Re: Dead PET4032

[Adrian Graham]

Hi Tony,

On 05/10/2015 16:55, "tony duell"  wrote:

> And I would be surprised if you got nothing on the screen either. Odd bit
> rot would mean the wrong patterns for some characters. But still something.

The heater is working in the tube and now that I've got a proper DMM I'm
getting the correct AC voltage across pins 9&11 on the transformer.

Also the blue and brown pins look OK.
 
> This is presumably a large-screen machine with a 6845 on the mainboard.
> Is it initialising that (look at the vertical and horizontal sync outputs with
> your logic probe, are they toggling)?

No. Only HSYNC is toggling, VSYNC is low.

> Is it accessing the kernal ROM? Is the CS/ pin pulsing low?

Yes. The others are high.
 
> What about the RAS/ and CAS/ signals on the DRAMs?

RAS/ is toggling, CAS/ is high on all chips. VBB is -4.98, VCC is 5.08, VDD
is 12.02
 
>> A lot of the repair pages use a piggyback 6502/ROM/RAM add-in called a
>> PETvet but all I have is a DMM, logic tester and other working PETs as
>> sources of chips I can borrow.
> 
> I assume the logic tester is a simple logic probe and not a logic analyser,
> alas

I should receive an 8 channel logic analyser on Monday but for now I'm
getting results from the DMM and probe. Socket (empty) for UD11 looks faulty
in that it's VCC and GND pins show nothing. Continuity on the others looks
OK.

-- 
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?

Re: Dead PET4032

[Mike Stein]

- Original Message - 
From: "Adrian Graham" <binarydinosa...@gmail.com>
To: "General Discussion: On-Topic and Off-Topic 
Posts" <cctalk@classiccmp.org>

Sent: Monday, October 05, 2015 12:27 PM
Subject: Re: Dead PET4032



Hi Tony,

The screen's not connected, nor keyboard. I 
figured there was no point

until I got a chirrup.

My logic tester is a cheapo Micronta, yes. 
There's an unpopulated ROM
socket at UD11 so I can easily get +5 and GND 
from there for probing, I'll

do that tonight.

A


Is UD11 the only empty socket? If there's a chip 
in UD12 I'd remove it in case it's defective or 
has bent pins etc.; it'll be an option ROM of some 
sort.


Tony's right about the CG; it's not directly 
connected to the data & address busses so it's not 
likely to hang the system unless it's pulling down 
Vcc. I would connect the monitor though instead of 
just relying on the buzzer for signs of life; if 
there's any display at all it might give a useful 
clue.


I'd also check UD7 for poor contact or bent pins

Finally, I'd ask on the Vintage Computer Forum; 
even without me (;-) there are some very 
knowledgable PET folks there.


Good luck!

m



On 5 October 2015 at 16:55, tony duell 
<a...@p850ug1.demon.co.uk> wrote:



>
> One chip that does get hot is the Character 
> Generator at UA3 which I was
> going to swap with the one in my other 4032, 
> but that doesn't power up
> either. Presumably I can borrow one from a 
> 3032 or 8096?


A machine with a dead character generator ROM 
(unless it is so dead as to
pull a power supply line down) will still 
initialise. You would get the

warble.

And I would be surprised if you got nothing on 
the screen either. Odd bit
rot would mean the wrong patterns for some 
characters. But still something.


This is presumably a large-screen machine with 
a 6845 on the mainboard.
Is it initialising that (look at the vertical 
and horizontal sync outputs

with your
logic probe, are they toggling)?

Is it accessing the kernal ROM? Is the CS/ pin 
pulsing low?


What about the RAS/ and CAS/ signals on the 
DRAMs?


> A lot of the repair pages use a piggyback 
> 6502/ROM/RAM add-in called a
> PETvet but all I have is a DMM, logic tester 
> and other working PETs as

> sources of chips I can borrow.

I assume the logic tester is a simple logic 
probe and not a logic

analyser, alas

-tony





--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home 
computer collection?
www.binarydinosaurs.co.uk 

Re: Dead PET4032

[william degnan]

Look for inconsistencies in voltages and pulses to and from RAM.  You may
need RAM at the lowest memory locations to boot.  Hooking up the keyboard
at least to eliminate a missing keyboard as a reason the system does not
boot, and you can issue commands to search a disk drive even if the display
is faulty.  At least if you have a IEEE drive attached you can watch for
the the drive to respond when the 4032 is powered on, for signs of life
from the computer.

