[QuadList] AVR 2 TBC Problem

Fri Nov 20 11:28:30 CST 2015

Ken,

Thanks for getting in touch and for sharing your wisdom, I've looked at
your website a few times and enjoyed the details/ photos on the refurbs
you've undertaken.

I certainly found problems on the 2 line delay that I thought I'd nailed.
If there is subcarrier clocking on the output bits then I should
investigate the waveform on the pins of the boards more closely than I had
been and trace back to where that's getting in.  It makes sense that it may
on the Memory board and that the 3 bits originally absent on the 2 line
delay board were a separate issue, what I am now seeing could be another
issue just passing down the chain.. When I was working on the TBC on
Wednesday it looked like another bit failed mid afternoon.at which point I
despaired as I knew all hope had gone of fixing the machine before I had to
leave. Very disappointing and frustrating.

The AVR is out in Singapore and, unfortunately, I ran out of time as I had
to fly back to London yesterday. The distinct likelihood is that I'll be
going back out again. The original fault was "smoke" that I traced to the
audio board tantalems, nobody mentioned any other issue or fault (of course
!). On Monday I'll try to explain to my boss that 'in their day' this is
why VTR's were driven by engineers and that fixing these issues pre-date
today's board swap method of repair.

I'm very grateful for you taking the time to respond.

Best regards,

David Willis

On 19 November 2015 at 21:32, Kenneth Zin via QuadList <
quadlist at quadvideotapegroup.com> wrote:

>
>
>
> ---------- Forwarded message ----------
> From: Kenneth Zin <kenrzin at gmail.com>
> To: Quad List <quadlist at quadvideotapegroup.com>
> Cc:
> Date: Thu, 19 Nov 2015 13:32:22 -0800
> Subject: Re: [QuadList] AVR 2 TBC Problem
> David, look at the frequency of the bits, are they  (4.43Mhz or 13.3Mhz)
> all of the memory is clocked at subcarrier.
> If you have all of the twenty four bits, make sure that there is no
> clocking in the output bits, just clean hi or low.
> look's like the third bit ( counting from the MSB down) is the fault.
> either memory or two line delay would be my guess.
>
> Regards,
>
> Ken Zin
>
> On Tue, Nov 17, 2015 at 3:08 AM, David Willis via QuadList <
> quadlist at quadvideotapegroup.com> wrote:
>
>>
>>
>>
>> ---------- Forwarded message ----------
>> From: David Willis <david.willis at tvt.biz>
>> To: quadlist at quadvideotapegroup.com
>> Cc:
>> Date: Tue, 17 Nov 2015 11:07:51 +0000
>> Subject: AVR 2 TBC Problem
>> Hi,
>>
>> Currently working on an AVR 2 (it's been a while since I last worked on
>> one of these) that's got a TBC problem. I tracked down and replaced the
>> dead chip (A32) that fed clocking to registers at the front of the D-A and
>> found the non working chips (A4 and A56) on the two line delay that I
>> replaced with working spares from a non working board. I appear to now have
>> all 24 bits going into the memory, out again, through the 2 line delay and
>> into the D-A however please see attached photo of TBC out when fed with the
>> ramp from Bd 17. It appears I'm still missing bits.
>>
>> Fortunately I have some spare boards and have tried swapping out the A-D,
>> Clock Gen and Burst Store Gen in turn each with no change. I don't have
>> another working D-A. For info I've got the TRW A-D with associated bypass
>> board.
>>
>> The machine is better than when I started but not yet fit. If anyone with
>> greater experience has any ideas where I should be looking I'd be grateful
>> for the advice.
>>
>> Thanks.
>>
>> David
>> Engineer, TVT
>>
>> [image: Inline images 1]
>>
>>
>>
>> ______________________________________________
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>>
>> Change subject to reflect thread direction. Thanks.
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>
> ______________________________________________
> Please trim posts to relevant info when replying.
>
> Change subject to reflect thread direction. Thanks.
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