model number, but it is apparently the same chassis!)

I have dug into the electrical debug a bit, and if anyone wants to start a dialog with a HOBBYIST, I would really appreciate it.

I can go further into what I have already found and tried..,

Thanks in advance!



jts1957
Veteran


Mar 9, 2018, 11:25 PM

Post #2 of 37 (1181 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

Which model / manual do you want to reference? BOTH mentioned in your post Have a Sams Photofact available. Actually BOTH are the same.

XM-0
CK-27304
CK-27306
CS-26201
CS-26301
CS-27200
CS-27200A
CS-27201
CS-27301
CS-27303


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Location: Far, Far Away

(This post was edited by jts1957 on Mar 9, 2018, 11:43 PM)


Auburn Boy
New User

Mar 10, 2018, 12:24 AM

Post #3 of 37 (1171 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

I assumed the two units used the same manual.

I am working on a CS-27201.


jts1957
Veteran


Mar 10, 2018, 12:41 AM

Post #4 of 37 (1167 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

So as for your initial post, have you tested the CRT?
And what is rest of the story? ("what I have already found and tried..")


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Location: Far, Far Away


Auburn Boy
New User

Mar 10, 2018, 1:04 AM

Post #5 of 37 (1164 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

Ah.., The rest of the story.

I was testing the various supply voltages and had found all seemed good but the tube kept turning off (Horizontal voltage drive OFF.) I had tested the +5, +12 on the standby side as OK, and the hot side voltages checked out as well, the

Then, being a bit of a novice with CRTs, I accidentally shorted out the primary 130 volt to the "common tie point" return. Replaced the DC side 2A fuse and started over with the supply voltages, the regulated 12 and 9 supplies, would turn on but shut down again.

The H (B+??) voltage was measuring 163 V instead of 130, so I started questioning the STE3230 Vreg, and found that the return load resistor, a 2.2ohm 15 watt wirewound had opened as well as the fuse.

I got that fixed with a replacement from MOUSER After this, the H B+ supply read 130.5 volts (nominal) but would not turn on the hot side supplies again.

Hunting through the schematic, I found the X-Ray Prot shutdown. I found a tip in the Misc Adj. section regarding testing with R521 out of the circuit, disabling the X-Prot input.

This worked as indicated and allowed the CRT side to power up. The CRT lights up, and Audio powers up, but the supplies turn off again after exactly 10 seconds.

The CRT lights VERY BRIGHTLY, indicating that the X-Prot circuit was actually doing its job.

So, here I am stuck for the moment.

What ELSE turns off the secondary supplies? (Needs to be unplugged to be able to repeat..,) The manual also mentions using a variAC to test at this point.

What to test next?

Thanks.


jts1957
Veteran


Mar 10, 2018, 1:39 AM

Post #6 of 37 (1160 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

MARK the screen control (so it can be easily returned to initial setting) and rotate CCW and see if it limits enough to allow set to stay on.
Reducing AC with a Variac might also be helpful.

HOT ground is the Open triangle (Bridge & IC951 (Primary PS) and Horizontal Output mostly) - Cold ground is Filled in triangle - rest of set.
Standby supplies are T991 secondaries - Present as long as TV plugged into Mains.
Flyback transformer has scan derived secondaries - Only present when flyback is driven.


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Location: Far, Far Away


Auburn Boy
New User

Mar 10, 2018, 2:37 AM

Post #7 of 37 (1154 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

Thanks. I will give that a try. The SCREEN INTENSITY seems extremely high.

I forgot to mention, I took the flyback transformer out to check all the coil continuity and found them all good. I got everything back in where it belonged. I wonder if that changed the SCREEN setting??

I figured out that all the secondary supplies were dead when the H B+ voltage was shut off.., They are powered when the scan is operating, as you mentioned.

I'll let you know if I find anything else out. The weekend is upon us. Honey do time..,


Auburn Boy
New User

Mar 13, 2018, 12:11 AM

Post #8 of 37 (1136 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

Wow!

Well, I adjusted the SCREEN setting down about 16th turn and now the set powers up and stays on.

So now I can see extra symptoms.

Screen is very bright white. Menu text (channel to start with) has green slightly shifted from black. All on the very bright white (and tinted) background.

The MENU does not display on the screen when activated, but I was able to "walk through" the menus to get my active house channel (014) up into tuned channels.

Now I get audio and video but the video is basically just a over-driven white with some mixed tint while displaying the active channel.

Sheesh..,

Where to go from here? I'm thinking about putting back the X-ray Prot resistor and see how that does.

How deep the rabbit hole goes..,

With the X-Ray/prot in, it shuts down still.

You didn't mention what other protection circuit might shut it down as I mentioned before with the X-Ray/prot out. I see another line from the F/B Transformer called "APK PROT" is it on the SCREEN/FOCUS ground side and if it is too high, it might cause the processor to kill the A/C through the standby relay???? Just a wild pondering.

