CBM 8032 - What does the startup chirp actually mean?

**MikeP** · November 1st, 2020, 12:35 PM

Hello Fellow Commodorians,

This is somewhat related to my previous post, but it just occurred to me that I don't know what that startup chirp from my PET means.

Is the chirp generated at a specific point in the boot-up sequence?
Can anyone tell me?

Thanks
Mike

**dave_m** · November 1st, 2020, 01:22 PM

Hi Mike,
It doesn't mean too much. The beeps go out very early in boot sequence. Five instructions in the subroutine cint (JSR $E000) is called which first calls cint1 (JSR $E60F) which inits the PIAs and the VIA, sets up some screen parameters and then gives a quick double beep.
The CTRC is not yet initialized nor is BASIC set up and memory test run.
-Dave

**MikeP** · November 1st, 2020, 03:39 PM

Hi Dave,

Maybe not the answer that I was hoping for, but still very helpful information.

Thank you!!!!
Mike

**daver2** · November 2nd, 2020, 12:26 AM

So, do you want to fix your PET then?

If you do, you have come to the right place!

What (if any) background in electronics do you have and what (if any) test equipment do you have (e.g. multimeter, logic probe, logic analyser, oscilloscope)...

People have fixed PETs with very little test equipment. Most of the faults can be relatively simple (faulty connection with a socketed IC or a duff socketed IC). Others can be a bit more complex and require the desoldering and replacement of one or more ICs. The odd few can be very tricky.

We are here to help if you want a go!

Where are you in the world? You never know, one of us could be near.

Dave

**MikeP** · November 2nd, 2020, 04:50 PM

Hi Dave,

Yes, I do want to fix my PET (for me, not so that I can sell it).

I have very limited background in electronics. I started by buying 3 dead commodore 64s and over a period of a couple of months, I was able to fix 2 of them. I have a multimeter which I am comfortable using, a logic probe, which I am somewhat comfortable with and I just bought a scope and I am trying to teach myself how to use that, but have not used it on the board yet. Also barely competent with a soldering iron (I plan to practice more on the C64s).

I have determined that the power is good (I checked the pins of one of the RAM chips and found that +12, -5 and +5 are good).

Two of the ROMs are actually EPROMS, one of which had nothing covering the window, so I'm guessing that might be corrupted.

I am located East San Francisco Bay Area. (But from the UK originally).

Cheers
Mike.

**dave_m** · November 2nd, 2020, 06:28 PM

Since you get the chirps, you may want to try daver2's diagnostic program that goes in the socketed UD7 ROM position. It will do a quick check of your RAM, ROM and keyboard. It does not depend on any good RAM or ROM. If you do not have the ability to burn a 2716 EPROM, I will send you a programmed chip (gratis) since you seem determined to fix your Commodore PET.

Here is the location of the PET 8032 schematics http://www.zimmers.net/anonftp/pub/c...iv2/index.html.
Check on sheet 1 that you get a good power-on Reset (/RES) at UD16-pin3. Upon power-on, it should pulse Low for 1/2 Second.

If you need the EPROM, send me a private message (on this forum) with you mailing address.

Daver2 and the other PET gurus on this forum will keep you on the right track.

**MikeP** · November 2nd, 2020, 08:56 PM

Thank you Dave,

I just checked Pin 3 on UD16 (NE555) using my logic probe.

When I powered on the PET, the pin was high then after about a second, it went low, but then it stayed low.
Any idea what this means?

**daver2** · November 3rd, 2020, 09:17 AM

Off we go with a new PET to resurrection...

First things first Mike.

To get the chirp means that we know that a few things are working:

1. The CPU. The chirp is produced by the CPU/VIA devices.
2. The first few instructions in the Kernal ROM (starting at $F000) are OK. The CPU reset vector is held in here - and the CPU executes a small number of instructions first within the Kernal ROM.
3. The Kernal ROM makes a subroutine CALL to initialise the PET hardware. This subroutine is located within the EDIT ROM (starting at $E000).
4. The chirp is produced by a combination of a tight software loop and the VIA timer/hardware. We know this must be good.
5. The CPU then goes into the 'weeds' somewhere after that.

The usual culprit here is BAD DRAM (especially in the critical area of Page 0 ($0000 .. $00FF) or Page 1 ($0100 .. $01FF). The stack is held in the latter area of memory.

First question - do you have anything at all on the screen?

If there is anything visible that would be a good clue. But (of course) the Kernal ROM code initialises the screen to <BLANKS>. So, if the EDIT ROM code has done it's job properly, there will be nothing to see on the screen!

Never fear, we can detect that by using a multimeter, logic probe or your newly acquired oscilloscope to have a look at the H and V DRIVE signals from the PET mainboard to the monitor.

Let us know the answer and we can go from there. Your posts will, of course, be moderated for a little bit - so just have a bit of patience...

Dave

**MikeP** · November 3rd, 2020, 09:27 AM

Thank you Dave for the detailed description of what the chirp means.
Regarding the display - absolutely nothing, not even that static feeling that you can feel near the surface. I did however look at the back and it has the orange glow.

Also there is the issue that the NE555 at UD16 does not seem to be behaving as expected (starts high, then goes low, but I gather it is expected to go high again which it does not do).

By the way, thanks for being willing to help - much appreciated.
Mike