Re: [AH] TR 707 repair

From Kenneth Balys
Sent Fri, Mar 7th 2014, 00:58

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:
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> 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
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> 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.
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> I think its
> in your reset circuit, attached page.
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> 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]
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> Sent: March-06-14 12:18 AM
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> To: luke aldred
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> Cc: Lorne Hammond; analogue@hyperreal.org
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> 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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> On Mar 6, 2014, at 3:12 AM, luke aldred <laproductions@live.com.au>
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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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> From: lhammond@uvic.ca
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> To: laproductions@live.com.au; analogue@hyperreal.org
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> Subject: RE: [AH] TR 707 repair
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> 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]
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> Sent: March-05-14 10:00 PM
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> To: analogue@hyperreal.org
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> 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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