| Posted By
paulcan2
on 2012-05-14
19:39:01
|  Faulty Plus 4
Hi all,
I used to have a plus in about 1983 as a nipper, just got one to get back into it, and got the same games I owned back then.
My favs were Fire Ant, Ace (64K version) Exorcist, Kickstart and Treasure Island.
I love anything vintage computing currently have lots of old computers and consoles, also loving arcade machines have 12 squeezed into the garage LOL!
I can burn eproms, solder/desoler quite well (the basics you know...)
I can fix arcade boards to a degree so semi handy but...
However I have a plus 4 which was black screen dead, after reading lots about the cpu dying I found a c16 which was killed but had a working cpu, I stole the cpu and yes! Plus 4 all up and running! WOOT
Ok been playing game for a week or two, turned it on tonight and it just says
COMMODORE BASIC 3.5
and thats it, cusor flashing in upper left conner...
leave it on for a while and sometimes BREAK scrolls down the screen
or loads of
PC SR AC XR YR SP
BREAK
BREAK
BREAK
PC SR AC XR YR SP
or sometimes different colour background as I flick the on/off switch.
Any ideas?
RAM?
There are 8 or so 4264's do these go down?
I did once (after flicking on/off for 10 mins) get it to behave and boot up as normal...however goe bad again?
I even swaped the other large chip from the c16
the 8360r2 chip?
Not checked voltages or anything yet I will in the morning though (multimeter, scope etc... are in the garage and it's getting late!)
Any tips to try?
Things to measure?
Please help, or do I just need to buy another?
Thanks Paul
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Posted By
TLC
on 2012-05-15
05:13:40
| Re: Faulty Plus 4
Hi!
I'd try swapping the other socketed chips first (simplest test to start with if you already have some spares). Judging from the symptoms that you're describing, I couldn't name a safe "bet". If it's not the socketed chips, with probably the PLA (251641-02) being the first one, you can probably start suspecting the ram chips, the ram multiplexers (2*74ls257), maybe some other ttl gates. It's all very strange, digital circuits rarely fail like that (they're usually either alive or dead). Ram chips don't usually fail, nor do standard ttl gates (unless there's some shock, say, overvoltage or similar). I'd probably check the supply voltage around the chips using the scope (would be a pity if these symptoms were just caused by badly filtered supply voltage, because of, say, some aging capacitors). In any case, I wish you good luck for the quest!... 
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Posted By
paulcan2
on 2012-05-15
10:21:46
| Re: Faulty Plus 4
Thanks for the reply bud, I did try that just now (week off work) i.e move all socketed chips and still the same.
Ok I have progress I metered the psu and I have perfect +5v but my +9v rail is down to 5.83v
Hmm ok I think psu, anyone uk based have one they wanna sell? Or a c64 one and i'll adapt the connector?
Many thanks,
Paul
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Posted By
MIK
on 2012-05-15
10:55:09
 | Re: Faulty Plus 4
Could always ask on lemon64.com if anyone uses a Plus/4 power pack on a c64? That's if no one can help here with that answer.
I'm sure I have seen plus4's in the past using them or rather the c64 light brown version in the same shape as Plus4 which I believe has been altered, but I would not like to say yes as I don't know for sure.
Yeah normally it's the TED that goes first, tho I have never used the guts out of a C16 before to get a plus/4 working. It's good you have a better idea of what your doing than me any way! Hope you get something sorted soon!
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Posted By
TLC
on 2012-05-15
14:59:48
| Re: Faulty Plus 4
Hmmm, the 9V is not critical, the machine should work even in the complete absence of that circuit (it's only used to power the datassette and User Port cartridges). Anyway, this is 9V AC, maybe that's why you could measure 5.8 volts here (standard multimeters are rarely capable of measuring small AC voltages correctly). As you said, you have perfect 5V, well, it'll still worth checking around the chips when you start inspecting things using the 'scope (so that you can make sure there aren't any spikes and similar interferences on the supply). Needless to say, this is certainly the point where things usually start becoming difficult.
You might probably give a try to crock's system test suite. This comes in an eprom replacing the system roms (you can burn your own chip if you have some means to program an eprom or eeprom yourself; the binary dumps should be available to download somewhere, I just couldn't find them right away). It runs tests for most parts of the computer so it may or may not give you useful hints.
Edit: looked up and found the document ie. Diag264.
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Posted By
raze
on 2012-05-17
04:23:00
 | Re: Faulty Plus 4
PC SR AC XR YR SP appears when you go into the "monitor".
Mine shows:
PC SR AC XR YR SP
; 00FF 00 FF 00 FF F9
Faulty ROM chip?
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Posted By
MIK
on 2012-05-18
19:09:37
| Re: Faulty Plus 4
paulcan2,
I'm not the expert when it comes to faulty things, replacing chips is as far as I can go... and I could be totally wrong with what I'm about to say with your problem!! So please, just view this as an idea to think about looking at just incase...
