C64 Wifi Modem

I had built a C64 Wifi Modem quite a while ago using the excellent post at the 1200baud blog. I used the very basic adapter board with it and it worked just fine.

More recently a more complex adapter board appeared for the ESP8266, so I thought I'd have a go at the new adapter board from Sven Petersen. It was a LOT more complex with some nice features thrown in.

You can see here the difference in complexity.  There are literally two parts on the old board if you solder the ESP8266 module direct to it. The new board has at LOT of new parts.

 

  

It was a really nice project to put together with excellent documentation from both sites on how to set it all up. As you can see it works wonderfully.
 

Building a modern TMS2532 drop in replacement ( 4K ROM )

I've bought a few 2532 ROM's on the net and haven't had much success with them.  The problem is they are a) OLD, b) require very high voltages to burn ( 19 up to 25V ) and c) modern cheap burners do not support them.

So I thought hey, lets have a go at making my own . . . and it works really well.

You can skip to the bottom for the PCBs, BOM and Instructions.

Picking likely candidate parts

The first thing I did was source some modern EEPROMS that I thought may work. I ended up getting some AT28HC64B EEPROMS. They are 5volt tolerant and can store up to 8K of ROM.

The second thing I got were some SOIC to DIP adapters to I could prototype and burn them and put on the 4K character ROM.

A really rough schematic 

The next thing to do was to see how I could convert the AT28HC64B to match the pin out of a 2532.  This is where data sheets are really helpful

Datasheet for AT28HC64B

Datasheet for 2532

In the end I came up with this.  I did make some tweaks but it's essentially it.  The main thing I did was ground OE in stead of tying it to CE.

Let's Burn!

The first thing I did was to just burn the C64 Character ROM to the chip.  I did have an El-Cheapo burner but opted to get a more expensive GQ-4x4 for better 2532 support.  It didn't burn my 2532 EPROMs, but I have a feeling they are not any good.

I decided to use the upper 4K of the ROMs.  The ROMS have addresses from 0 to 1FFF in HEX.  This means I can put the ROM in two places 0 to FFF or 1000 to 1FFF.

The chips burnt and read correctly the first go.  I was really impressed.

Making a 2532 EPROM

 The next thing to do was to actually make it a replacement for the 2532 EPROM.  I implemented my schematic on a breadboard. Then the big test.  Could I read it back off of the chip using the 2532 Device instead of the AT28HC64 Device.  I plugged it in and hey presto it worked.

I dumped it out as a bin and did a binary compare on the read image with the c64 character rom image and it was exact.

Hold on to your chair it's testing time

I was pretty scared plugging this contraption in truth be told.  In the end however it worked beautifully.

PCB Design

My aim here is to create PCB small enough to fit in a socket and not interfere with anything and to create an adapter board so you can reprogram it with ease.

Because it is an 8K EEPROM it would also be nice to be able to jumper the upper or lower 4K.

So here is my go at the 2532 PCB.  The pair of jumpers on the right select the upper or lower 4K.  The jumpers on the left are to put the EEPROM into Read only and Output mode.

You must remove all of the jumpers to write to the EEPROM via a special adapter which also uses the 3 pins at the top.

 

 

Here is the adapter board for programming. 

Now all I have to do is get them manufactured.  I have a few other opensource projects I'd like to build so I'll get an order ready to go for my prototype soon!

Making the adapter board

The PCBs have arrived.  I have enough parts to make the adapter board so lets make and test it!

The adapter board allows you to burn the EEPROM using the AT28HC64B board profile in your EEPROM burner, if you were to try to burn it as a 2532 it would just catch fire!

I've soldered it up using a ZIF socket like so.

It fits very nicely into the EEPROM burner and as I'm waiting for some more AT28HC64B's I've used my prototype version to try it out and it works very well.  I did have to slow down the burner to normal speed.  I think this is because the wires that connect to the breadboard are quite long.

I can't wait to try out the EEPROM board.

Building and testing the replacement TMS2532

Finally all of the parts have arrived, so lets build.

Reading, erasing and burning the EEPROM is done with the adapter board for an AT28C64 and none of the jumpers on.

When complete you can put on the jumpers and read the board directly as a TM2532 EPROM.

Once I'd finished confirming it in the burner it's time to try it out.  It works very well indeed.

Build it yourself

You use these projects completely at your own risk!

1) TMS2532 (AT28HC64B) modern replacement EEPROM

    Note:        You cannot burn this chip as a TMS2532, you must use the adapter to

                    burn it as a AT28HC64B.

                    When burning you must remove all of the shunts!!

