Posted By
Hendriks
on 2019-08-16
06:03:35
|  Plus/4 black screen : TED, CPU, PLA, and ROMs are good
I have recently bought a plus/4 that outputs only a black screen. I have a working Plus/4 with a brand new modern power supply that works, so I know the power and monitor connection is fine.
The red power LED lights up. I swapped the TED, the CPU, the PLA, and the ROMs with my working plus/4, and they're all fine and working normally in my good machine.
I checked the board as best as I can, I'm no electronics expert, but I recently bought a multi-meter. There do not seem to be any resistors or capacitors broken or shorted.
I noticed the RAM chips getting too hot too touch very quickly. Does that mean that I have to buy a soldering iron and replace the RAM, or is there anything I can do before that?
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Posted By
gerliczer
on 2019-08-16
07:56:18
| Re: Plus/4 black screen : TED, CPU, PLA, and ROMs are good
Recently, someone had a faulty ACIA (U3, 6551/8551) that brought the whole machine to its knees. It may worth a try pulling it out and do a test run.
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Posted By
Hendriks
on 2019-08-16
08:23:38
| Re: Plus/4 black screen : TED, CPU, PLA, and ROMs are good
Thanks for the suggestion. Is there any way to see if it's the problem without pulling it out? It's not socketed and I would need to get a soldering iron, and I have never done that before.
Is there a way to measure with a multi-meter and see if it's working normally?
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Posted By
gerliczer
on 2019-08-16
11:38:42
| Re: Plus/4 black screen : TED, CPU, PLA, and ROMs are good
See the opening post of the following topic: http://plus4world.powweb.com/forum/37911.
I think, its not possible to do anything more without oscilloscope and soldering iron.
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Posted By
candle
on 2019-08-16
20:41:58
| Re: Plus/4 black screen : TED, CPU, PLA, and ROMs are good
i strongly suggest not to
if you're "not an expert" and just recently "bought a multi-metter" just don't buy solder iron just to damage the board
from what you've wrote, fair chances are that ram chips (all or some) need to be replaced, and there is good chance of damaging the board by doing so by unexperienced person
if you would like to learn how to do that - get a scrap c64 to practice - they are plenty  (just kidding, but then otoh, they are...) or just get some pc isa card (multiio for example - they should cost next to nothing) and practice desoldering
it's nothing you probably can't do, but it takes time and practice to do it good
spare ram chips aren't that expensive, and it is simplier to cut their legs off and then desolder one after another than whole chip at time, but feel free to take your own approach
just remember to put a socket for every chip you replace
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Posted By
Hendriks
on 2019-08-17
05:26:49
| Re: Plus/4 black screen : TED, CPU, PLA, and ROMs are good
Thanks for the good feedback! After a lot of internet research, I bought a good soldering iron (Hakko FX888D) and a desoldering station with a vacuum pump (AOYUE Int474A++).
What you describe is exactly how I will do it. I ordered new ram chips, sockets, etc. I will practice on some old PCBs I have lying around first. I watched a lot of youtube videos and I've heard the warnings on what can go wrong.
I really want to get good at this as I have plans to get more plus/4s and C16s, and I want to build my own mechanical keyboards as well (for modern PCs).
I only paid 30€ for this plus/4, but it looks like new and I want to get it going again, not destroy it.
I will post again when I'm done. It will probably be a couple of weeks.
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Posted By
MMS
on 2019-08-17
13:38:39
 | Re: Plus/4 black screen : TED, CPU, PLA, and ROMs are good
OFF
Frankly speaking, soldering became complicated since they introduced lead-free soldering and you cannot get lead for soldering. You need flux and so.
I do not lie: lead is poisinous to your body, but only if you do not handle with care. If you eat after that with unwashed hand, or eat/dring during work. Otherwise...
There were several side effects of the lead-free soldering too, namely the strong acids and their fumes you breath in (and you really cannot prevent flux if you want to go lead-free). In fact, after introducing lead-free soldering, several ppl hospitalized due to poisonuous gases they inhaled (was not the case with lead)
I am also not a soldering master, but receintly I tried to do some for hobby, and it was a very bad experience. I remember how much easier it was when I made my Covox card soldered with lead.
So I will surely buy some old lead soldering mat to make my stuff. Otherwirse I just overheat these old PCBs (anyhow soldered with lead).
If you are for lead-free, I highly suggest to buy good quality soldering mat (they are pretty expensive) with flux loaded inside the wire, with low melting point.
Typically the ones containing silver get close to the 210°C meltig point.
(Stannol, Weller are really good, but there are some good ones too. Do not choose high Cu contetnt version, you will bot able to manage those ones have more than 1% copper content)
A random quote from someone on the internet:
"As a newbie solderer I found the temp controlled iron was a big help with lead free solder.
I had a big reel of lead solder handed down from my wifes dad. No idea how old it was but its lasted me a long time and gave great results even with a cheap iron.
The difference I found is that the lead solder is more forgiving.
The lead free solder needs extra flux and everything immaculately clean.
I find rubbing the solder pads with the pcb rubbers/cleaners, even if they look clean, essential."
ON
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Posted By
Hendriks
on 2019-08-26
05:12:35
| Re: Plus/4 black screen : TED, CPU, PLA, and ROMs are good
An update to this topic as promised: I desoldered the RAM chips and put them in sockets. It turns out three of them were broken. I got new ones on eBay (new old stock), and now the machine is running again. Desoldering and soldering was a bit tricky as first, but I went slow, carefully, and methodical. It was actually a lot of fun, and I'm sure I'll be doing it again.
Thanks for all the help and suggestions.
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