To cut a long story short I'm been messing with a couple of faulty plus/4's tonight and managed to get one fully up and running.
I'm guessing but I believe your TED is ok. It could be two things being either the CPU 8501r1 or it could be the 3+1 chip being the 317053-01 which is the middle one of the 5 under TED.
You can take the 3+1 chip out and the Plus/4 will boot up looking like a C16 with 64K with GRAPHIC on F1 if removed. Anyways I have 2 faulty 3+1's. One is dead regardless in or out and the other is a proper mess booting up with the normal display but dumping me straight into the MONITOR... It was a naff 3+1 chip doing this.
Edit: Picture of the screen with the bad 3+1 http://i48.tinypic.com/1y38jk.jpg
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Posted By
paulcan2
on 2012-06-09
23:34:05
| Re: Faulty Plus 4
I've put my bad one on the back burner for now as I have found a cheap one with a broken keyboard, so I'm back up and running. WOOO HOOO!
Yes MIK thanks for that ....that is what mine is doing (going into monitor like that)
Sometimes it boots to that and sometimes boots to a blank purple and white screen.
Booo
I did try swapping all chips over and the faulty one still remains the same...?
I'll look at it later or keep it for spares.
Def the mobo/ram at fault as all chips swaps change nothing.
Oh well, as I say it will probably be a spare machine from now on!
I ordered 2 joystick adapters from commodore16.com and only got one?
Complained and still heard nothing, but the scart lead I got from them is still running good.
Feel a bit let down there, had to order a ebay one in the end.
(Still would like another though)
I belong to lots of retro forums (inc arcade ones) and never had any problems but c16.com seem to suck with customer service...well won't be ordering from them again.
Thanks to all of you for this thread you have helped me understand these better than I ever did 20 ish years ago.
Ta
Paul
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Posted By
MIK
on 2012-06-10
01:52:42
| Re: Faulty Plus 4
Hi paulcan2,
Glad to hear you have a working Plus/4 at last! Indeed keep the old one as spares and you did the right thing with the keyboard swap, same thing I would of done.
I don't do many forums to be honest as it takes up too much time so over the years I have slowed down to about 3 now. Have a range of machines and consoles from the ages my self but always return back to the plussy - 1st machine and still fond of it. I'm 15 years old again, I wish! 
This is really difficult... As a community we stick together as you would imagine but what goes on behind the scenes, really sorry to hear this. I hope it's some miss understanding and something can be sorted out.
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Posted By
retroscener
on 2012-06-10
02:08:59
 | Re: Faulty Plus 4
Sorry to hear about your order Paul. I'll try find out what's happened for you.
Unfortunately the main commodore16.com owner goes away for long lengths oftime with other work commitments, and a new family so his attention often gets diverted away from the site, but I'm fairly sure that the problem is through another supplier who's supposed to despatch orders correctly and not from the commodore16 websites end. Will see if this can be resolved 
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Posted By
Chris
on 2012-06-10
02:43:31
| Re: Faulty Plus 4
Thank you for making me aware of this, as I had no idea. I've recieved no emails from you regarding these issues, just gone back through them to check. I did actually see a comment which I think was from you on a unrelated article within the site. The problem with posting comments on articles is that we don't get notifications of that happening. Email is always the best method. Could you forward me your PayPal confirmation email to chris@commodore16.com and I'll resolve this immediately.
Regards,
Chris
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Posted By
paulcan2
on 2012-06-10
06:59:41
| Re: Faulty Plus 4
Thanks Chris/Sixteen Plus for having a look at this for me, I have send you the info just now to chris@commodore16.com (pay pal receipt)
Many thanks,
Paul
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Posted By
paulcan2
on 2012-06-29
14:45:32
| Re: Faulty Plus 4
Thanks Chris refund received, thank you very much for your help and being so professional.
I would use the shop again all day long!
Many thanks,
Paul.
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Posted By
Gorack
on 2015-04-04
20:48:34
| Re: Faulty Plus 4
I had this exact problem. When first turned on the plus 4 would work normally but after a few minutes it would do what paulcan2 describes. I guessed that it was failing when the machine heats up. I wrapped an ice cube up and placed it on each chip until I found that the 6551 UART was the culprit. While the ice cube was on the chip the machine would work perfectly. It was weird, touching the chip you could not feel that it was getting hotter, but it must have been since the ice would stop the problem and the machine work. The solution:- Since i don't really need the UART for 99% of the software I simply cut the 5v trace on the underside of the circuit board to disable the chip.
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Posted By
JamesC
on 2015-04-05
02:14:50
| Re: Faulty Plus 4
Or you could just remove the 6551. The computer will work without it, as long as you don't attempt anything on the user port.
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