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9700VHZ option for the 9700K MIDI2CV8, burnt R52
http://www.paia.com/talk/viewtopic.php?f=4&t=41
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Author:  PAiA-Scott [ Wed May 20, 2009 11:00 am ]
Post subject:  9700VHZ option for the 9700K MIDI2CV8, burnt R52

Hello Danjel.

Thanks for your messages. I'm glad you're comfortable with building the extra VHZ option. Did you realize that operation is one way or the other though and that it isn't practical to change back and forth? Resistors on the 9700K are added and change with the VHZ (and the DAC Tune trim setting). This is the reason the rack-mount chassis was made to hold two.

Do you not have the complete schematic? It is the posted schematic that has the edge missing. I can send a scan of the complete schematic if you need it.
There might be a cv or trigger output op-amp stage that has failed and is causing more pull on the supply ( the TL 084 at IC 11 or 12), or, IC13 is now showing up as trouble due to any change that may have been made with the power to the unit? Note on the end of the attached pdf with power tips/suggestions, there is a note about cutting the trace to pin 7 of IC13 and jumpering it to pin 8 to ensure it doesn't get too much voltage and attempt to internally shunt the extra voltage. There are also notes about Rs 51 and 52 and their affect on the voltage to the analog circuits according to the external power source.

Is there anything in contact with the bottom of the board? We send some black foam to hold the ICs in the parts kit and once if not twice, I have seen builders make the mistake of using this to space the bottom of the board away from a metal chassis. It is conductive foam and like the inside of a resistor (as an aside, useful for force-sensing resistor projects when put between two conductors).

Thank you.

Sincerely, Scott Lee


Danjel van Tijn wrote:
> just a quick follow-up:
> On the scan of the schematic you sent me, parts are missing/cut-off on
> the right side so I can't see the complete circuit.
>
> I was wondering if it is ok to replace R52 with a 120ohm resistor
> instead of 100? I have a 0.5W 120R on hand that I could use.
>
> cheers,
> Danjel
>
>
> Danjel van Tijn
>
>
>
> On Tue, May 19, 2009 at 10:56 PM, Danjel van Tijn <danjel@gmail.com> wrote:
>
>> Hi Scott,
>>
>> Thanks for all the info! That is a simple enough circuit to build I
>> will just wire that up on a proto board.
>>
>> However there is another issue I need to deal with first. The last few
>> months the midi2cv8 has been intermittent at times. Today it stopped
>> working altogether. It still powered on but the self-test failed (the
>> gate voltages are just held on). When I opened it up I saw that R52
>> had completely burned out (it was literally just charred ashes). The
>> only thing I can think is that it should have been a higher power
>> rated resistor in its place (it looks about the size of 1/4w). Do you
>> have any idea what may have caused that to happen?
>> I will replace the resistor but hopefully no other components were
>> damaged as a result.
>>
>> cheers,
>> Danjel
>>
>>
>> Danjel van Tijn
>>
>>
>>
>> On Tue, May 19, 2009 at 8:21 AM, Scott Lee <scott@paia.com> wrote:
>>
>>> Hello Danjel.
>>>
>>> The 9700VHZ option is presently unavailable. We our out of stock on the
>>> printed circuit board item used for the option. It is likely a new
>>> converter will be introduced before we go back to the 9700VHZ option. The
>>> function exists within the EPROM Firmware; however it is only activated when
>>> the option printed-circuit-board is added. It wouldn't be too difficult to
>>> build one on a DIP IC experimenter's board and wire it in as a substitute
>>> VHZ option. The schematic and phantom image of the board is in the 9700K
>>> manual. The circuit uses a 4051 IC, some NPN transistors, resistors, and
>>> trims.
>>>
>>> You can scroll down to the second page of the MIDI2CV8 schematic and see the
>>> vhz circuit option here:
>>>
>>> midi2sch.pdf (application/pdf Object)
>>> <http://www.paia.com/prodimages/midi2sch.pdf>
>>>
>>> As an aside, if you need only a single set of control signals for a volt/hz
>>> device, FatMan features this type of output from MIDI sent to it--and is an
>>> analog synthesizer too.
>>>
>>> Thank you.
>>>
>>> Sincerely, Scott Lee
>>>
>>> Danjel van Tijn wrote:
>>>
>>>> Hi there,
>>>>
>>>> On the midi2cv8 page it mentions something about the V/Hz option for
>>>> controlling Korg synths. I could not see this available on any of the
>>>> pages and I was wondering if you still sell this?
>>>>
>>>> cheers,
>>>> Danjel
>>>>
>>>>
>>>> Danjel van Tijn
>>>> m. 604-773-2426
>>>> w. http://www.intellijel.com
>>>> w. http://www.myspace.com/intellijel
>>>>
>>>>
>>>>
>>>
>>>
>
>
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