Re: [AH] TR 707 repair

From Kenneth Balys
Sent Fri, Mar 7th 2014, 01:05

Duh! I mean is the Reset line stable and high after power up?

(why does my brain always take off right when I need it?)

On 06.03.14 11:58 PM, Kenny Balys wrote:
>
> The reset line is held low by the "power good" circuit until it hits the
> operational threshold. This is done so the CPU does not kick off during
> the chaos of power on.
>
> The reset line is NAND'd to the -CS (chip select) of the two static RAMs
> as they are battery backed and contain your pattern data. So you do not
> want random stuff happening. The -RESET prevents anything from getting
> to the RAM chips.
>
> I don't know the pinout of the 707 cartridge but the -RESET to the
> buffer IC7 is going to be protecting something as well.
>
> The 138 Mux just takes a 3 bit number on one side and activates the
> correct line on the other (0 to 7) when the 3 enable lines are SET/CLR/CLR
>
> Is your reset line stable and low after power up?
>
>
> On 06.03.14 11:15 PM, luke aldred wrote:
>>
>> Hey Lorne,
>> I don't know much about these CPU circuits, but I assumed the reset
>> signal here turned on the chip select data outputs from IC16 so that
>> RAM can be written only after reset signal. Not sure though as I say.
>> Thanks again
>>
>>
>> From: lhammond@uvic.ca
>> To: wackyvorlon@me.com; laproductions@live.com.au
>> CC: analogue@hyperreal.org
>> Subject: RE: [AH] TR 707 repair
>> Date: Thu, 6 Mar 2014 06:57:38 -0800
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>> Paul:  I noticed this off the block diagram, any thoughts on
>> which pin for the other resets?
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>> the block
>> diagram shows the reset circuit (Q4, Q5) goes to the cpu IC5, the address
>> decoder IC 16, and Buffer IC7.
>>
>> I think its
>> in your reset circuit, attached page.
>>
>> Any thoughts on the reset pins for teh other ICs?  Or why they
>> reset, unless its to sync them all when the voltage is correct.
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>> Lorne
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>> From: Paul Anderson [mailto:wackyvorlon@me.com]
>>
>> Sent: March-06-14 12:18 AM
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>> To: luke aldred
>>
>> Cc: Lorne Hammond; analogue@hyperreal.org
>>
>> Subject: Re: [AH] TR 707 repair
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>> It looks like IC11 is a de multiplexer. Here is the data
>> sheet:
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>> http://pdf.datasheetarchive.com/datasheetsmain/Datasheets-110/DSAP002952.pdf
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>> Look at pins 4,5, and 6. If 6 is low, or 4 or 5 are high,
>> then all outputs are pushed high. Including pin 13 which feeds IC16
>> via IC12.
>> The gate on IC12 is configured as an inverter. A high from IC11 pin 13
>> would be
>> low at IC16, holding the output low without regard for the inputs to
>> IC11. I'd
>> say something is making one of those three pins on IC11 sit at an
>> inappropriate
>> level.
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>> --------
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>>
>> Paul Anderson
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>> Facilities Manager
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>> Hackforge
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>> On Mar 6, 2014, at 3:12 AM, luke aldred <laproductions@live.com.au>
>> wrote:
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>> Hey Lorne,
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>> Thanks again. I can't tell on which pin the reset signal should
>> be on IC7, but in all other locations it is good. IC7 is a buffer for the
>> Cartridge storage, so would it even make a difference? I have the
>> cartridge
>> ribbon unplugged anyway.
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>> As for Kenneth Bayes notes, I was noticing small pulses on
>> ground connection, though they are less than 100mv so I wasn't
>> worried. Would
>> this cause dramas?
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>> Paul, thank you for your input. Pin 10 is connected directly to
>> pin 4, this is the reset signal. Pin 11 is connected to Pin 3, and pin
>> 12.
>> These are fed by an output from IC11. Address data of some sort?
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>> Luke
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>> From: lhammond@uvic.ca
>>
>> To: laproductions@live.com.au; analogue@hyperreal.org
>>
>> Subject: RE: [AH] TR 707 repair
>>
>> Date: Wed, 5 Mar 2014 22:40:32 -0800
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>> Don't know the machine but I do know the 909 has a reset that
>> stays low and off until there is 5V stable top prevent scrambled memory.
>> So you can have the right voltage at teh power supply but if you reset
>> circuit
>> has a broken trace or dead transistor (on the 909 that is on the PS
>> pcb) it
>> will not allow the cpu to start up.
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>> lorne
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>> om: luke aldred [mailto:laproductions@live.com.au]
>>
>> Sent: March-05-14 10:00 PM
>>
>> To: analogue@hyperreal.org
>>
>> Subject: [AH] TR 707 repair
>>
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>> Hi all,
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>> I have a
>> TR-707 here which I'm repairing. It does not power boot up. Power supply
>> voltages etc are all good, and scoping the CPU I can see data on the
>> address
>> and data buses.
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>> When scoping
>> around the RAM chips, I found that the Chip Select pin (pin 18) for
>> RAM 1,
>> IC14, is sitting on between 4.5-5V. When I look at the same pin on
>> IC13 I can
>> see the chip select data flowing. Now I assumed that the chip address
>> IC 16 may
>> be faulty, so I swapped it out to no avail. Strangely I then noticed
>> when I
>> bridged pins 8 and 9 on IC16 (TC40H010) the unit fired up for the
>> first time.
>> It was mostly functioning, I could hear sounds, swap patterns etc
>> though it
>> seems I could not write any patterns and it was still a bit glitchy in
>> general.
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>> Anyone
>> got any ideas what else this may be? I have tried new RAM in both
>> positions to
>> no effect, have also tried a new IC11. I wonder if it could be the
>> program ROM
>> or CPU error?
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>> Thanks
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>> Luke
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