Fake chips (6532AP)

The 6532AP RAM I/O chip in my Fluke 8080 pod failed and finding a replacement isn't easy as they've been out of production for years. I would borrow one from an Atari 2600 but those aren't the A or AP (2mhz) version required for the pod.

Buying anything from China is risky but usually what you get is used pulls cleaned up and sold as new old stock, I don't mind this if the chip actually works and it is cheap enough. In this case the chip was fake, what they obviously did is take any old chip with the same number of pins / package and print what ever they like on it.

 The chip they showed in the auction looks legit

 However this is what I actually received.

Huge shock it didn't work. I took another gamble and ordered some from utsource in Hong Kong this time, their feedback wasn't quite as bad as the other sellers and they looked to sell pulls rather than fakes. This paid off as the five I received from utsource all worked. 

In future I think I'll bite the bullet and buy locally though, even if they do want £11 a chip!

Amstrad CPC 464 repair

I bought this CPC computer in a job lot a while ago but only just got around to looking at it. The main reason I dug it out was to play with my new toy, a ABI Chipmaster Compact not to be confused with the newer but pretty much the same Professional model. This thing will test TTL logic, the majority of old RAM chips and certain CPUs, very handy.

First thing I had to do was find a suitable power brick in my stash, the CPC464 requires 5v 2amp regulated since there's no regulation on motherboard itself.

All I got was a black screen, after inspecting the motherboard I could see the video output socket had some cracked / dry solder joints. Reflowed and retested, still a black screen but the TV was picking up a signal this time. The Z80 cpu is socketed so I pulled it and put it in the chipmaster.

It failed so I replaced the CPU, now I was getting a blue / green screen with vertical lines. I forgot to photograph this but I suspected the ram as it looked to be running as the lines on screen were changing and moving a little.

The first ram I pulled tested fine but the second one did not.

A fully working CPC 464, and now time to test Rainbow Islands as it's the only game I have for it.

PC Engine Core Grafx PAL RF to RGB

I recently picked up two PC Engine consoles one standard white one and this core grafx. The white one only gives a black screen at the moment so I decided to work on this one instead as it worked. Usually this would be a straight forward case of wiring up a composite cable or rewiring the connector to output RGB, but nothing is ever easy. This Core Grafx had been modded to output PAL RF using an aftermarket pcb and rf box.

What a rats nest.

 Removed the RF box and PCB.

I removed some of the solder mask with a fibreglass pen so I can solder the new connector to the pcb at an angle.

Mega Drive 2 video connector fitted.

Slightly neater than before, I used the through holes in the pcb to feed the wires through.

I should have used a larger connector but since the original was missing I decided to use this one that I had on hand. I also like the idea of being able to use a standard Mega Drive 2 scart lead and not have to make a custom cable.

I installed a THS7314 video amplifier inside the system which I have covered before so won't go over again.

After I tested that it worked as it should I put it back together and then decided to check if C162 should be populated which I should have done before I put it back together, as it turns out it should be. It was so cleanly removed it didn't occur to me that a cap should be there, but a google search told me that C162 is a 470uf 16 capacitor. 

There wasn't room to install it in it's original position so I hot glued it to the pcb where there was space and ran two wires to the two pads.

ZX Spectrum +2 Video Ghosting Fix

Another vintage computer to take a look at, this is a 128K +2 which was made by Amstrad. They made a few mistakes on this model including installing transistors upside down (issue 3 only), mixing the audio with the composite video and a ghosting problem with certain colours again with composite.

You can avoid the ghosting / poor image problem simply by using a RGB scart cable but composite cables are far easier and faster to make. :)

How to separate the audio from the composite video has been covered many times and is covered in this very handy pdf ZX Spectrum 128K video fixes and video cables.pdf so I won't go over it again.

The ghosting fix on the other hand is quite a recent discovery by JoulesperCoulomb on youtube although I found out about it from GadgetUK164's video again on youtube.

 

Basically all you need is a 15uH inductor and two ceramic caps (20pf and 68pf). Connect the inductor to pin 8 of the video encoder join the two caps in parallel and connect one end to the inductor and the other to pin 17, no more ghosting.

Commodore 64 (Breadbin) repair

A rather sorry looking C64 early breadbin model, I've had this for a while and finally decided to have a look at it. First thing I had to do was replace the missing ram at U21 with a socket and 4164. After powering on there was garbage on screen, so still a bad ram or two to find.

This is where my previously made test cartridges came in handy (dead test and diagnostic), first I tried the diagnostic cartridge but the text on screen was too messed up to show anything useful. Next I used the dead test cart and the screen flashed five times, the manual states five flashes is a bad ram @ u10. So I removed u10 and replaced it with a socket and new 4164 ram, this fixed the garbage screen and the familiar blue screen was now visible but it isn't quite sorted yet.

There was a scrolling rainbow colour effect across the whole screen, doing a quick google for 'color' ram shows that the 2114 @ u6 is the colour ram. I removed and replaced this again with a socket and new ram and the colour problem is fixed. I thought this was the end of the repair but after letting the diagnostic cartridge run fully (it was getting stuck at color ram before) it showed that char rom was bad. This rom has the same pinout as a TMS2532, luckily I had one and the GQ-3X was willing to program it.

 

The eagle eyed will notice who ever looked at this previously marked all the working chips with a yellow dot. The character rom didn't have this mark, so who ever it was knew it was bad but obviously didn't have a TMS2532. :)

Donkey Kong (Herbie at the Olympics)

I bought a non working Donkey Kong pcb from Canada to hopefully repair and stick in my vertical cabinet. Turns out it needed a deconversion rather than a repair. This board had been converted to Herbie at the Olympics which I had never heard of until running the rom dumps through rom ident.

The board wasn't running just showing white blocks on the screen, this is because there is meant to be a cpu daughterboard as part of the conversion but this had been removed and just had the cpu put back in the socket. Without changing the rom code back to DK the game will not run.

After erasing and reprogramming all the eproms the game now runs but mostly in black and white due to the three colour proms, once these are replaced it should be 100% deconverted / repaired.

UPDATE: I bought the 3 proms from Mike's Arcade and the board is now fully working.