Breadbin Repair - Black Screen

[+DrVenkman]

Okay, AtariAge Hive Mind - I need your help.

 

I have a Breadbin that got zapped inadvertently (by me!) two summers ago when I pulled it out of storage after 12 - 13 years. The black brick PSU had gone bad over time and killed the machine. Both were working when stored years ago but we know how that goes. Too bad I didn’t realize the brick PSU’s were as dangerous as the Atari Ingots. Oh well. 

 

I got a new bare-bones PSU from Ray Carlson and it works fine with my still-working 64C. So I plugged it into my Breadbin and powered it up. First thing I noticed was that one of the DRAMs was scorching hot - clearly shorted internally. I replaced that this morning (I love my Hakko FR301) without a problem - no traces or pads damaged in the process. But still no boot. 

 

Here’s what I’ve done: I’ve verified both the 6510 and VIC-II have good Vcc and Vss. I’ve measured what appear to be a good color/sync and good luma signals on the VIC-II pins 14 and 15. I’ve verified good clock in and out from the 6510, and good activity on pins of the data bus at the 6510. Most of the address bus pins are pulsing nicely but the waveforms are “different” at one or two of them. However, knowing very little about the 64 architecture, I don’t know if those lines correspond to high bit addresses or something and so they’re accessed more rarely with the machine at idle. 

 

So next steps, anyone? 

 

(Photos below are of the “scorcher” removed and the replacement socket soldered in and chip inserted).

 

 

Edited July 24, 2019 by DrVenkman
typos

[motrucker]

Have you checked all of the RAM chips? It's not uncommon for a bad PSU to take them all out. Also check the PLA

If we knew the motherboard version it might help too.

 

 

[shoestring]

Check the other ram chips as well.  There's also two ram address multiplexers at U13 and U25 ( MOS 7708 ) which are identical to the 74LS257.

 

Other things to check.

 

1. PLA

2. Kernal rom.

3. Try a cartridge if you have any

4. Signals to the 6510 ( NMI and IRQ ).

5. VIC-II

 

 

 

 

 

[+DrVenkman]

Thanks for the further feedback. I’ve replaced the 7708’s with a pair of new 74LS257’s but no change. I’ve got good scope traces on the memory bus, the 6510 and VIC-II. I don’t have a compatible VIC to swap in so that will have to wait for now.

The CIA and ROM’s are soldered except the character ROM. I can remove and socket them but I’d rather avoid that for now since I don’t have replacements for them anyway.

I’ve also got a PLA replacement and a dead-test cart on the way. With luck I’ll get more info soon.

[shoestring]

There are some additional things you could try using Ray Carlsen's page as a reference / guide.

 

http://personalpages.tds.net/~rcarlsen/cbm/c64/c64blank.txt

 

As you can see a lot of things can cause a black screen.. even a bad SID or shorted CIA. 

 

Good luck, but I am sure you'll get it working soon.

[+DrVenkman]

On 7/6/2019 at 3:05 AM, shoestring said:

There are some additional things you could try using Ray Carlsen's page as a reference / guide.

 

http://personalpages.tds.net/~rcarlsen/cbm/c64/c64blank.txt

 

As you can see a lot of things can cause a black screen.. even a bad SID or shorted CIA. 

 

Good luck, but I am sure you'll get it working soon.

Thanks, I’ve been digging through the tips on Ray’s site, as well as watching a ton of black screen repair videos on YouTube. 

 

The SID on my board is socketed so it’s been removed since initial testing. The CIA ships are not socketed though I’m tempted to remove them and install sockets while I’m at it. I have not yet done that. I also haven’t swapped  out the rest of the DRAM chips - I don’t look forward to socketing 7 more chips potentially unnecessarily. I’ll wait for the arrival of the Dead Test Cart before I take that step, as well as the PLA replacement. With luck, the new PLA will fix the machine, and if not, hopefully the Dead Test Cart will give me a bit of insight.