On Mon, Oct 5, 2015 at 1:40 PM, Mike Stein <mhs.st...@gmail.com> wrote:

> - Original Message - From: "Adrian Graham" <
> binarydinosa...@gmail.com>
> To: "General Discussion: On-Topic and Off-Topic Posts" <
> cctalk@classiccmp.org>
> Sent: Monday, October 05, 2015 12:27 PM
> Subject: Re: Dead PET4032
>
>
> Hi Tony,
>>
>> The screen's not connected, nor keyboard. I figured there was no point
>> until I got a chirrup.
>>
>> My logic tester is a cheapo Micronta, yes. There's an unpopulated ROM
>> socket at UD11 so I can easily get +5 and GND from there for probing, I'll
>> do that tonight.
>>
>> A
>>
>
> Is UD11 the only empty socket? If there's a chip in UD12 I'd remove it in
> case it's defective or has bent pins etc.; it'll be an option ROM of some
> sort.
>
> Tony's right about the CG; it's not directly connected to the data &
> address busses so it's not likely to hang the system unless it's pulling
> down Vcc. I would connect the monitor though instead of just relying on the
> buzzer for signs of life; if there's any display at all it might give a
> useful clue.
>
> I'd also check UD7 for poor contact or bent pins
>
> Finally, I'd ask on the Vintage Computer Forum; even without me (;-) there
> are some very knowledgable PET folks there.
>
> Good luck!
>
> m
>
>
>
>> On 5 October 2015 at 16:55, tony duell <a...@p850ug1.demon.co.uk> wrote:
>>
>> >
>>> > One chip that does get hot is the Character > Generator at UA3 which I
>>> was
>>> > going to swap with the one in my other 4032, > but that doesn't power
>>> up
>>> > either. Presumably I can borrow one from a > 3032 or 8096?
>>>
>>> A machine with a dead character generator ROM (unless it is so dead as to
>>> pull a power supply line down) will still initialise. You would get the
>>> warble.
>>>
>>> And I would be surprised if you got nothing on the screen either. Odd bit
>>> rot would mean the wrong patterns for some characters. But still
>>> something.
>>>
>>> This is presumably a large-screen machine with a 6845 on the mainboard.
>>> Is it initialising that (look at the vertical and horizontal sync outputs
>>> with your
>>> logic probe, are they toggling)?
>>>
>>> Is it accessing the kernal ROM? Is the CS/ pin pulsing low?
>>>
>>> What about the RAS/ and CAS/ signals on the DRAMs?
>>>
>>> > A lot of the repair pages use a piggyback > 6502/ROM/RAM add-in called
>>> a
>>> > PETvet but all I have is a DMM, logic tester > and other working PETs
>>> as
>>> > sources of chips I can borrow.
>>>
>>> I assume the logic tester is a simple logic probe and not a logic
>>> analyser, alas
>>>
>>> -tony
>>>
>>>
>>
>>
>> --
>> adrian/witchy
>> Owner of Binary Dinosaurs, the UK's biggest home computer collection?
>> www.binarydinosaurs.co.uk
>>
>
>


-- 
Bill
vintagecomputer.net

Re: Dead PET4032

[Adrian Graham]

> Is UD11 the only empty socket? If there's a chip
> in UD12 I'd remove it in case it's defective or
> has bent pins etc.; it'll be an option ROM of some
> sort.

Done, I'll see if my programmer can read it once my only working windows box
stops updating itself, sheesh.

> Vcc. I would connect the monitor though instead of
> just relying on the buzzer for signs of life; if
> there's any display at all it might give a useful
> clue.

Hm. Nothing at all from the monitor and checking the voltage at 10 + 11 on
the iron lump shows nothing - I didn't check them over the weekend as they
only run the monitor and the other pins seemed ok at 18 and 8VAC.
 
> I'd also check UD7 for poor contact or bent pins

Had that out earlier and it seems ok.
 
> Finally, I'd ask on the Vintage Computer Forum;
> even without me (;-) there are some very
> knowledgable PET folks there.

OK :)

-- 
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?

Re: Dead PET4032

[Adrian Graham]

On 05/10/2015 19:52, "william degnan"  wrote:

> Look for inconsistencies in voltages and pulses to and from RAM.  You may
> need RAM at the lowest memory locations to boot.  Hooking up the keyboard
> at least to eliminate a missing keyboard as a reason the system does not
> boot, and you can issue commands to search a disk drive even if the display
> is faulty.  At least if you have a IEEE drive attached you can watch for
> the the drive to respond when the 4032 is powered on, for signs of life
> from the computer.

I can try that, though there may be similar bitrot in my drives since
they've not been powered up for 10+ years...

-- 
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?

Re: Dead PET4032

[Ethan Dicks]

On Mon, Oct 5, 2015 at 2:52 PM, william degnan  wrote:
> Look for inconsistencies in voltages and pulses to and from RAM.

Yep.

> You may need RAM at the lowest memory locations to boot.

Absolutely.  The startup routines will be unhappy if zeropage is not there.

You can check for -5V as well, since the 4116 DRAMs need that.
There's a small circuit on the board with a 7905 to produce that.

