Commodore PET 4032 no boot , no beep

[mjnurney]

now the CBM 4032 should beep (beeps) on boot , mine does not - in fact it does nothing.

The PSU fissed a bit but thats all , no display - no boot.

So PSU pinouts

AC

pin No
11) - 20.6 ACv
10)- na
9)-20.4
5)-gnd
8 )-18.61
7)-17.9
6)-8.6
4)-8.6

Video (on motherboard)
White - none
green - 3.82 Dcv
white - none
red - 4.4v
white- none
yellow - 0.38v

No boot noise or VDU display... although there is a quiet thud type noise like CRTs make when power is applied..

pin 1 is broke on the character generator ROM I've just noticed..

 

[mjnurney]

further investigation shows the PSU has blown apart the 240v inlet socket and thingy ma bob

 

[mjnurney]

Ive removed the HPF300CET unit and fitted a later more modern affair to it with a 0.1UF poly cap , the readings on the PSU are now slightly higher by 0.3v or so but still no boot.

The monitor is getting power as the tube is lit orange and makes a nice CRT noise..

i'll look at the ROMs next i suppose.

 

[rkauer]

Those ancient poliester capacitors are the same used in BBC & old Apple models with same bad behaviour.

Replace the whole shebang (as you already did) or fit new capacitors (with the same value, of course).

I don't know the correct output values for the PET power supply, but the values you are reading seems not right, as the PET uses normal 5V for logic.

 

[mjnurney]

It may well be 5v on the motherboard , some psu magic is soldered to the main board too .

These psu outputs seem very similar to another person pet I was reading about.

I have 5v on the motherboard and video socket I think.

 

[dabone]

The pet transformer provides the AC power for the regulators.
The regulators are located on the main board, in the large heatsink next to the transformer.


Come over to the vintage computer forum and ask about your pet there.
There are alot of us pet owners over there and plenty of help to be had.

http://www.vintage-computer.com/vcforum/forum.php


I've got a 2001-8 and a 4016 myself.

After you make sure your +5 is working correctly, the PETVet is a wonderful way to quickly eliminate ram and roms as the problem.

It's from the maker of the petdisk, I've got one and it's a ram/rom replacement board that fits into your cpu socket. It also has a debug mode and can dump the ram over a serial port.

http://www.bitfixer.com/bf/

Later,
dabone

 

[mjnurney]

oh excellent , i'll be popping over later

thanks for the info.

 

[TheCorfiot]

Did you ever get this working Mike..?

I have a 3032 now working perfectly...

And an 8032 which fizzed like yours and appears dead....
Yet all the correct voltages are being applied to the main board by the connector from the transformer cable.
The 8032 has two +5v regs the top one powering the Drams..it's input is 11VDC as expectec but it is not outputing anything..

Ok, lets replace the regulator, however when placing this 8032 board into the 3032 chassis it boots fine and beeps happily, the regulator is now supplying the 5V to the DRAMs...

Back in it's own chassis and the reg is 0v again icard

I have triple checked the wiring loom on both chassis and the voltages being fed by both transformers to the mobo connector is tge same :nuts:
I have changed the big smoothing cap but joy.

I am confused

 

[mjnurney]

its in the forgotten cupboard , i'll have to dig her out

 

[TheCorfiot]

Mike.
Dont fancy ripping out the transformer and cabling loom complete for a loan so I can try and. Find out where my problem is...

TC

 

[mjnurney]

next weekend ?

 

[Juri]

hello, i had the same problem with my Pet8032, the filter on ac power did exploded! replaced with a modern one pet was dead.. after checking with logic analyzer i found that 6502 died.. i replaced it and now work flawlwssly!!
if you have a spare 6502 you could give a try
Juri

 

[TheCorfiot]

next weekend ?

Marvelous....i really want to get this 8032 running as it's a beaut...

Cheers
TC

 

[TheCorfiot]

Well I'll be damned

I got the ole bugger up and running fine tonight.

Fitted a new 7805K reg (pinched from spares 1541 board)
and that brought her back to life.
Had to reduce the EHT voltage to the tube to remove the scan lines and the picture is nice sharply focused with good contrast..

And 4x 2114 SRAM video memory chips replaced to eliminate screen corruption when she warmed up.....

Works great, but needs a bloody good scrub

Looks like i'm sorted buddy but thanks anyway.....
TC

 

[protek]

Awesome work, Bas!

 

[iainjh]

Nice one bas!

 

[mjnurney]

hi guys ,

im all over this now ....

I've ordered some sockets for chip removal and ram tested (all soldered) I'm slightly conviced the PSU is outputting wrong ....ive ordered new regs to solve this i hope.

the 12v /5v is too high and the -5 is too low


I've also ordered the PETvet board to help with diagnosis.

mike

RAM 4116 pin1=-6.3v pin8=15.8v Pin9=6.45v Pin16=GND

Video ram - swapped for ZX ram - seems good.


motherboard to monitor
white=0
grn=6.39
white=0
red=5.88
w=0
yell=2.3

AC PSU


BL=13.55
BL=13.55
BLK=0
BWN=12.2
RED=0.44
BWN=12 OR 7 OR 3 (cycles)

CPU pin 8 =6.34v

The monitor occasionally has a light from the centre or a straight line top to bottom about 1mm wide and then fades to black , no beep from the buzzer on the pet.

I think something odd is going on with the PSU but I'm having trouble finding what they should be.

 

[sir_beaker]

 

[mjnurney]

I've changed the CRT control chip and now the monitor makes a pulsing noise - quiet but its a noise.


I now have two pulse signals on the motherboard header for the monitor.


No picture on screen or chirp from the motherboard yet but its progress i suppose. A picture on screen would be handy to see whats going on with the PET.

Also the voltages show above are a bit out, I've changed multimeter to a more accurate one.

ram -4.98 , 11.83, 5.06v

PSU
BLUE 16.62-16.64
BRWN 18.41-18.42

cpu pin 8 vcc 5.02v

VR2,VR3,VR4
5.75v
5.81v
9.71v

VR1
4.98v ,12.31v

monitor pinout

yellow 1.53v
white gnd
orange 4.58v
white gnd
green 4.8v
key
white gnd

So some progress , the crt controller is from an Apple II 80 column card so that was handy.

So the screen pulses but no picture yet....or chirp...

happy days

http://youtu.be/x6cqniWV4gc

 

[TheCorfiot]

Mike, have you checked the frequencies of the H and V signals from the CRTC.
This is an important step because it will tell you if you have CPU activity or not.