I'm thinking there is something driving a bunch of voltages over limit..,

Perhaps a variAC might help with diagnosis..,


(This post was edited by Auburn Boy on Mar 13, 2018, 1:36 AM)


jts1957
Veteran


Mar 13, 2018, 2:19 AM

Post #9 of 37 (1129 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

Voltage across C563 &/or C662?


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Location: Far, Far Away


Auburn Boy
New User

Mar 13, 2018, 5:37 AM

Post #10 of 37 (1124 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

Okay. RGB Driver voltage.

Source: C563 &/or C662 should be 230 V.

I'll measure that (taking out the X-ray Prot feedback again. :) )

If that voltage is TOO HIGH, it would overdrive?

Thanks,


jts1957
Veteran


Mar 13, 2018, 6:55 AM

Post #11 of 37 (1122 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

If either cap was bad (including physical damage), it would affect the voltage too.


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Location: Far, Far Away


Auburn Boy
New User

Mar 13, 2018, 11:51 PM

Post #12 of 37 (1106 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

Greetings again,

Back on the trail.

I found an ERROR in the Mistubishi Schematic. They show pin #5 of connector KB to be the ground. It is not. It is the Q250 Video Buffer driver output from the main board to the R/G/B Bias of the emitter follower (I think that's the type) on the CRT board.

The ground is really on pin 4. It is common with the tuner case ground, the logic grounds on the main board (and I suspect the signal grounds,) and the signal grounds on the CRT board. So, I found a good ground, I think.

Should I be able to use this ground as a ground for my scope should I want to measure signals? (I know I shouldn't use the HOT ground on the primary power supply, ARG. Not AGAIN anyway..,)

No, to the meat of today's investigations.

The sch shows 230 Volts should be on the RGB drive circuits. After the power supply at C563 and C662 I measured 216.7 volts. A little low..,

I could unsolder those and check their ESR.


(This post was edited by Auburn Boy on Mar 13, 2018, 11:53 PM)


jts1957
Veteran


Mar 14, 2018, 1:45 AM

Post #13 of 37 (1102 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

WRONG ERROR.
My copy shows, believe it or not, on the PS page, pin #8 being ground. Considering the plug & socket (KB/DK) each contain 5 pins...
1=Green Drive
2=Red Drive
3=Blue Drive
4= Gnd
5=Emitter of Q250

Personally, I don't use my scope unless TV is plugged into Isolation/Variac.
Assuming house is wired correctly and AC polarized plug hasn't been defeated, you should be O.K.


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Location: Far, Far Away


Auburn Boy
New User

Mar 14, 2018, 5:05 AM

Post #14 of 37 (1081 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

Well,

First I am going to find out the state of the components and voltages around pin pin 5 and pin 6 of the flyback.

Since the DRIVE circuits off of the 230 V supply (which could be somehow overdriven?? Even though they show 216.7 V instead of 230) and the 40 volt X-Ray Protect shutdown hold voltage are both not "right."

(I have yet to figure out what feedback shuts off the power when the SCREEN is too high..,)

Aha!!! APK PROT is pin 6 of the processor. Comes from pin 8 of the Flyback!!!

It looks like another shutdown circuit.

I seem to have a lot of parameters to measure..,

I'll let you know.

Possibly when I shorted the rectifier HOT GROUND, I pulled a few other components into the grave on the secondaries of the flyback..,

Got my work cut out for me.


jts1957
Veteran


Mar 14, 2018, 5:30 AM

Post #15 of 37 (1078 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

Apply a tolerance of between +/- 10 & 20 percent on voltages.


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Location: Far, Far Away


Auburn Boy
New User

Mar 15, 2018, 10:29 PM

Post #16 of 37 (1065 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

Hello again,

I'm making measurements all over the place now.., Interesting.

The X-ray Prot actually makes sense. It is listed in the Sch. as 40.1 volts. I'm pretty sure that is the "on" voltage. I measure 39.5 volts right at power on, and it switches up to 40.2 after 5 seconds. It would switch off the HORIZ if I didn't have it disables.

I haven't yet measured the APK-PROT switching voltages, but I suspect I would see that switch as well if the SCREEN was turned back up.

All the other voltages around the mains PS and the Flyback seem to measure out correctly.

Only when I get to the R, G, and B outputs do I find a problem.

The Sch indicates I should see 191, 195, and 185 respectively at the connector to the CRT. I only measure 70.1, 64.1 and 65.6 volts.

This was using pin 4 of conn DK as the ground reference.

Would LOWER voltages here provide the "HOT" image and thus the X-ray Prot and APK Prot shut downs?

If the LA7674 video signal processor is out, I think the set is toast..,

Thanks,


jts1957
Veteran


Mar 15, 2018, 11:24 PM

Post #17 of 37 (1063 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

https://www.ebay.com/...hn=ps&dispItem=1 Not end of world. Bad CRT might be.

X–Ray Protector Circuit
Operation Input Voltage Pin #24
VHD Min0.64 Typ0.74 Max0.84 V

Voltages on Q250? Also IC200 voltages on pins 18, 19, 20?


