Got a few boards today.
One of them is an original Capcom 1943 board.
Game had no sound at all.
After a quick look over the problem became apparent.
The EPROM for the sound was missing its GND leg. I replaced this with a 27c512 (data doubled up) for now as I seem to be out of 27c256 EPROM’s.
Game is fully working now.
Ive been wanting to get a RAM upgrade for my VIC20 ever since I found Robotic Liberation demo wouldn’t load from SD2IEC unless it was expanded. As eBay prices have gone stupid I opted for the homebrew piggyback method.
This method involves soldering a couple of 6264 RAM chips onto the Kernel and the BASIC ROM’s and lifting a few legs to run some wires elsewhere.
The guide I followed can be found here so I wont bother rewriting it.
Its pretty easy to follow but found it best to read through it a few times before starting.
I had already replaced the Kernel ROM in my VIC for a JiffyDOS one using one of my adapters so some of the work was already done for me regarding the pinout differences but as the guide says, best to check the operation after each RAM is fitted to confirm its working.
Anyway, here are a few pictures
You can see my custom board in the lower right hand corner of the PCB
And following the upgrade
Completed mod
And finally, Robotic Liberation
Its pretty easy to do and fairly quick once you understand the instructions.
As Ive been doing some repairs on divIDE’s and I didn’t already own one, I picked up a nice cheap 128 on eBay the other day, sold as powering up but wont load games.
At first I suspected it was just a dodgy tape drive and as I would be using the divIDE to load stuff it didn’t bother me.
So, it arrived and I powered it up and it worked OK. I loaded up my test game and it loaded fine but then crashed. I tried it again a few more times but kept crashing at random points. Time for another going over with the 9010 I thought, only when I fitted it, it no longer crashed. I replaced the Z80 for a brand new one and its been fine.
Nice and easy
The divIDE, as the name suggests, allows IDE devices to be used on a Spectrum computer.
Got 2 of these to fix recently.
Both of them would not allow the Spectrum(s) to boot up. When I tried, I got to the boot up screen but it was locked up.
As all the chips are socketed I checked them first.
I started with the green PCB.
I found was a blank EEPROM which I reprogrammed with the FATWare bios.
On fixing all the initial faults neither board would work still.
To try and make some short work of fault finding I removed the Z80 processor and fitted the Fluke 9010.
With this fitted I basically ran a loop test on each address and data line and the status lines.
Found that data line 3 was not making it back from the EEPROM to the processor. Following the traces back I found the pin at the edge connector had come away from the solder pad.
I re soldered and tested. The divIDE was fully working again.
On to the red PCB
All the GAL chips could not be read out at all and flagged up errors on pins. The RAM also failed when I tested it.
Talking to Questor on the RCM forums, he tells me that dead GAL chips are a sign of the device being removed while the unit is still powered up.
After some quick probing around I found a transistor had blown. I also took a gamble and tested the other 2, both of which were dead.
After replacing all of these, this unit is now working too.
A nice device but would benefit from a case I think.
PC18 from Jamma+ forum dropped me 2 UMK3 boards around a while back in the hope we could get one of them working.
Both had sound issues.
The first board failed its self test flagging the ROM U2 as bad, when one fails none of the others are checked and the game boots.
The second board just had a feedback sound playing all the time and no game sounds were there even though all self tests pass.
I check the ROM’s out first and they were all fine
Checked the voltages on both boards and they were all fine.
Probing around at the sound ROM’s on the first board I could see that none of the chip select lines were ever being activated. I traced this back to the protected GAL22V10 chip, fortunately I had another GAL from the second board but got the very same fault. Refusing to believe that both chips were bad and in the same way I started looking elsewhere.
The ADSP-2105 chip is the sound processor on this board and could see that all the address and data lines were completely dead.
At this point I wrote the board off and focused my attention on getting the second board running.
I know that if the -5v is missing then the you will get the very noise that I was getting with this one. Only trouble is all the voltage levels were fine to all points I could trace.
These boards have A LOT of small surface mounted capacitors and resistors which makes tracing things out a huge task and as there are no schematics available I was getting a bit frustrated.
Out of frustration I decided to probe the sound processor on the board and found that on start up all the address and data lines are in fact tri-stated just like the first one so it got me thinking that the other board was maybe OK.
Looking around on the underside of the board I found this
This actual mark was tiny until I starting prodding at it and missed it on my initial inspection but there was no continuity between the 2 ends of it so it was cut all the way through. Even better news was it did go to that GAL chip so probably would affect the sound circuit.
I patched the trace with some kynar
Fired the game up and was greeted with a 1 tone sound which actually means the sound hardware is OK, previously I had 2 tones which means there is a fault.
Due to the reason mentioned above I’m not going to try fixing the other board up but I have confirmed that all the processors and stuff are working so there are spares should he need them.