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Donkey Kong TKG-04-CPU board repair


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Hi,

 

I have a TKG3-04-cpu board I am trying to get up and running. This is a 4-board stack. Similar if not identical to the radarscope cpu board with readily available cpu board schematics pages 6 and 7. I have confirmed that the video and clk boards work with my other cpu board.

 

What is the problem?

Z80 boots to garbled screen then blank screen waiting and waiting and waiting ...

 

What I've done so far?

 

1. Power - good

 

2. Z80 CPU

 

- clock signal pulsing away

- reset low then high - watchdog sleeping

- address and data lines pulsing away

 

- NMI active low - high

- IORQ active low - high

both should be pulsing

- BUSAK active low - high

- HALT active low - high

- INT active low - high

- MEMRQ active low - pulsing

- RD active low - pulsing

- WR active low - pulsing low

 

- WAIT active low - pulsing low

- BUSRQ active low - pulsing

- M1 - active low - pulsing

- REFRSH active low - pulsing

 

 

3. 4-channel DMA Controller 8257

clock signal pulsing away

reset high then low - watchdog sleeping

address and data lines pulsing nicely

 

Note: Channels 3 and 4 are inactive on this setup.

 

IOR - active low - pulsing

IOW - active low - pulsing low

MEMR - active low - high

MEMW - active low - high

 

READY - active high - pulsing low

 

HLDA - active high - low

HRQ - active high - low

these should all be pulsing

 

ADSTB - active high - low

AEN - active high - low

 

 

CS - active low - pulsing high

DACK0, DACK1 - active low - both high

DRQ0, DRQ1 - active high - both low

these should all be pulsing

 

MARK - active high - low

TC - active high - low

 

 

 

From google

Following is the sequence of operations performed by a DMA −

 

Initially, when any device has to send data between the device and the memory, the device has to send DMA request (DRQ) to DMA controller.

 

The DMA controller sends Hold request (HRQ) to the CPU and waits for the CPU to assert the HLDA.

 

Then the microprocessor tri-states all the data bus, address bus, and control bus. The CPU leaves the control over bus and acknowledges the HOLD request through HLDA signal.

 

Now the CPU is in HOLD state and the DMA controller has to manage the operations over buses between the CPU, memory, and I/O devices.

 

4. Now I have to figure out why no CPU and 8257 aren't talking.

 

Will do some reading now.

Edited by hvc01
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Working my way down through video circuit and 4G pin 4 NMION is stuck low (active high so OFF) and NMI pin 5 stuck high (active low so OFF). If pin 4 contacts clock pin number 3 - sprites appear on screen and can see jumpman and fireballs etc.

 

so 3D, 4E and 4F seem to be working for this circuit.

 

4G isn't working probably due to NMION not pulsing.

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went back over other side to 3M. 74LS259 (NB equivalent chip on tkg4-14 cpu board would be 5H)

 

pin9 (NMION), 10 (BLKTRS0), 12 (CREF0) all stuck low.

 

when compared with working board 3M pin9 and 10 should be pulsing.

 

pin9 drives nmi requests for z80 - ie. the assembly code within the nmi interrupt section includes all the important code before the screen refresh

pin10 drives the drq requests for the 8257 DMA controller - ie. data lookup and transfer etc

 

I have replaced this chip already but unsure if I put the same one back in. This would make sense.

 

I will pull another one from a donor board.

Edited by hvc01
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In hindsight i should have stopped once I tested the eproms. Only 1 chip enable pulsing. Others stuck high. I did replace the eprom controller ic because stuck there also. Must be the inputs which are addresa lines and refresh. They prob look on logicprobe. Prob look shit on oscilloscope.

 

The dma and z80 and another 74sl259 all tested and working.

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