[ChildOfCv]

If you have an Arduino handy, you could also build a tester.  This dude claims to have a few designed.

https://www.lemon64.com/forum/viewtopic.php?t=65187

[+DrVenkman]

32 minutes ago, ChildOfCv said:

If you have an Arduino handy, you could also build a tester.  This dude claims to have a few designed.

https://www.lemon64.com/forum/viewtopic.php?t=65187

As it happens, I have an UNO, a breaboard, a ZIF I can use for testing, and a whole mess of jumper wires. So that looks like a fun project. If the modern PLA replacement doesn't get it done, I'll likely build that tester. Of course, the Dead Test Cart is already paid for and en route, so that'll help.

 

I did do some more testing today while I wait. I think it's pretty clear my PLA is dead. There's lots of activity on the address bus inputs to the chip, but the CHAROM, KERNAL and BASIC outputs are nowhere near where they should be, per the schematics in SAMS COMPUTERFACTS.

 

Expected signals on these three outputs:

 

 

What I actually see on pin 16 for the Kernal ROM (measured with the probe right on the chip shoulder - note the amplitudes of all signals):

 

 

Pin 15, the Character ROM:

 

 

And pin 17, the BASIC signal (should be held high):

 

 

[ChildOfCv]

Yep, the PLA is a common problem.  According to someone (maybe even the designer of C64 himself), Commodore didn't do the passivation on the PLA chips correctly, so it's not a matter of "if" the chip fails, but "when".

 

Also, don't use the ROM method of replacing the PLA.  It causes bus contention which is easily seen when Zaxxon freezes just as the first wall appears.  I believe there's someone out there who has recreated proper PLAs which don't have the self-destruction issue, and work perfectly.

[motrucker]

Did you order the test harness with your dead test cartridge? Without the harness it will not tell you a lot.

ps - The PLAnkton replacement PLA is the best choice out there. It works with everything and gives off no heat!

 

 

Edited July 8, 2019 by motrucker

[shoestring]

On 7/7/2019 at 7:02 AM, DrVenkman said:

As it happens, I have an UNO, a breaboard, a ZIF I can use for testing, and a whole mess of jumper wires. So that looks like a fun project. If the modern PLA replacement doesn't get it done, I'll likely build that tester. Of course, the Dead Test Cart is already paid for and en route, so that'll help.

 

I did do some more testing today while I wait. I think it's pretty clear my PLA is dead. There's lots of activity on the address bus inputs to the chip, but the CHAROM, KERNAL and BASIC outputs are nowhere near where they should be, per the schematics in SAMS COMPUTERFACTS.

 

Expected signals on these three outputs:

 

 

What I actually see on pin 16 for the Kernal ROM (measured with the probe right on the chip shoulder - note the amplitudes of all signals):

 

 

Pin 15, the Character ROM:

 

 

And pin 17, the BASIC signal (should be held high):

 

 

Those are the /CE ( chip enables ) lines to the three roms.

 

Guarantee the other signals to the VIC-II will be funky as well.

 

Definitely a bad PLA.

 

 

 

[shoestring]

On 7/7/2019 at 2:00 PM, ChildOfCv said:

Yep, the PLA is a common problem.  According to someone (maybe even the designer of C64 himself), Commodore didn't do the passivation on the PLA chips correctly, so it's not a matter of "if" the chip fails, but "when".

 

That was Bil Herd, the C128 designer. The TED machines had the same issues. He's done a lot of talks about the process they used to manufacturer those chips.

 

The other issue was high power dissipation on a small die area which sped up the aging of the PLA.

 

I believe it was the early PLAs that had this problem from 82-83. Not sure about later batches.

 

http://skoe.de/docs/c64-dissected/pla/c64_pla_dissected_a4ds.pdf

 

Edit:

 

You can also use a PLS100N which run much cooler and more reliable. Commodore originally used 82S100 before going to the mass produced mask version ( 906114-01 ).  

Edited July 8, 2019 by shoestring

[+DrVenkman]

The PLA in this machine is from week 20 of 1984 but as you can see from the scope traces, it’s decidedly not well.

 

Of course this board also had a dead-shorted DRAM chip that was scorching hot. I removed and socketed a replacement and I’m getting good activity on the address and data lines for all the chips. 

After I get the PLA taken care of, I’ll see if there are any other issues that need addressing. 

