Repair – JunoMan’s Arcade Blog

Toaplan Truxton TP-013B repair

Another quick repair log. I forgot to take photo’s this time.

The board tried to boot but just had a line of yellow text saying ‘XVVSIDXXVVVVV’. That usually means there’s an issue with the text layer. Using the ‘wet finger on the pins’ of the 4 SRM20256 SRAM chips at F14 to F18 showed some changes to the text when I touched the data pins on F14. Desoldering it and testing on my Wellon VP280 showed it as bad. (no continuity on the data lines). Replaced it with a Sony CXK58256P aka 62256 and got a working screen.

Now it showed ROM OK, RAM OK and SOUND CPU BAD. This most likely meant that the 6116 at F1 was bad, (although it can mean otherwise). Desoldering and testing the chip showed the A0 pin to be faulty. Replaced it with a Hitachi 6116, fired up the board and was presented with the same error message.

After looking at the Rally Bike schematics which is basically the same board, showed that the 68000 can access the sound z80’s work ram. This is done by using the BUSREQ pin to tell the z80 to get off the bus. There is quite a bit of circuitry to handle this.

Since the 6116 showed a fault with the A0 line, the z80’s A0 line could be bad too. I desoldered the z80, put in a socket and tried another z80. This new z80 was a pull and was in fact bad. The board didn’t even boot, and without the z80 in the socket it won’t boot either. I tried another working z80 and the game booted with the same fault.

Now it was time to look at the support chips that handle the interaction between the z80 and 68000.

The 68000 uses 3 74LS245’s to access the address and data bus, and a 74LS244 to set the control lines when the z80 gives up the bus.

Looking at the chips, I noticed the 74LS244 is a Fujitsu chip and if you read many other repair logs you’ll see a pattern of Fujitsu chips rapidly and randomly dying. A good candidate.

Desoldering and testing the 74LS244 showed, you guessed it, as faulty. Replacing it with a known brand pull (rather than Goldstar chips from bootlegs!) and the board fired up 100%.

Another classic saved.

PS You have to be careful desoldering chips on these board as they used a ground and power plane. This sucks out all the heat making it extremely hard even with a desoldering station to extract the chips without damaging the pcb.

Repair of a mystery Commodore 1541 clone PC-606 drive

I noticed a strange 1541 clone for sale on TradeMe over Xmas which according to the seller started smoking when he powered it up to test. I put a bid on it and it went for a song.

It duely arrived and I opened it up. There are no identifying markings on this drive other than PC-606. Googling that just shows the Trademe auction. The floppy drive itself is a Gold King GYE55A also give no results when googled.

First thing I noticed was a discoloured tantalum cap on the main pcb. No surprise there as they tend to short and since the PSU is a linear type it feeds more amps into the circuit until something fries.

Toasty C7 presumably a 10uf 25v – Note the floating TTL chip and “we don’t have any 4 way resistor packs so a 8 will do” bodge.

Googling typical original 1541 faults showed that a 10uf in the 12v line usually shorts. I checked with a digital meter on continuity test and it indeed was shorted. After replacing it with a electrolytic and powering up the drive with the floppy cable disconnected got the board booting, with the drive light coming on red for a few seconds as expected.

I connected the floppy drive to the main pcb and powered it up, expecting the repair to be done. Low and behold more magic smoke appeared. This time it was a tantalum cap on the floppy drive itself.

I removed the melting cap and checked the 12 volt rail which still showed as shorted. Checked the rest of the tantalum caps on the pcb with the meter and found another 4.7uf cap was shorted. Removing that cap resulted in no more shorts. There were no shorts on the 5v rail fortunately. Replaced both caps with electrolytics I had to hand, and after re-assembling, the drive power up without loosing any magic smoke.

Strangely the power LED stopped working. After checking that the LED was getting power I noticed the green wire wasn’t even soldered properly as it wasn’t stripped properly. Must have only just been connected since it was made in 1985. Resoldered the wire and the power LED worked fine.

Put it all back together and connected it to my C64. Tried a couple of disks and its all working fine now.

It even comes up with the normal 1541 version on boot. I’ll dump the eprom to see if its different from a real CBM drive.

[Edit] I dumped the eprom. Its 1541-325301-01 joined with 1541-901229-05.

IREM X-Multiply repair log

Another great horizontal shooter from IREM.

Very low volume was the first issue. Checked the volume pot as it had been changed. Was the correct value. Replaced the 1000uf capacitor that was visibly bulging and the sound came back very loud!

When it is first powered up all the ROMs and RAM 7 show as bad, but powering the game off and on again reports RAM OK ROM OK.

Left for a few minutes it doesn’t again.

Having already replaced the capacitor which was bulging, the rest of the capacitors were suspect.

M72 games have a reset chip at ic7, with two timing capacitors. Shorting out both when the board was powered off produced the same error message every time. Replaced both capacitors at C8 and C10 got the board reliably booting.