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Location: Far, Far Away


Auburn Boy
New User

Mar 16, 2018, 12:10 AM

Post #18 of 37 (1061 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post


In Reply To
https://www.ebay.com/...hn=ps&dispItem=1 Not end of world. Bad CRT might be.

X–Ray Protector Circuit
Operation Input Voltage Pin #24
VHD Min0.64 Typ0.74 Max0.84 V

Voltages on Q250? Also IC200 voltages on pins 18, 19, 20?


I measure the X-Ray prot on D582 from 39.5 to 40.2.., dV 0.7 So that's the switching voltage, and it does indeed switch..,

I can more easily measure the voltages delivered to the CRT board. The bases of Q651, Q652, and Q653. Also, the collector of Q250 on conn DK pin 5.

Again, I'll try to measure APK PROT as well.

Thanks,


jts1957
Veteran


Mar 16, 2018, 12:53 AM

Post #19 of 37 (1058 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

X-Ray protect monitors the 40.1V supply. The six components between that source and pin #24 of IC200 form a voltage divider and filter. The voltage at pin #24 is what triggers Horizontal drive/HV shutdown. Minimum0.64 Typical0.74 Maximum0.84 Volts
See page #2 High voltage shutdown & Test.


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Location: Far, Far Away

(This post was edited by jts1957 on Mar 16, 2018, 12:56 AM)


Auburn Boy
New User

Mar 16, 2018, 6:05 AM

Post #20 of 37 (1043 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post


In Reply To
X-Ray protect monitors the 40.1V supply. The six components between that source and pin #24 of IC200 form a voltage divider and filter. The voltage at pin #24 is what triggers Horizontal drive/HV shutdown. Minimum0.64 Typical0.74 Maximum0.84 Volts
See page #2 High voltage shutdown & Test.


Yes, I found all that..,

Would 40.25 shut down the H voltage?


jts1957
Veteran


Mar 16, 2018, 6:10 AM

Post #21 of 37 (1040 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

Doubtful.


Quote
Voltages on Q250? Also IC200 voltages on pins 18, 19, 20? And Now 24?


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Location: Far, Far Away


Auburn Boy
New User

Mar 16, 2018, 9:32 PM

Post #22 of 37 (1031 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

Pin 24 is disconnected to keep the set on..,

The voltage there was as I mentioned earlier.

At power on it starts at 39.5. After 5 seconds it switches to 40.25.

I can't get to the IC200 pins very easily, neither the Q250. But!!

The RGB Drive outputs are HALF of what they should be.

The output of Q250 (on BK pin 5) is ONLY 1.99V

I have yet to measure the APK PROT pin..,

Would the cold ground be a good ground for a scope probe???


jts1957
Veteran


Mar 16, 2018, 9:46 PM

Post #23 of 37 (1028 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post

Reconnect Pin #24 an lift either end of R521 and post voltage(s) at pin 24.

You can measure at any point on a foil trace that connects directly to the TP in question.

For cold ground measurements Yes.


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Location: Far, Far Away


Auburn Boy
New User

Mar 16, 2018, 10:45 PM

Post #24 of 37 (1023 views)
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Re: [jts1957] Mitsubishi CS27201 repair [In reply to] Can't Post

Hi,

This is getting interesting. I managed to pull the MB out far enough to probe just about everything. (Keeping it precariously balanced but not shorted.., BOOM!)

I've always had R521 lifted to keep the set powered up..,

Pin 24 of IC200 measures 4.89 v.
Pin 21 is 0.785 v.
Pin 20 is 4.83
Pin 19 is 4.83
Pin 18 is 4.83

Q250 measures: B = 2.21v,, E = 2.1v, C = 0.0v.

The APK PROT pin measures 4.919

Something doesn't seem right in River City.., Q250 is toast?? I notice one of the pins on it looks badly soldered??????? I'm going to re-solder it for now..,


Thanks,


(This post was edited by Auburn Boy on Mar 16, 2018, 10:47 PM)


jts1957
Veteran


Mar 16, 2018, 11:17 PM

Post #25 of 37 (1018 views)
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Re: [Auburn Boy] Mitsubishi CS27201 repair [In reply to] Can't Post


Quote
Pin 24 is disconnected to keep the set on..,

The voltage there was as I mentioned earlier.

At power on it starts at 39.5. After 5 seconds it switches to 40.25.


AND


Quote
I've always had R521 lifted to keep the set powered up..,

Pin 24 of IC200 measures 4.89 v.


Major discrepancy #1.

-------------------------------------------


Quote
Pin 21 is 0.785 v.
Pin 20 is 4.83
Pin 19 is 4.83
Pin 18 is 4.83

Q250 measures: B = 2.21v,, E = 2.1v, C = 0.0v.


Discrepancy #2. 100 ohms apart, I think should be closer.

Q250 should be easy to remove and test.


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Location: Far, Far Away

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