Re: Black Widow Video Problem

You can't scope the output of the DAC pin 18 since it is a current DAC.
The first place where you can see the signal as a voltage swing is at
the output of the opamp directly following the DAC. This opamp is the
I/V converter. The switches and 1495's are just to invert signals and
correct bowing.

- Mendel

On 31-1-2012 22:17, Maxstang wrote:
> Great suggestion Bill! I'll borrow a scope.. One of these days I'll be needing to buy one of those! -M
>
> On Jan 31, 2012, at 12:48 PM, wboucher6@cogeco.ca wrote:
>
>> If you have a scope, you could connect it in X-Y mode right to the 6012 DAC chip outputs (pin 18) and see if the image
>> looks okay there. If yes, then try again after the B10/E10 switches just before the 1495's. The idea here to narrow
>> down which section to focus on.
>>
>> Bill Boucher
>>
>>>
>>> Thanks Douglas! That's an excellent suggestion about A/B11's output. I'd forgotten that detail…
>>>
>>> I checked the resistors after I switched the chip/socket at C12 and looked at the voltages and chip activity with a
>>> probe afterward and it looked fine. A/B11 also seems to be making the right noises (with the probe) but I do know
>>> from experience that they can have strange effects as they die (had a Tempest once with a completely mirrored image
>>> and it was the 1495. )
>>>
>>> The Y pot looks original. I'll meter it and see what I see. I get what appears to be y collapse or perhaps complete
>>> fold over if I adjust the pot too far in either direction. Within the small range of pot movement where there's no
>>> collapse, the Y image can be adjusted larger and smaller…if only a little bit. -M
>>>
>>>
>>> On Jan 31, 2012, at 10:30 AM, Douglas Gauck wrote:
>>>
>>>> It does look like a Y axis problem. My question was how the X correction coming out of A/B11, going into your new
>>>> main Y axis C12 could affect the output.
>>>> Since it's socketed, you can pull out C12 and then check all the resistors around it in circuit - all that voltage
>>>> in the area could have toasted one.
>>>> You should be able to adjust Y size from limit to limit without collapse. Or do you mean shrink?
>>>>
>>>> Since there's been prior work done on the board (and the pots are often abused) is it Y size the correct 10K?
>>>>
>>>> -Douglas
>>>>
>>>>
>>>> On Jan 31, 2012, at 12:37 PM, Malcolm Mackenzie wrote:
>>>>
>>>>> Thanks Douglas.
>>>>>
>>>>> The MC1495 at C12 has been socketed and replaced by me. That chip had been socketed before, but the contacts were
>>> shorted under the socket. I replaced the socket and chip and that's how I got the video to come up. I haven't
>>> replaced C11 as this problem appears to be in the Y channel, but I'll check into it.>>
>>>>> As far as I understand the pincushion correction 1495s won't cause this problem. I'll try to piggyback a new one on
>>> them to make sure.>>
>>>>> One added note. I've noticed that the y-size pot has only a very narrow range of adjustment. Too small and I have
>>> y collapse, too large, and y collapse. In the very middle of adjustment the pic stretches out to as it appears in the
>>> pictures I posted. Don't know if this helps anyone pinpoint it. -Malcolm>>
>>>>> --- On Tue, 1/31/12, Douglas Gauck<douglas@gauck.com> wrote:
>>>>>
>>>>> From: Douglas Gauck<douglas@gauck.com>
>>>>> Subject: Re: VECTOR: Black Widow Video Problem
>>>>> To: vectorlist@vectorlist.org
>>>>> Date: Tuesday, January 31, 2012, 5:49 AM
>>>>>
>>>>> The caps are just sauce for the goose; I'd say the next likely cause is one of the MC1495Ls... at C12. I'm not up
>>> to speed on how the others (A/B11 and A/B12) providing X and Y correction factor in.>>
>>>>> On Jan 30, 2012, at 11:19 PM, Maxstang wrote:
>>>>>
>>>>>> Thanks for the reply. TL082s have been checked and one replaced with no change. Voltages are good, but I
>>> haven't replaced the caps yet.>> >
>>>>>> On Jan 30, 2012, at 8:09 PM, Douglas Gauck wrote:
>>>>>>
>>>>>>> TL082 at D10 and/or D/E12?
>>>>>>>
>>>>>>> Also check the +/-15v and 6.8 volt supplies, and maybe give them new caps?
>>>>>>>
>>>>>>>
>>>>>>> On Jan 30, 2012, at 8:42 PM, Malcolm MacKenzie wrote:
>>>>>>>
>>>>>>>> Hi all. I've been working on a dead BW board and now have it at least showing video, but it's still distorted.
>>> AVG chip and socket, and vector RAM and socket are good. Anybody seen this before? It almost looks like vertical
>>> fold over and the image does expand and contract along the y axis. Self test video is similarly distorted but I don't
>>> get any reported errors other than pokey problems. Any input is appreciated. -Malcolm>> >>>
>>>>>>>> Photos are here:
>>>>>>>>
>>>>>>>> http://i122.photobucket.com/albums/o263/maxstang289/IMG_2612.jpg
>>>>>>>>
>>>>>>>> http://i122.photobucket.com/albums/o263/maxstang289/IMG_2611.jpg
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Received on Tue Jan 31 16:30:04 2012