>  Hooking up the keyboard
> at least to eliminate a missing keyboard as a reason the system does not
> boot

Nope.  As Tony Duell mentioned, it's a passive matrix.  The system
will not notice a missing keyboard.

> and you can issue commands to search a disk drive even if the display
> is faulty.

You can issue disk commands headless, but if you don't get the piezo
"twiddle", you probably aren't getting through POST to a READY prompt
anyway.

You _could_ be at a TIM prompt, I've seen that for some flavors of
broken PETs.  The video works, but something is bad in RAM or ROM to
screw up BASIC initialization.

> At least if you have a IEEE drive attached you can watch for
> the the drive to respond when the 4032 is powered on, for signs of life
> from the computer.

The machine does not autoboot.  The only signal that can affect the
disk drive is RESET, and that doesn't require the IEEE signals to be
initialized in software.

If you can get power to the video, you can pull the Chargen ROM and
you'll just see blanks for regular chars and solid blocks for inverse
video - like the cursor.

With the older models with TTL video circuits, they would display
chars if the ICs in the video section were working even if the CPU
wasn't, but the 4032 has a 6545 CRTC which is initialized by the ROMs.

On a machine that mostly worked but with dead video, I'd expect to see
strobing on the keyboard matrix every 1/60th of a second, and lots of
RAM and ROM enable strobing constantly.

One of the old hardware debugging tools was to take a real 6502 and
bend out the data pins and run wires from them to power and ground to
"spell out" $EA, for NOP (like this guy did...
http://www.grappendorf.net/projects/6502-home-computer/the-microprocessor).
Then back in its socket, the 6502 would run up the address bus and you
could watch the accesses flood over the address space, looking for
stuck select/enable bits

I have replaced dead 2114s (video SRAM), dead RAM (4116 DRAM and 6550
SRAM) and every once in a while, a dead ROM.  That's where I'd poke
around first, depending on what symptoms match what you are seeing.

-ethan

Re: Dead PET4032

[Adrian Graham]

Hi Tony,

The screen's not connected, nor keyboard. I figured there was no point
until I got a chirrup.

My logic tester is a cheapo Micronta, yes. There's an unpopulated ROM
socket at UD11 so I can easily get +5 and GND from there for probing, I'll
do that tonight.

A

On 5 October 2015 at 16:55, tony duell  wrote:

> >
> > One chip that does get hot is the Character Generator at UA3 which I was
> > going to swap with the one in my other 4032, but that doesn't power up
> > either. Presumably I can borrow one from a 3032 or 8096?
>
> A machine with a dead character generator ROM (unless it is so dead as to
> pull a power supply line down) will still initialise. You would get the
> warble.
>
> And I would be surprised if you got nothing on the screen either. Odd bit
> rot would mean the wrong patterns for some characters. But still something.
>
> This is presumably a large-screen machine with a 6845 on the mainboard.
> Is it initialising that (look at the vertical and horizontal sync outputs
> with your
> logic probe, are they toggling)?
>
> Is it accessing the kernal ROM? Is the CS/ pin pulsing low?
>
> What about the RAS/ and CAS/ signals on the DRAMs?
>
> > A lot of the repair pages use a piggyback 6502/ROM/RAM add-in called a
> > PETvet but all I have is a DMM, logic tester and other working PETs as
> > sources of chips I can borrow.
>
> I assume the logic tester is a simple logic probe and not a logic
> analyser, alas
>
> -tony
>



-- 
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk

RE: Dead PET4032

[tony duell]

>
> The screen's not connected, nor keyboard. I figured there was no point
> until I got a chirrup.

Well, if the piezo buzzer has failed But I guess that's not very likely.

-tony

RE: Dead PET4032

[tony duell]

> 
> One chip that does get hot is the Character Generator at UA3 which I was
> going to swap with the one in my other 4032, but that doesn't power up
> either. Presumably I can borrow one from a 3032 or 8096?

A machine with a dead character generator ROM (unless it is so dead as to 
pull a power supply line down) will still initialise. You would get the warble.

And I would be surprised if you got nothing on the screen either. Odd bit
rot would mean the wrong patterns for some characters. But still something.

This is presumably a large-screen machine with a 6845 on the mainboard. 
Is it initialising that (look at the vertical and horizontal sync outputs with 
your
logic probe, are they toggling)?

Is it accessing the kernal ROM? Is the CS/ pin pulsing low?

What about the RAS/ and CAS/ signals on the DRAMs?

> A lot of the repair pages use a piggyback 6502/ROM/RAM add-in called a
> PETvet but all I have is a DMM, logic tester and other working PETs as
> sources of chips I can borrow.

I assume the logic tester is a simple logic probe and not a logic analyser, alas

-tony