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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Oct 23, 2012 12:26 am Post subject: Some Fun For You Techy Guys |
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So I got this JVC CRT RPTV with a problem and I wanted to get it fixed because, well for 1 thing I like RP CRT displays. But also because this model upscales all inputs to 1080i, has a built in digital tuner, 81pt convergence and 2 HDMI inputs, along with a pile of other goodies.
So lets see how you do, just for fun. And don't be afraid to throw out any thoughts. This is a learning lesson.
So here's the symptoms. I'm a big believer in finding all the symptoms when doing diagnosis.
First symptom is after being on for a while the sound would go high when trying to adjust and then would not respond to any adjustment, just full volume. Would have to turn off for a while. This was when using internal tuner. First i thought it was just a sound problem. Then when I tried the various inputs, they would work for a few minutes and then go out. No sound or picture. Then sometimes when on a particular input you would have sound and picture, and if you tried selecting a different input, the OSD would change but the actual input would not. The component input didn't seem to work at all. But it would always go to the internal tuner input, just no sound.
I've attached a PDF of the appropriate pages to this issue. Ask questions if you like.
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JVC_AV-48P777_SCH_Pages.pdf |
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Oct 23, 2012 12:41 am Post subject: |
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Pin type.
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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Phoenixed
Joined: 13 Oct 2011
Posts: 514
Location: The mitten
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| Posted: Tue Oct 23, 2012 1:37 am Post subject: |
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Nash is trying to catch Analog in post count apparently.
_________________
Planar PD-8150/Runco LS-5
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gjaky
Joined: 05 Jun 2010
Posts: 2802
Location: Budapest, Hungary
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| Posted: Tue Oct 23, 2012 7:47 am Post subject: |
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I guess the problem is with ATSC Tuner PWB, but your attached pdf is corrupted, and I don't find any schematic of that particular board, just for the rest of the set.
_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Tue Oct 23, 2012 11:25 am Post subject: |
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Did you already fix it and are just quizzing us???
I know what the problem is 
_________________
Chip
A Barco is only a AmPro with training wheels
Card carrying member of the AVS chain gang.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Oct 23, 2012 1:17 pm Post subject: |
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| gjaky wrote: | | I guess the problem is with ATSC Tuner PWB, but your attached pdf is corrupted, and I don't find any schematic of that particular board, just for the rest of the set. |
Why would you think the ATSC? I was thinking that also and there are "NO" schematics for the ATSC. It's suppose to be a replace only. It's a standup board off the main.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Oct 23, 2012 1:20 pm Post subject: |
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| stefuel wrote: | Did you already fix it and are just quizzing us???
I know what the problem is |
Yes, it is already repaired. The cause and solution are interesting. And it's a little boring around here so I thought this would bring some interest instead of politics.
So, what do you think the problem is since you say you know? 
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Oct 23, 2012 1:30 pm Post subject: |
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| Nashou66 wrote: | Maybe one of the voltages is not stable and is fluctuating as heat changes?
Wild guessing here
Nashou |
Your guesses are surely good ones but here's what I'm looking for. You need to find the clue as to where to start looking by looking at the schematics.
Once I took all my symptoms into account and then looking at the schematics it showed me were to start looking for the problem.
I'm passing on my trouble shooting skills here and if you guys like this one I'll pass on some more as time goes on.
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gjaky
Joined: 05 Jun 2010
Posts: 2802
Location: Budapest, Hungary
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| Posted: Tue Oct 23, 2012 2:05 pm Post subject: |
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| macgyver655 wrote: | | gjaky wrote: | | I guess the problem is with ATSC Tuner PWB, but your attached pdf is corrupted, and I don't find any schematic of that particular board, just for the rest of the set. |
Why would you think the ATSC? I was thinking that also and there are "NO" schematics for the ATSC. It's suppose to be a replace only. It's a standup board off the main. |
Regarding the schematics the external inputs are selected with IC251 and it goes to ATSC, then ATSC selects between external signals and tuner, this also applies to sound , while the OSD also goes through ATSC, so a hang up on that board could cause similar issues to what you described. That's why I thought 
_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Oct 23, 2012 2:18 pm Post subject: |
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| gjaky wrote: | | macgyver655 wrote: | | gjaky wrote: | | I guess the problem is with ATSC Tuner PWB, but your attached pdf is corrupted, and I don't find any schematic of that particular board, just for the rest of the set. |
Why would you think the ATSC? I was thinking that also and there are "NO" schematics for the ATSC. It's suppose to be a replace only. It's a standup board off the main. |
Regarding the schematics the external inputs are selected with IC251 and it goes to ATSC, then ATSC selects between external signals and tuner, this also applies to sound , while the OSD also goes through ATSC, so a hang up on that board could cause similar issues to what you described. That's why I thought |
How would the ATSC cause the sound to go full on and stay on with no control? And what about the component inputs? They don't pass through IC251.
