5 Oct
2015
5 Oct
'15
8:49 a.m.
Hi folks,
Some storage reorganisation last week uncovered a PET4032 I'd forgotten I
had. Spotless internally (I remembered why later) and glass fuse intact so
I attempted powerup. Nothing. No screen and no chirrup.
Google + schematics time. I've checked AC voltage at the iron lump and all
major chips + DRAM are getting the right voltages. The processor is
generating a clock signal at PHI2 (~2.7V), I've checked continuity of all
address and data lines for ROMs/processor/VIA/PIA. I can't check the
contents of the Kernal ROM since it's not socketed and my track record of
successfully removing big chips whole isn't good.
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 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.
Are there any more steps I can try before checking ROM contents becomes
necessary?
Cheers.
--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk
5 Oct
5 Oct
8:55 a.m.
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
9:27 a.m.
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 <ard at p850ug1.demon.co.uk> wrote:
--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk
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
10:40 a.m.
----- Original Message -----
From: "Adrian Graham" <binarydinosaurs at gmail.com>
To: "General Discussion: On-Topic and Off-Topic
Posts" <cctalk at 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
<ard at p850ug1.demon.co.uk> wrote:
--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home
computer collection?
www.binarydinosaurs.co.uk
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
11:52 a.m.
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.stein at gmail.com> wrote:
----- Original Message ----- From: "Adrian
Graham" <
binarydinosaurs at gmail.com>
To: "General Discussion: On-Topic and Off-Topic Posts" <
cctalk at classiccmp.org>
Sent: Monday, October 05, 2015 12:27 PM
Subject: Re: Dead PET4032
Hi Tony,
--
Bill
vintagecomputer.net
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 <ard at
p850ug1.demon.co.uk> wrote:
--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk
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
11:52 a.m.
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
The PET keyboard is just a matrix of switches, if nothing it pressed it tests as
an open-circuit between all pins. So the machine can't fail to start up because
the keyboard is not connected.
-tony
12:30 p.m.
On 05/10/2015 19:52, "william degnan" <billdegnan at gmail.com> 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?
1:55 p.m.
One chip getting hot does bother me.
Have you measured the voltage rails.
If the voltage is gone, it may be shorted.
Just swapping it out may not be a good idea unless
you know that it wasn't a failed regulator that
caused it to short out.
Some of the TO-3 type regulators depend on the
screws connecting the case to ground.
I have seen case that corrosion caused by dissimilar metals has caused
the case to float, causing over voltage and damage to the circuit.
I don't know that that is the case of a PET ( don't know
what they use for regulators ).
Voltage checks are always a first.
Dwight
1:05 p.m.
On Mon, Oct 5, 2015 at 2:52 PM, william degnan <billdegnan at gmail.com> 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
12:26 p.m.
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?
10 Oct
10 Oct
5:57 p.m.
Hi Tony,
On 05/10/2015 16:55, "tony duell" <ard at p850ug1.demon.co.uk> wrote:
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?
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
3360
days inactive
3366
days old
11 comments
7 participants
participants (7)
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ard＠p850ug1.demon.co.uk -
billdegnan＠gmail.com -
binarydinosaurs＠gmail.com -
dkelvey＠hotmail.com -
ethan.dicks＠gmail.com -
mhs.stein＠gmail.com -
witchy＠binarydinosaurs.co.uk