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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: Mon Jan 28, 2013 12:32 am Post subject: What am I doing wrong here? Marquee 8500 |
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I normally don't post schematics, but here's the video output stage of a standard 2035-02 VIM. I've got two here with identical problems- very low output on red on one, green on the other. THe other two channels are fine.
I've narrowed the issue down to the AD835 video output amp. Signal is fine going in, very little coming out. I ordered two new (very expensive, I might add) amps from China, so I put one in. Same problem. I'm not putting in the other one, as I don't buy that two amps would have the same issue. Voltages in and out are fine. I've paralleled the control pins between chips, to see if the red connection will bring down the blue for example, or if paralleling them will bring the red back. Nope, not unless I parallel the chip output, then the red comes on full with the blue output working fine.
So what the heck am I missing?
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Tim in Phoenix
Joined: 21 Oct 2006
Posts: 4409
Location: Phoenix
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| Posted: Mon Jan 28, 2013 12:39 am Post subject: |
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You are missing the point that VIMs are so cheep they are not worth fixing!
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Jan 28, 2013 12:52 am Post subject: |
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Scope pin 8 of each amp and see if there is a significant difference in the bad color one.
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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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: Mon Jan 28, 2013 3:10 pm Post subject: |
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Wow, that's the first time I've heard about taking out a chip while it's in circuit. They're supposed to be impervious to static zaps when installed.
Mac, yes, the input to the AD chip is fine, identical to the others, the output is almost non-existent compared to the others. I'm leaving this alone for the day, have Ultra focus boards to repair, but will try again either tonight or tomorrow. I think changing the chip again, maybe with one from a scrap board I have here will determine if the chip is bad.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Jan 28, 2013 3:28 pm Post subject: |
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Pin 8 is not your input signal, it is your gain control signal. Pin 1 would be your input signal. If you have been testing and comparing pin 8's then I would suggest testing and comparing pin 1's
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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: Mon Jan 28, 2013 3:35 pm Post subject: |
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Sorry, wasn't looking at the schematic. What I need to try and do is lift pin 8 rather than short it to an adjacent chip, and jumper the raw pin over. I'll get on this... later today.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Jan 28, 2013 3:38 pm Post subject: |
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Are these dip's or sop's?
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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: Mon Jan 28, 2013 5:45 pm Post subject: |
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DIPs
and the tech working on it is apparently a DIP-S.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Jan 28, 2013 5:53 pm Post subject: |
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Then surely you must have some DIP sockets there. Pop 1 or 2 in and make it easier on yourself.... 
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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: Mon Jan 28, 2013 7:47 pm Post subject: |
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Well that solves that one! Finally got annoyed with the two boards staring at me, and I swapped AD835 chips from one board to another. Sure enough, both chips from China were DOA.
Tech, not so suspect any more. The chips from China... DIE DIE DIE!!!
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Jan 28, 2013 7:50 pm Post subject: |
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| Curt Palme wrote: | Well that solves that one! Finally got annoyed with the two boards staring at me, and I swapped AD835 chips from one board to another. Sure enough, both chips from China were DOA.
Tech, not so suspect any more. The chips from China... DIE DIE DIE!!!
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How about that. Did you get them from 1 of our usual suppliers or off Ebay?
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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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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Jan 28, 2013 8:00 pm Post subject: |
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| Curt Palme wrote: | Might try installing the chips backwards...
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Or sure, blow up something else now. Do you want me to check availability with some of my suppliers?
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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: Mon Jan 28, 2013 8:01 pm Post subject: |
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Sure, Digikey wants $20.00.!!!
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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| Posted: Mon Jan 28, 2013 8:12 pm Post subject: |
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I actually need one too. I cannibalized an 02p VIM to replace the Longbows AD835.I lost the replacement that Mouser sent me.I couldn't wait for the shipment and used a spare 02p. I think it was more than 20 bucks when I looked for
one.
You Know I have a board that Dennis made to convert a 02p to a 03p since the 03p has the higher bandwidth AD834. I should try to
get that working.
Athanasios
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Jan 28, 2013 8:15 pm Post subject: |
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Request sent. I'll keep you updated.......
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Jan 29, 2013 2:31 am Post subject: |
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I have received a couple quotes back and the lowest so far is 11.30 each on a quantity order. New and original.
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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 Jan 29, 2013 2:56 am Post subject: |
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Cool. I only need about 5. As Tim said, spare VIMs are plentiful, and at $14 a chip landed, not to mention the $30 I spent on bad ones, it's hardly worth it..
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Jan 29, 2013 4:32 pm Post subject: |
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I got some more quotes in this morning and we are down to around 7.70 each for new ex stock. But you may have to buy a minimum or 10.
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