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SuperKomet
Joined: 13 Dec 2021
Posts: 3
Location: Italy
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 Link Posted: Tue Dec 14, 2021 8:44 am Post subject: Sony D-50 CRT question |
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Hello everyone
My name is Marco from Italy. I'm new to CRT projectors, but my hobby of electronic is like 25 year old. So when a friend gifted me some faulty projectors I feel confident that I can troubleshoot some problems of them (at least, the basic ones). The projectors were an italian RCF LS-4000 (red CRT glass cracked, no glycol inside, I will fix it next spring), a Barco Vision 600S (syncro problems, replaced a lot of bad capacitors and now works fine) and a Sony VPH D-50 (no blue but test patterns are perfect, I plan to track down the signal on the A board with a scope and find where it disappears, I think one of he MAX4121 switches is faulty - but if someone has a new input card I'm interested)
My question is about these "chambers" on the top of each CRTs. I guess that these are a sort of expansion chambers for the glycol, but two of them looks good, the other one looks like is fall inside the metal housing.
Considering that this projector must be installed on the ceiling due limited space in my living room, is something that I must check for glycol leaks? Is a weakspot?
Thank you for your help 
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Dancrt
Joined: 16 Sep 2017
Posts: 69
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| Link Posted: Tue Dec 14, 2021 9:01 am Post subject: |
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I’d be interested to how you fix the D 50 I have a D 50 main board with similar problem I ended up buying another board from Curt to fix it I have a Barco909 now so I don’t use the d50 but would be good to know since It’s mint tubes so will be used by someone one day … 1080i with moome card and new capacitors on the pa board and you can get a pretty good picture on small screen was thinking good bedroom projector 
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SuperKomet
Joined: 13 Dec 2021
Posts: 3
Location: Italy
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| Link Posted: Tue Dec 14, 2021 9:16 am Post subject: |
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If I will fix it I will make a post about the repair, after checking the manual and reading this forum I started to think that these IC switch are a weakspot. I need to solder some wires to the checkpoints on the board for take measuerments, since for troubleshoot the A board you need two 96 pins extension boards and the price for each one of them is like 200$ on Ebay lol
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Dancrt
Joined: 16 Sep 2017
Posts: 69
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| Link Posted: Tue Dec 14, 2021 11:17 am Post subject: |
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Awesome
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Boet
Joined: 10 Jan 2012
Posts: 30
Location: Netherlands
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| Link Posted: Tue Dec 14, 2021 8:54 pm Post subject: Re: Sony D-50 CRT question |
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| SuperKomet wrote: | [...] a Sony VPH D-50 (no blue but test patterns are perfect, I plan to track down the signal on the A board with a scope and find where it disappears, I think one of he MAX4121 switches is faulty - but if someone has a new input card I'm interested)
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I have fixed exactly this problem on a forum member (Jantino) his board this year. The MAX4121 chips are your first suspect. You'll find them underneath the fan. While you're at it, remove the dust that has gathered under there and clean the fan. If the galvanised steel cover has started to rust, use sandpaper to clean the rust and use a bit of metal spray paint to cover the exposed steel.
You can remove the A board from the projector, and build your own power supply. It needs five different voltages, if I remember correctly. Else, you can perhaps solder 'measurement extension wires' to tactical places on the circuit board, but be careful of noise pickup which can damage the chips as well... those wires will be like antennas. So using (thin) coaxial cable is prefered. Audio wire will also do (coax type).
Connect a signal source to the blue input which has failed. Doesn't matter if it's video or just a simple oscillator, I used a DDS sine wave oscillator at 100 kHz. 1 Vtt max.
If you'll be repairing the A board with an external power supply:
This is from memory, cause it's been a while, but if you have the schematic you'll quickly see what I mean: the projector sends data "I want to select channel X" to the DAC chips on the input board. From the DAC you'll see signals going to transistors which pull a select-pin on the MAX4121 either high or low. You can safely (if you use the right spot!) manipulate these select-signals by simply connecting one of the pull-up resistors to ground, by soldering a wire between base or collector (I can't remember) and ground. You'll need to check the schematic for that. The MAX4121 datasheets will tell you which input 1/0 combination should lead to a certain switch behaviour.
If you need an address for the MAX4121, or would like me to have a look at the board since I've already built an external power supply for it, also feel free to shoot me a message.
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SuperKomet
Joined: 13 Dec 2021
Posts: 3
Location: Italy
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| Link Posted: Wed Dec 15, 2021 9:15 pm Post subject: |
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Yeah I suspect the MAX4121 too. The problem started with a low blue level and some retraces of the same color. Then it died. The previous owner already removed three of them ( IC1037, 1038 and 1039, fix/slot switch) and put bridges between input and output. My suspect is IC1020, blue RGB/Other switch. I will connect my Tek scope to test point 405 and see if I see the blue signal.
Main problem, I check on Mouser and I wasn't able to find replacement for these ICs, i bought five of them from Ebay and that auction was the only one for MAX4121
If in future these chips will not be available anymore I think that the only way is replace these and put briges between the desired input and the output...
Last edited by SuperKomet on Wed Dec 15, 2021 10:13 pm; edited 1 time in total
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Boet
Joined: 10 Jan 2012
Posts: 30
Location: Netherlands
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| Link Posted: Wed Dec 15, 2021 9:45 pm Post subject: |
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I bought them from a chip broker in Asia who still had a couple of 100 in stock, found them via UTsource.
In April this year I paid, according to my invoice:
MAX4121CSA(used), SOP8, US $3.50 each
Shipping Cost (DHL) US $17.39
"used", but they were new. I also don't believe the seller on top of the list desoldered and sorted 33948 of those chips. 
Prices seem to still be around the same level.
https://www.utsource.net/sch/max4121.html
More brokers with stock, but higher minimum order quantities:
https://www.digipart.com/part/MAX4121
I wasn't able to find other video switches with the same pin layout and internal structure either.
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