    BOM

•     PCB available at PCBWay
•     1 x AT28HC64B
•     4 x 4.7K Ohm Resistors SMD 0805 ( pullup / pulldown resistors )
  
•     2 x 12 pin headers ++ ( 0.1" / 2.54mm )
  

•     4 x 2 pin headers ** ( 0.1" / 2.54mm )
•     3 x 2 pin shunts ** ( 0.1" / 2.54mm )

   

    ** Optional ( you can solder the shunts after burning instead if you like ).

2) TMS2532 (AT28HC64B) Adapter

    Notes :    This fits between the EEPROM burner and the modern

         replacement EEPROM so you can burn it as a AT28HC64B.

    BOM

•     PCB for Adapter at PCBWay
  
•     1 x 24 pin ZIF Socket ( or you can use an ordinary Socket ) ( 0.1" / 2.54mm )
•     1 x 4 pin header 90 angle ( 0.1" / 2.54mm )
•     1 x 3 strand Male <=> Female jumper wire ( 0.1" / 2.54mm )

Burning the EEPROM

1. REMOVE ALL SHUNTS from the TMS2532 (AT28HC64B)
2. Insert the Adapter into the burner
3. Insert the TMS2532 (AT28HC64B) into the Adapter
4. Insert the THREE Jumper wires from the Adapter into the TMS2532 (AT28HC64B).
5. Burn the ROM as a AT28HC64B.

    Remember this is an 8K EEPROM so your options are

• Join 2 4K ROMS together and burn 8K starting from 0000-1FFF
• Burn one 4K ROM in the LOW position from 0000-0FFF
• Burn one 4K ROM in the HIGH position from 1000-1FFF
  

    

    The three jumper wires bypass the pullup/pulldown resistors so it can burn properly.

    It should look like this picture.

Using the EEPROM

    Once you have burnt the EEPROM remove it from the burner and install the shunts

    You will see a block of 8 pins under the 3 pin programming jumper.

    You'll notice the text 4K H / L this is the top of the board.

    Holding the board with the text at the top the pin pairs are

High	Low	WE	OE
High	Low	WE	OE

    To use the EEPROM you must shunt either the High (1000-1FFF)

    or Low (0000-0FFF) Address but NOT BOTH.

    You must shunt both WE and OE.

    Your EEPROM is ready for use.

   

Alternative parts : New SRAM for C64C Short Boards

I've fixed quite a few C64C short boards now and nearly all of them have had bad RAM.  On Ebay the RAM for C64C's seems to be at a premium.  I got a great deal buying a RAM expansion board for a laptop with lots of socketed chips but was there a better alternate.

It turns out there is with Jamarju's c64-sram, SRAM substitute for C64C shortboards

So off to PCBway I went and grabbed some boards to test it out.

There aren't too many parts to this project which made it pretty simple to get going.  Probably the hardest bit was just getting the chips aligned on the pads.  After that I found if I was really careful I could just apply some flux and then very carefully drag solder down without tacking the corner pins first ( If it's your first time you should tack with chip down first to stop it moving ).

Although I did get a few bridges a bit more flux and some solder wick made clean up a breeze.

You can see in the middle the New vs the Old RAM.

  

My C64C boards nearly all have socket RAM now so I popped them out and jammed the board in and it worked first time. I quickly built a second one and that worked too.  I'm pretty happy about this project, a big thank you to Jamarju for sharing.

Maintenance : Recapping my Amiga 600's

Some time ago I bought some Amiga 600's.  Both were sold as not working.  One was actually completely fine, the seller didn't investigate it properly.  One has a memory fault which was fixed by bypassing a bit of corrosion on the board. However both of them are showing signs of leakage on the surface mount capacitors.  I've been putting it off but now I really need to do something before any real damage is done.

Firstly . . . STOP!

There are some little square metal cans on the board . . . don't get cleaning fluid / isopropyl anywhere near them . . . or you may be surface mounting a new composite video chip on your board.

More on this later.

Do your research / Buy the right tools

I've been looking at this for ages and I've watch twist methods, cut methods, solder iron wiggle methods and finally hot air rework methods.  The only one that appealed to me was the last one.  I didn't have a hot air rework station yet so I set about trying to find a good one.  I looked at the ridiculously cheap Atten right up to the Hakko, but in the end I got a Quick 861DW as recommended by Louise Rossman and later reviewed by Dave Jones.

I'm glad I did, using it made getting the SMD Caps off an absolute breeze.

Now putting back the Caps that was an issue.  Pretty much every video I watched only showed the Caps coming off.  No one actually showed them going back on.  This sort of concerned me as people showed everything up to putting the new Caps on and then bang, they were done.

