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Vendetta repair log #2

Jan 022015

Got this original Konami Vendetta PCB from a batch of faulty boards I recently bought:

Board was really brand new as it was come out from the factory but once powered on I was greeted by a flashing white screen sign that the watchdog circuit was active and the board kept to resetting:

Usually the watchdog is on because there is some troubles in the main code execution.So I started with my multimeter the check the main CPU (a custom marked ‘053248’) area and found an high resistance between ‘D1’ (DATA LINE 1) of the CPU and the program ROM:

Obviously, for the proper CPU operation, all its address and data line must be daisy chained with the main code ROM as confirmed also by schematics:

So I used a provisional patch wire and board booted fine:

But external appearance matters too.So, following the path of this data line, I found the point where the track was interrupted (picture on the right was taken with USB microscope) and I patched it with some AWG30 wire:

Job done.

Oric repair log

Dec 312014

today I got a couple of Oric computers.
Ive been after one of these for some time now but prices have shot up of the last 12 months.
I couldn’t resist buying these two, both of them which required repair, as the price was right.

First is red/black one.
I first started by removing the ULA and powering up to check voltages. I do this with Spectrum’s too as these early voltage regulators have a habit of going wrong with disastrous consequences.
With everything looking OK I refitted the ULA and power up. I was greeted with this screen.

Ive read enough about the Oric over the years to know that the ULA is very hardy and the RAM is very poor. Ive also read that a fried ULA will usually result in nothing on screen at all.
I opted to desolder the RAM first.
There are 8 x 4164 RAM chips and on testing two of them failed.
I socketed and replaced the faulty RAM and I now have this

The random writing is my doing as the keyboard is flat on the bench when testing.
Happy with this. I think the second unit has the same fault too.

SEGA Mega-Tech PALs added

PAL Updates Comments Off

Dec 302014

Zebow2002 has loaned me a Mega-Tech motherboard and a bunch of games. Here are dumps of the 3 PAL’s found on the board.
At this point they are untested but I could really do with them being tried out as they may be the cause of the fault.

Thanks to Zebow2002

Fluke 68000 POD repair log

Equipment Repair Logs, Repair Logs Comments Off

Dec 292014

Whilst doing some testing for Guddler over on the UK-VAC forum I thought it would be a good time to look into why I sometimes get a POD timeout error.
Normally when I get this error pushing down on the black cable that connects it to the 9010 fixes it.
Here is the reason why

One of the crimps had worked its way loose.

I carefully bent the small bard out a little and refitted. Now the POD seems to be rock solid.

Hard Drivin GAL dumps added

PAL Updates Comments Off

Dec 292014

muddymusic dumped the Hard Drvin GAL16V8’s from his board set. They were unlocked so are assumed working but have not been tested.
Thanks to muddymusic

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