Posted By
repetto74
on 2017-10-30
16:19:46
|  Commodore 16 and 'Device Not present' error :-(
Hi Guys,
I have picked a Commodore 16 a few days ago from a local sale. The machine looks OK and will boot up normally. Problem is when I want to use my SD2IEC connected to the serial port, I'll just get a 'Device Not Present' error message while trying to load the SD2IEC browser. I have tried also with a 1571 Disk Drive but same message  . What this can be? Faulty chip?
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Posted By
siz
on 2017-10-30
17:55:24
| Re: Commodore 16 and 'Device Not present' error :-(
The SD2IEC is often set up to act as device #10. Try DIRECTORY U10 command to check if that's the case.
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Posted By
repetto74
on 2017-10-31
05:00:16
| Re: Commodore 16 and 'Device Not present' error :-(
Hi Siz,
With the 1571 Disk Drive connected I'll get the same Device error message when typing the command LOAD "FB16",8. I will give this a try later today and revert. Thanks!
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Posted By
JamesC
on 2017-10-31
12:29:38
| Re: Commodore 16 and 'Device Not present' error :-(
The 1571 has dipswitches on the back -- be sure the 1571 is set to respond as device 8 (both dipswitches in the "up" position).
Also, if you have any 1551 drives attached (even if not turned on), they will take priority over a serial device of the same number. For example, a 1551 as U8 means that a 1571 cannot also be U8. This is different than the C64/128, where different drives can appear with a flip of their power switch.
There is no single chip that controls activity on the serial bus. Can you verify that the SD2IEC and 1571 work on a 64 or 128, using the same cable between the device and your 64 or 128?
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Posted By
repetto74
on 2017-10-31
13:58:18
| Re: Commodore 16 and 'Device Not present' error :-(
Hi JamesC,
The 1571 is set with switches up to the 8 device number an working perfect with my C64. No other drives attached at the same time and the SD2IEC is working ok with the C64 as drive 8.
Attached a picture upon testing.
Are you sure about the bus activity? According to the C16 schematic from the service manual the serial port is controlled by the 8501 CPU. Now and do not know how a potential damaged 8501 can just make the serial bus to stop working and the rest looks ok.
https://ibb.co/gPCQsb
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Posted By
repetto74
on 2017-10-31
14:03:20
| Re: Commodore 16 and 'Device Not present' error :-(
Here is the schematic with the serial bus details. I think this is from a Plus4 both the design was equivalent with the C16.
https://ibb.co/bvHGXb
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Posted By
siz
on 2017-10-31
14:58:00
| Re: Commodore 16 and 'Device Not present' error :-(
If your drives work with the C64 that means that you really have a hardware problem. First thing to try is to replace the 7501/8501 CPU as that's the one that controls the serial bus. In most cases that's the culprit.
About the TCBM (1551) preference over serial: it's done by software in the KERNAL: if you try to access device #8 or #9 it first checks if a 1551 drive is present with that number. If that's not detected it will send the usual device number talk/listen commands to the serial bus.
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Posted By
repetto74
on 2017-10-31
15:19:25
| Re: Commodore 16 and 'Device Not present' error :-(
Hi SIZ,
Replacing the 8501 will be very difficult. This chip is impossible to find over the web and the only 2 or 3 I saw are just overpriced to 2x the value of a loose C16.
If you know where to find a working 8501 at a decent price please tell me  otherwise I have to consider the machine Out Of Oder unfortunately
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Posted By
repetto74
on 2017-10-31
15:26:38
| Re: Commodore 16 and 'Device Not present' error :-(
Now if I look the schematic I do see that each line of the serial has a diode in-between with the CPU. I may need first to check if those are working. If someone has a more technical advice on how to measure the diodes to check their integrity? I do have a multimeter with me.
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Posted By
JamesC
on 2017-10-31
17:47:32
| Re: Commodore 16 and 'Device Not present' error :-(
Yes, there are a set of diodes in line between the serial bus connector and the CPU. To test, apply 5V at each pin of the serial bus connector (where you attach the disk drive cable), and see what voltage comes through to the CPU's side of the corresponding diode.
Refer to the bottom of this technote.
When I said no single chip controls the serial bus, I meant that we cannot just say "replace this one chip and be done". Since the 16 "boots up" I seriously doubt there is anything wrong with the CPU.
It's much more likely that the serial bus connector itself has developed a loose connection, which will be revealed when you try to pass voltage through it.
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Posted By
repetto74
on 2017-10-31
18:04:56
| Re: Commodore 16 and 'Device Not present' error :-(
Hi JamesC
Hoping that the 87501 is not damaged is a kind of relief for me . I will check the doc you sent me and try to measure components integrity. I will check also the PCB for bad solder joint or cracks. Is is not risky to apply 5 volts to each PIN?? You mean if I power up the C16, it will provide 5V to the serial port right?
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Posted By
JamesC
on 2017-11-01
11:18:09
| Re: Commodore 16 and 'Device Not present' error :-(
You wouldn't apply 5V to all pins at the same time! 5V to the connector's pin 1, test for 5V on the opposite side of pin 1's diode, then move on to pin 2.