I did experiment on a practice board putting on the Caps with the Quick, but I really didn't get the result I wanted ( probably due to total inexperience ).  I did however have much better success with leaded solder paste and a soldering iron. I saw this in only one video I watched, so thanks to that guy for showing the process.

Where to start?

I started with the two caps right in the middle of the board, there were no components or connectors near them and so it was a good place to get my eye in.  I held the Cap with some tweezers while I slowly move the heating element side to side.  I found I only really needed the air on about 1/3 of the maximum and kept the temp at around 250.  The Caps popped off really easily.

I did find I used too much paste for the first two.  For the next three caps near the floppy connector I used less paste and flux which made a massive difference.

You'll probably notice that I am using the solid electrolyte capacitors from Retro Bench in the photos I did look at pricing buying these myself but it ended up being cheaper to get the kits from them for just doing my two 600's.

Doing the hard bits

There were two areas of the board that I thought were going to be really hard. Between the keyboard connector and the sound jacks and the cluster under the RF modulator.

I decided to tackle the keyboard caps first, I was planning on taking the jacks off but after removing the RF modulator ( and the trouble I had with it ). I decided just to try the Kapton tape.  I removed the top of the keyboard connector first and stuck on the Kapton tape.  I then quickly used the Heat gun to remove both of the Caps.  I then soldered the Cap nearest the white jack first and then the red using a really find solder tip.  In the end it turned out great.

 I am up to the RF modulator and the cluster of caps underneath it basically made this operation really difficult without removing it.  I was going to get rid of it anyhow as I wanted to put HDMI/VGA into this Amiga 600.  I watched a video by Ms Mad Lemon who had a great tip on removing it.  Unsolder the small pins, then unsolder the big pin at the edge of the board, then wedge something underneath and slowly push the other pins through with the iron.

 

I sort of did this.  I removed the small pins solder with my desoldering gun.  I used solder wick and lots of flux to remove as much solder as I could from all of the big pins and worked hard on the big edge pin until it was clean.  Then I used a plastic spudger to help lever the modulator off while using the iron to melt and push through the remaining two pins.

Here we go with the last Caps.  Hopefully it's all working once I get them on.

So I go the new caps on and it works perfectly via RGBI.

Except . . . go read these links . . .

http://www.waveguide.se/?article=amiga-600-video-encoder-upgrade
 
https://www.ikod.se/z221-z222-fix/

https://www.ikod.se/cxa2075m/

 Take home tips

Use tweezers and a hot air rework station to remove the caps.  Not too hot and a medium airflow.

Use small amounts of leaded solder paste and flux to get a good join.
Use Kapton tape to protect plastic bits
Remove the top of the keyboard connector to get some more clearance.
Use solder wick and desoldering guns to remove solder from through hole components
Use plastic spudgers to apply leverage
Remove the RF modulator to get clearance ( chances are you'll never use it again so leave it off ).

** WARNING DO THIS REALLY CAREFULLY ** 

Use solder wick to clean the pads then give it a good clean with isopropyl alcohol.
with a small amount on a cotton bud. Clean up with isopropyl after soldering.

Keep all fluids away from the 221 and 222 metal cans or you will damage them.

If you do damage them . . . well . . . read my blog entry on fixing the Amiga Video.

 

Repair : C64 Black screen with signal : bare board

So I've been looking for a challenging board on Ebay as it's pretty much the only place available for me to find dead C64's.  They are expensive and in general not difficult to fix.  The board I fixed first up was a really dead Gumtree purchase.

Anyhow on with this new board.

1) The Power on flicker

When I first turned the board on I got the "power on" flicker.  This was a really good sign.
The SID on this board is soldered on the board so I'm pretty hopeful it's working at this point.

2)  Dead Test Cart.

Plugging in the Dead test cart I got the black then white flashing screen.  This is a sure sign that one of the RAM chips is dead.

I felt each chip on the board and one of the RAM chips was boiling so I pulled it and put a known good one in.

On turning the machine back on it was still flashing, this was a sure sign that both RAM chips were dead.

I replaced the second one and straight away I got the Basic screen.

3) Jiffy Dos Dead?

The Jiffy DOS screen only stayed up for 5 seconds, then the cursor stopped flashing and then the screen cleared.  I had a spare kernal on hand ( that I had burnt in a previous project ) so I swapped it in and ever since it has been rock solid.

Finale!

Well that was easy, two ram chips, one kernal rom and everything is working, even the SID.

So I'm thinking I am done with C64's . . .

I'm thinking about trying to pickup some dead Amiga 500's as I'm getting a little bored of easy to fix projects.