Dead PET4032

[Mike Stein]

----- 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:
>
>> >
>> > 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