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FROG repair – bootleg Frogger


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Frog, a bootleg of Frogger on hardware marked KPOK-01A

Problem reported: unknown state – found in a box. Missing some parts.

 

IMG_20190916_182101.jpgIMG_20190916_182044.jpg

 

Faulty parts replaced:

 

18.432 crystal oscillator

IC86 – 2114 SRAM

IC4 – 74LS367

 

The sound board was missing three EPROMS in locations 32,33,34 missing as was the AY-3-8910 sound chip at location 35 and 8255 I/O chip at location 40. All audio amplification components where missing.

 

First I cleaned the boards with compressed air and examined for any signs of physical damage on the PCB traces and components.

Sega / Gremlin published a Frogger service guide back in the day – it contains schematic drawings and troubleshooting, although some minor differences (and mistakes) the majority of component and interlinks match between this bootleg PCB and the original board set part.

 

I measured across the DC input to check for dead shorts - I removed and replaced the two 220uf capacitors. I made a harness and hooked up my linear bench PSU and applied +5VDC, board powers up and consumes steady 3 Amps. I then set +5.2V delivery to offset voltage drop on furthest chip

Using a scope, I can’t locate pulses anywhere on the board I check around the crystal oscillator and it’s flat lining.

 

dud crystal.jpg

 

The main CPU crystal oscillator is 18.432 Mhz so assuming the crystal is dead I fit a brand new crystal however the board remains without any pulse and is stone cold dead. I double and triple check everything power related. I look on the sound board which has it’s own 4Mhz oscillator and CPU and there is a clock pulse present but the CPU is held in RESET.

 

Back on the game logic board I start looking at the oscillator driver buffer circuit, it’s an 74LS368 at location 73 still no sign of pulses, only 5v at the supply pin – nothing else. I decide to isolate the clock circuit from everything else by removing the divider LS107 at location 72. Still no pulses.

Measure the capacitors and resistors, they are OK. I vector test the LS368 on my TTL chip checker and it shows OK. I put in a new LS368 but still nothing. All that remains now is the crystal oscillator again – I don’t have another 18.432 Mhz – but I do have 19.660 Mhz, so I fit that and start seeing clock activity.

 

timing circuit.png

 

I order the correct crystal and when it shows up I now have proper 6Mhz on pin 3 and inverted 6Mhz on pin 13. Hmm, two dud crystal oscillators – that sucks. I make a note to build a crystal tester at some point in the future.

 

working crystal.jpg

 

I connect outputs to RGB monitor. The game code is running. Attract mode works, coin up and player start the main game code appears to be running but the graphics are not right. The objects appear fragmented and broken. The tile graphics are in the wrong positions with corruption and random placement of other text on the screen. I don’t see the character frog and joystick inputs don’t seem to influence anything in game play mode.

 

frog1.jpg

 

Using scope I start looking at the data and address lines of all RAM chips, the video RAM circuit – pin 13 on 2114 SRAM location 86 looks different to the others in attract mode. In game mode the pin data changes slightly but it’s measuring 1 Volt lower than other data lines I suspect a faulty chip. I try piggyback using a known good 2114 SRAM chip and see some improvement. I remove the SRAM chip off the board and replace it. There is some improvement in the graphics but it’s still not right - there is fragmentation on tiles and object character scrolling (vehicles, logs, turtles etc) is not working properly.

 

frog2.jpg

 

The Sega service manual has some troubleshooting steps “Off positioning of character or when character such as frogs do not appear” seemed match the issue I was having. It suggests IC 37 and IC 49 both LS161 counters between object RAM and TTL RAM – these checked OK and IC 47 and IC 48 both LS86 driving the address pins checked OK, or so I thought.

 

HCMPI circuit.png

I was poking around measuring the object SRAM pins and accidentally shorted between RW and I/O4 Pins 10 and 11 on 2114 IC50. In doing this I noticed that the object graphics looked improved, however the main character frog was still missing, and the objects where still not scrolling correctly. This led me to think the problem might be with the LS367 object RAM buffers IC39,38,52 but they all checked OK.

 

IC50 SRAM.jpg

 

I then went looking on the object RAM control line from IC15 LS138, the inputs and outputs here looked OK. I check the three other selectors IC16, IC17, IC18 all LS138 and they looked OK. In retrospect here was an oversight on my part, some of the address lines measured 3.9V peak to peak but since it’s driven from three LS367 that fans out to many other parts of the circuit which seemed to be working I assumed probably OK with that amount of Voltage drop. Well I was ultimately wrong but I’ll tell you how I got around to knowing that in a roundabout way.

 

At this point I started looking at the 8-bit address latch LS259 @loc 42 and found here is where the Sega schematic and this bootleg board differ in design. I went through and mapped out the differences and was able to account for all expected behaviour except the HCMA line which was being held high. I power cycled the board a few times and HCMA was kept held high in all control modes, the Sega schematic does not represent HCMA control line as a normal state high.