In the meantime, my 64C is doing fine with one of Ray’s replacement PSU’s and I’ve got a Pi1541 coming today to sit on top of a spare RPi3 I have here already. So I’ve got a working system to play with while I continue working on this Breadbin. 

[shoestring]

My bread bin has one from 88 ( 2488 21 ). Obviously, this was completely rebuilt with sockets at some point before I bought it in 2007.

 

I recently added a bunch of heatsinks to all the major chips ( 6510, PLA and SID ), it should help but I'm not counting on it to save the PLA from certain doom.

 

 

[+DrVenkman]

Alright, I got a replacement PLA in today (a "PLAnkton" - not sophisticated enough to know the difference between the various replacements but anyway ...). I installed it into the new socket and progress!

 

 

This is still decidedly better than a completely black screen, as it at least confirms both the RF modulator, VIC-II and video out circuitry are okay. The Dead Test Cart is giving me one flash, repeating. So dead DRAM at U12, I think. I'll remove, socket and replace that one next later in the week. 

[+DrVenkman]

After work tonight I decided to mess with my "Deadbin" ...

 

So the Dead Test Cart gives me one flash, repeating. For this revision board that indicates a fault with U12, another 4164 DRAM. Out comes the Hakko and in a few minutes, out comes the suspect chip. In goes a new DIP-16 machine pin socket and a 4164 salvaged from my parts bin (originally in my Atari 130XE).

 

 

 

 

Dead Test Cart inserted, power on and .... SUCCESS! Well, mostly.

 

 

 

The machine still has a couple issues. First and most obviously, I have a dead SID *sniff sniff* eBay shows replacement 6581's are going for $50 - $80. Whew. Okay then. The next problem is that there are some keyboard issues, I think. The keys all seems to work, but the cursor keys don't actually move the cursor. They give me some inverse alphabetical characters. Also, pressing RUN STOP - RESTORE doesn't seem to do anything. I think I'm getting some spurious key-presses there too, but not sure if I'm remembering right. So probably a bad CIA at U1. I haven't yet tried serial port stuff with the drive or Pi1541, but that's in store for later this week. I see 6526's are getting expensive on the 'Bay as well. Bleh.

 

Anyway, progress ...

 

EDIT: Cleaned the shit out of the keyboard connector pins with Deoxit and tried again. Suddenly my cursor keys and whatnot seem working. Whew. I will test serial I/O tomorrow after work.

[shoestring]

Looks like you're on to it.

 

Other parts you can search for are. 6526A, 6526B or 8521 ( hard to find ).

 

For troubleshooting, you could use some 8520s from an A500 ( if you have one ) temporarily and those will work for the most part. Not recommended though as a perm fix.

 

 

Edited July 18, 2019 by shoestring

[+DrVenkman]

6 minutes ago, shoestring said:

Looks like you're on to it.

 

Other parts you can search for are. 6526A, 6526B or 8521 ( hard to find ).

 

For troubleshooting, you could use some 8520s from an A500 ( if you have one ) temporarily and those will work for the most part. Not recommended though as a perm fix.

I don’t have an Amiga 500 as a chip-donor for testing but after cleaning the crap out of the keyboard connector, the keyboard is fully functional. I have not tested serial I/O yet but I have a working 1541-II drive and a Pi1541 I can use for that later in the week or this weekend.

The biggest issue is the apparently-dead SID. I have good voltages for Vcc and Vdd (5.01V DC and 12.04V DC respectively), and activity of some sort on all the address and data lines but no proper sound output. With my JUPITER LANDER cart, after a couple minutes of warming up, I get a continuous high-pitched oscillatory whine. Pretty sure that chip is dead. I’ve about decided to just buy a cheap Nano SwinSID this weekend for basic sound in games and call it good. I’ve got a fully-working 64C as well, after all. I’ve already socketed and replaced two 4164 DRAM chips, two MOS 7708 (74LS257’s), and the PLA. Thankfully the SID is already socketed so assuming whatever I buy has good connections on all pins I won’t need to remove and replace that socket (though I have DIP-28 pin machine sockets if that becomes necessary). I am going to buy a JiffyDOS ROM though and install a switch and socket so if I need to replace the stock single-wipe SID socket it won’t be that much additional trouble.