Keep plugging. Your on my line of thinking.
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gjaky
Joined: 05 Jun 2010
Posts: 2802
Location: Budapest, Hungary
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| Posted: Tue Oct 23, 2012 2:34 pm Post subject: |
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| macgyver655 wrote: | | gjaky wrote: | | macgyver655 wrote: | | gjaky wrote: | | I guess the problem is with ATSC Tuner PWB, but your attached pdf is corrupted, and I don't find any schematic of that particular board, just for the rest of the set. |
Why would you think the ATSC? I was thinking that also and there are "NO" schematics for the ATSC. It's suppose to be a replace only. It's a standup board off the main. |
Regarding the schematics the external inputs are selected with IC251 and it goes to ATSC, then ATSC selects between external signals and tuner, this also applies to sound , while the OSD also goes through ATSC, so a hang up on that board could cause similar issues to what you described. That's why I thought |
How would the ATSC cause the sound to go full on and stay on with no control? And what about the component inputs? They don't pass through IC251.
Keep plugging. Your on my line of thinking. |
They are controlled with the same I2C signals "SCL2, SDA2" also related to ATSC. Any overload on those lines or simple simple contact problem via bad solder joint or bad connector?
_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Tue Oct 23, 2012 2:40 pm Post subject: |
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It's a trick question.
Answer: It's a digital. Not worth repairing, throw it out.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Oct 23, 2012 2:58 pm Post subject: |
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| gjaky wrote: | | macgyver655 wrote: | | gjaky wrote: | | macgyver655 wrote: | | gjaky wrote: | | I guess the problem is with ATSC Tuner PWB, but your attached pdf is corrupted, and I don't find any schematic of that particular board, just for the rest of the set. |
Why would you think the ATSC? I was thinking that also and there are "NO" schematics for the ATSC. It's suppose to be a replace only. It's a standup board off the main. |
Regarding the schematics the external inputs are selected with IC251 and it goes to ATSC, then ATSC selects between external signals and tuner, this also applies to sound , while the OSD also goes through ATSC, so a hang up on that board could cause similar issues to what you described. That's why I thought |
How would the ATSC cause the sound to go full on and stay on with no control? And what about the component inputs? They don't pass through IC251.
Keep plugging. Your on my line of thinking. |
They are controlled with the same I2C signals "SCL2, SDA2" also related to ATSC. Any overload on those lines or simple simple contact problem via bad solder joint or bad connector? |
Ah ha, the I2C bus. That was my conclusion to this point also. For those following along the I2C bus also controls IC621 for audio processing. So do we actually have tuner audio coming out of the ATSC when I dont have sound? So I connected the audio out jacks to a receiver and the answer is yes, I have preamp sound from the ATSC but only on tuner mode.
The bus line also controls IC251 and IC801 which are for input switching.
So what would be next to see if the problem is on the I2C bus line or whats going on with it?
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barclay66
Joined: 27 Jun 2011
Posts: 1304
Location: Germany
TV/Projector: Marquee 9500 Ultra
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| Posted: Tue Oct 23, 2012 2:59 pm Post subject: |
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Hi,
First of all I'd say that IC601 is an optional component and if it's there it is part of the "sound-chain". If all the parts with asterisks (*) would be populated, this would mean that IC601's inputs would be connected to its outputs through R604/R614. So it's either the IC or the resistors and this can be seen on the difference list on sheet 1 (lower right corner). But that's only an interesting bit of information without relevance.
Interestingly, all three possible culprits (IC251, AV selector / IC621, Volume control / IC801, Component video switch) are controlled via I2C over the same lines called SDA2/SCL2. These two lines are connected to the ATSC tuner too, but this connection is controlled via Q001/Q002. Those two will connect to the ATSC Tuner as soon as the 3.3V supply is present. So I would check this first. Intermittent outages could provoke nonsense on the I2C bus which the could cause the symptoms.
Usually You would expect some kind of control via I2C coming from an system controller (IC701, Main CPU). On this schematic this doesn't happen. IC701 only controls SDA0/SCL0 and SDA1/SCL1. I'ts not clear to me where control over SDA2/SCL2 comes from. Maybe this is part of the problem...
Regards,
barclay66
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Oct 23, 2012 3:00 pm Post subject: |
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| Curt Palme wrote: | It's a trick question.
Answer: It's a digital. Not worth repairing, throw it out.
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Ha, it's a CRT RP. Otherwise I'd fix it with a hammer......
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