| Posted By
TigerPlus4x
on 2023-05-14
01:44:04
|  Troubleshooting Plus4
Hello everyone!! Looking for help, I've found this forum, so here I am, needing help with troubleshooting this PLUS4 machine. To test components, I have a working C-16 (PAL-N).
After checking PSU voltages, I proceeded to turn the PLUS4 on. It showed strange characters on screen. After that, I removed the 8501 and inserted it in the working C-16 (PAL-N). The screen showed something similar, so I supposed the 8501 was dead.
I checked voltage on 8501 socket in the PLUS4, and it was 4.78V, so I tought it was safe to insert the working 8501 there. So I did it. To my surprise, the machine showed the “BASIC V3.5 60671 BYTES FREE”, with READY prompt without any corruption!. So I thought the problem was fixed!
In excitement, I turned it off, brought the datassette and plugged it in.
When turned the PLUS4 on, it showed a dark screen with ascending lines all along, and still like that even now.
I notice the PLA gets hot in the PLUS4, but not when I insert it in the C-16, where it works (at least the startup screen is there without any corruption).
I can burn eproms, I have a TLC 866II and many M27C512 – 12F1. Also a spare 6510 to use as 8501 replacement.
Any suggestions / ideas of how to proceed next? Unfortunately I don’t have an oscilloscope or advanced technical skills, but I can do basic tasks. I'll read you. Many thanks in advance!!!
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Posted By
MIK
on 2023-05-14
06:46:33
 | Re: Troubleshooting Plus4
Normally if you see a black screen the CPU has died, if your unlucky it can also kill the Ted chip when the CPU dies.
If your C16 is working fine it is safe to swap the Ted and CPU to the Plus/4.
In a Plus/4 the Ted sits under the metal shield, the longest chip. To the right of Ted is the CPU. Double check which way the chips go for each machine.
If you get a working machine it's advisable to heat sink the CPU's. You can also heat sink Ted in a C16 as there is plenty of room but for Plus/4 you won't get the case closed with out adding spacers to the case screws to lift the keyboard up. Your best off replacing the heat sink paste for now on the Plus/4 Ted and put the shield back on. Small stick-on heat sinks are fine.
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Posted By
gerliczer
on 2023-05-14
08:38:18
| Re: Troubleshooting Plus4
Find someone who knows what he/she is doing before killing or frying anything else?
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Posted By
TigerPlus4x
on 2023-05-14
12:19:04
| Re: Troubleshooting Plus4
Thanks MIK for you prompt response. I have inserted the +4 TED on the C16 and I get an image out of sync, I think because of different video standard (C-16 is Pal-N uses 8365 TED, and plus 4 8360 TED NTSC).
But I can barely see the startup basic V3.5 line and ready prompt. I typed a SOUND basic command and it worked. The 8501 shows a pattern similar to the one it showed the first time I powered up the machine. So it arrived definitely dead.
The 8501 which I've tested on the plus 4 is working good on the C-16.
*So nothing has been fried*, fortunately. I did everything with caution, consulting videos and documentation before trying. I have read that cold solder joints can also be causing this, so that's something that will be checked.
Considering recapping too. I have burned kernal rom, but the problem persists.
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Posted By
MIK
on 2023-05-14
16:59:07
| Re: Troubleshooting Plus4
NTSC hardware is out of my league as I'm from European PAL land and is the only hardware I have ever messed with.
If your NTSC USA, I believe Brazil had PAL C16's, I'm not sure if the ROMs are compatible. Check the base of the case, it may have a serial sticker stating where the machine may of been made. If it has been imported it may say Made in UK or Germany.
If it's second hand you can't be 100% sure if the mother board belongs to the case though...
ebay may help with finding the correct spares.
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Posted By
JamesC
on 2023-05-17
14:01:39
| Re: Troubleshooting Plus4
The 8365 is only found in the Drean Commodore 16, which was assembled in Argentina and designed specifically for Argentina's PAL-N video systems.
The Plus/4 was never offered in Argentina. Your Plus/4 is either a straight NTSC machine (US/Canada) or straight PAL machine (Europe); please look at the silver sticker on the bottom of the Plus/4, and let us know where it was assembled.
EDIT TO ADD: Please also look at the bottom of the Plus/4's power supply, and let us know the part number you find there. This will tell us if you have a 60Hz power supply (US/Canada) or a 50Hz power supply (Europe), which affects the video output and whether the chips may overheat.
Once we know what you are working with, then we can offer suitable advice. In the meantime, we would only be guessing. 
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Posted By
MCes
on 2023-05-18
03:02:35
 | Re: Troubleshooting Plus4
4.78V appear to be a little low:
(with +4 ON) try to measure the "5V" line before the switch, try also the same switching it off.
In OFF position arrange the multimeter for current measurement and use it on switch pins for closing the 5V line (beware to not make contact with 9V AC lines!) if it is more than 1A a problem can be.
You can also swap PLAs (C16->PLUS4) and repeat the current measurement
Link to a current measurement inside a +4
https://www.amibay.com/threads/plus4-c-mos-romset-replacement-less-heat-inside-it.111677/
Link to my cpu replacement solution (high compatibility) (high compatibility)
https://www.amibay.com/threads/8501-7501-cpu-replacement-for-c16-cpu4c16-and-plus4-cpu4plus4.115399/
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