[shoestring]

Good choice. I think I'll be doing the same if the SID stops working in my breadbin and it's pretty close to the real thing, besides I don't have any use for paddles and mice.

 

 

[ChildOfCv]

I wonder if all of this was caused by the Power Brick of Death?  That's a lot of dead chips.

[shoestring]

4 hours ago, ChildOfCv said:

I wonder if all of this was caused by the Power Brick of Death?  That's a lot of dead chips.

On 6/30/2019 at 2:57 AM, DrVenkman said:

 

I have a Breadbin that got zapped inadvertently (by me!) two summers ago when I pulled it out of storage after 12 - 13 years. The black brick PSU had gone bad over time and killed the machine. Both were working when stored years ago but we know how that goes. Too bad I didn’t realize the brick PSU’s were as dangerous as the Atari Ingots. Oh well. 

 

 

 

 

I think that answers your question

 

Just like the Atari XL/XE power supplies, the 7805 is used in most of the c64 linear power supplies so the same failure modes.

 

I did have an old c64 supply that was getting really hot in summer, so I replaced the 5v circuit with an LM2956 DC-DC buck converter and added a 5.7v clamp circuit to it. I did the same to my XL/XE power supply.

 

 

Edited July 18, 2019 by shoestring

[+DrVenkman]

Yeah the original brick had worked fine when I got the machine 15+ years ago and when it went into storage a few years later. It died over time tucked away in a storage tote. After I determined the computer wouldn't boot after cycling the power switch a couple times, I realized the brick was crazy hot to the touch - like 127F or thereabouts when plugged into the wall and the temp measured with a thermocouple on my DMM. So yeah, I think the overheating PSU was clearly the cause of most or all of these issues - it was overheating because it had probably shorted internally - I shudder to think how much voltage slammed into the board.  I mean it’s possible one or more chips were just time-related failures while in storage but I tend to doubt it. 

Anyway, I’ll be ordering a Nano SwinSID tomorrow and hopefully the machine will be back in basic service. 

[+DrVenkman]

It looks like serial I/O and at least one joystick port are both functioning perfectly. So the dead SID seems to be all that's left to get replaced. I did order a Nano SwinSID today and I have a friend with probably over a dozen C64's who has indicated he'd be fine with selling me a replacement whenever he gets time to dig into them and confirm a working example to send.

 

 

ALSO: The Pi1541 is pretty great, but expensive by the time you add in the RPi3/3+ and PSU. It's too bad there's not an equivalent of something like the SDrive-MAX for A8 machines - but I like it. 

 

[shoestring]

Great! I don’t have the Pi1541 so I can’t comment. Generally,  any add ons for the c64 are expensive compared to Atari 8 bit stuff.

 

Im really happy with my 1541 Ultimate II+ cart. Does everything I need it to do and the SID emulation isn’t too bad. 

[+DrVenkman]

1 hour ago, shoestring said:

Great! I don’t have the Pi1541 so I can’t comment. Generally,  any add ons for the c64 are expensive compared to Atari 8 bit stuff.

 

Im really happy with my 1541 Ultimate II+ cart. Does everything I need it to do and the SID emulation isn’t too bad. 

The 1541 Ultimate II+ looked amazing but let's face it, I'm an Atari guy at heart. That's what I had as a kid and I've loved it ever since. Nostalgia is a hell of drug. 

 

I bought this C64 for my wife 15-16 years ago because my wife's brother had one and she used to love playing Jupiter Lander as a little girl. I picked up my 64C and matching 1541-II drive from a local Goodwill (<$20 for both) when that was still possible, just on a lark. I've already spent way more than these machines are worth to me personally to fix this one and make it usable again because, A) I love my wife; and B) I love screwing around with all kinds of vintage hardware almost as much as I love my wife. I get as much satisfaction from learning about and fixing broken things as in actually using them.

 

So, tl;dr: the Pi1541 drive emulator is probably gonna do me just fine, though I do need to put JiffyDOS into one or both of these machines if I want to ever really keep them out and usable full-time.