 

z80 74ls259.jpg

 

HCMA line output from LS259 fans out to a number of places including the object RAM circuit - LS08 @ IC65 resolves into HCMP1 that goes through LS377 and ends at the second inputs of LS86 @IC47 and IC48 object to TTL RAM address bus. I had previously measured these inputs and assumed high state was normal. I figured the LS259 was at fault and so it was replaced, now the game started up in attract mode working normally. However success was short lived the object graphics began glitching again within a few minutes it was as bad as before. Damn.

 

74LS259.jpg

 

Since I spent some time tracking all the outputs from LS259 I now started paying closer attention to the inputs. I assumed everything looks OK except the buffered CPU address lines from three LS367 with average peak to peak signals around 3.9V

 

A quote from the Sega troubleshooting guide page 11 section 3 “Buffer for address bus of IC3, 4, 14 especially too much fault of temperature” the three LS367 are the CPU address line buffers and on this board never feel slightly warm no matter how long the board has been powered up. Must have been a known failure mode back in the day and these are Fujitsu parts I guess at least 35 years old now.

 

I didn’t have any spare LS367 chips but did have plenty of HC367 which are logic compatible only in CMOS. There are design rules for intermix of logic types it’s quite an interesting topic, however I went ahead and replaced IC4 with a new HC367 and the Frogger board began working properly in all modes. I played a few games and left the board running over night (with the RGB monitor off) the following day it was still working OK.

 

 

 

So I reckon that’s fixed the main game for now, the sound board however is missing audio parts and needs attention next on my things to do list.

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Thanks Arcade King!

 

I had a look at MadMikeAU post for the "Frog to Frogger" conversion since the board I have is a bootleg "Frog" - it's a good candidate for an upgrade :)

 

I downloaded the .BIN files MadMikeAU modified, the instructions he wrote up are very good and the change is easy enough, for "Frogger" title and Konami

 

My EPROM programer does not play well with older type EPROMS, it's a Wellon VP-280 that struggles with anything smaller than 27C512. Since this modification requires two 27C32 EPROMS for the conversion.

 

I had some 28C64 EEPROM that my programmer was perfectly happy with they are 28 pin compatible with 27C64. I figured this was my best option so I removed the three 24 pin sockets for the main CPU code IC6, IC7, IC8 and fitted 28 pin sockets with some modification so it did not damage the traces underneath unused pins. The reason I did this I don't like pin overhang on sockets, it looks a bit untidy I think..

 

I doubled the .BIN files to suit 28C64 and programmed them for IC6 and IC8 then using trace wire under the chip connected pins 26,27,28,1,2 - that pulls up the unused address pin and links voltage to the supply pin. Powered the board up and it works looking like a legit Frogger now.

IMG_20191108_101628.jpg

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Thanks Arcade King!

 

I had a look at MadMikeAU post for the "Frog to Frogger" conversion since the board I have is a bootleg "Frog" - it's a good candidate for an upgrade :)

 

I downloaded the .BIN files MadMikeAU modified, the instructions he wrote up are very good and the change is easy enough, for "Frogger" title and Konami

 

My EPROM programer does not play well with older type EPROMS, it's a Wellon VP-280 that struggles with anything smaller than 27C512. Since this modification requires two 27C32 EPROMS for the conversion.

 

I had some 28C64 EEPROM that my programmer was perfectly happy with they are 28 pin compatible with 27C64. I figured this was my best option so I removed the three 24 pin sockets for the main CPU code IC6, IC7, IC8 and fitted 28 pin sockets with some modification so it did not damage the traces underneath unused pins. The reason I did this I don't like pin overhang on sockets, it looks a bit untidy I think..

 

I doubled the .BIN files to suit 28C64 and programmed them for IC6 and IC8 then using trace wire under the chip connected pins 26,27,28,1,2 - that pulls up the unused address pin and links voltage to the supply pin. Powered the board up and it works looking like a legit Frogger now.

https://www.aussiearcade.com/attachment.php?attachmentid=155951

 

woohoo!

anther win for the new search engine

Thanks for sharing!

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Around the same time, I figured the CMOS I used for the repair in IC4 looked like an option to swap IC14 and IC3 for CMOS HC367 for the address line buffers as well.

I was curious to see what would happen and even though the LS chips in place appeared to be working perfectly happy.

Removing the original Fujitsu chips, the leg pins quite literally just fell off they had corroded so much, it was amazing they worked at all. It seems Fujitsu pins 4,5,11,12 with the center section cut out at the body of the package.

 

The board works as expected with CMOS address buffers, looking at the signals on scope the characteristic are quite a bit different, voltage undershoot particularly with peak to peak measurements reaching over 6Volts at times. This is CMOS territory, Soon find out if it kills some defenseless LS chips else where in the set.

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