If your meter can supply and measure a lower voltage, feel free to do that lower voltage. But the entire C16 operates on 9V DC, so there's no harm if the 5V you apply for testing would "slip past" and encounter another component, such as the CPU.
Also, test the power supply itself -- the specs are on the case, but you need 9V DC coming out. If you get significantly less, your C16 can go very wonky indeed. 
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Posted By
siz
on 2017-11-01
04:18:32
| Re: Commodore 16 and 'Device Not present' error :-(
In the summer I've repaired a plus/4 for one of my friend: it had a faulty CPU. Everything worked fine except the serial bus. Replacing the CPU solved the problem in that case.
Unfortunately it's really hard to find these and what can be found is overpriced. In my case I took it from an other plus/4 which had some rust and faulty TED.
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Posted By
repetto74
on 2017-11-01
07:39:15
| Re: Commodore 16 and 'Device Not present' error :-(
I have checked the output of the PSU and I have a weird reading around 15V ??? This thing is supposed to output 9.5 V DC but this is not the case. The C16 should have fried with this high voltage output so I do not understand.
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Posted By
repetto74
on 2017-11-01
07:40:49
| Re: Commodore 16 and 'Device Not present' error :-(
It is even more puzzling because when I measure the voltage input of the SD2IEC reader when connected I do have a 5.4 V DC which is the correct output required.
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Posted By
siz
on 2017-11-01
12:36:26
| Re: Commodore 16 and 'Device Not present' error :-(
The plus/4 PSU (just like the C64 one) provides 5V DC and 9V AC. Perhaps you measured the AC as DC.
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Posted By
repetto74
on 2017-11-01
18:11:26
| Re: Commodore 16 and 'Device Not present' error :-(
The PSU has written on it only 9.5 DC 800ma but clearly stating it is a PSU for the C16/116 only. The multimeter is set to DC voltage and measuring the input DC 2.1 mm connector will give 15V.
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Posted By
Ken
on 2017-11-01
20:00:18
| Re: Commodore 16 and 'Device Not present' error :-(
the 15v reading is the unloaded voltage
once you add a load to it , it will drop down very close to the 9.5v
almost all wallwarts do that
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Posted By
repetto74
on 2017-11-02
11:27:05
| Re: Commodore 16 and 'Device Not present' error :-(
Hi Ken,
I am not a noob on electronics but in fact I did not tested PSU giving different voltages so thank you for explaining how this work . The next move will be to test the TLL at U9 as this can be involved also in serial malfunctions.
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Posted By
MMS
on 2017-11-02
13:27:56
 | Re: Commodore 16 and 'Device Not present' error :-(
If I do undertsand you well, finally turned out the C16 PSU is the problem here.
As far as I know, the ZX Spectrum (and Timex) PSU brick provides exactly the same voltage and polarity as the C16 requires, and as I know, the jack connector size is also the same.
(it is a kind of interesting, as the C16 (116) planned to be a cheap ZX Spectrum competitor, so an expensive (C64 type dual voltage, expensive connector+socket) PSU does not help to keep costs down. A better designed, more robust 9V brick could do the same job in the Plus/4, as in the Spectrum +2, that has a 2.1A rating on a single jack...But they choose that crazy square connector for the PSU you cannot buy anywhere now...)
I run my ZX Spectrum (bough cheap with broken PSU) with a wallmart general PSU, it works, but not perfect. It is rather hard to get a general PSU with the right rating, or it become very expensive.
I have a Spectrum printer, but becase my wallmart can provide only 1.1A instead of the ZX Spectrum original 1.5A, the printer does not work.
I think this one will do the job, if you are in UK, but a UK adapter is easy to find
http://www.ebay.co.uk/itm/Sinclair-ZX-Spectrum-48K-Replacement-Power-Supply-PSU-9V-DC/182263781563?epid=918710678&hash=item2a6fc498bb:g:eTUAAOSwknJXxxYe
And as an evidence, there are ZX Spectrum power bricks advertised with "C16 compatibility"
(this one is more expensivve, but can be used in different countries too)
https://www.ebay.co.uk/itm/Sinclair-ZX-Spectrum-Replacement-Power-Supply-48k-128k-Toastrack-2-Grey-C16-PSU/231604434148?hash=item35ecb334e4:g:Z1EAAOSwHnFVjG1M
If you are in the US, then the Timex PSUs will do the job, but probalbly the Timex 1000 (=ZX81) PSU has lower 1.0A rating (I do not know, if it is enough for the C16)
https://www.ebay.com/p/Vintage-Timex-Sinclair-1000-Personal-Computer-With-16k-RAM-Module-1016/1274029585?iid=112609945352
Actually this one looks the most robust one, but the most expensive at the same time (no surprises).
If you are within EU/AT, then you just connect your standard mains cable, and ready to go
It is regulated, so the C16 will not warm up so much, and has some protection, not to mention the switch :-)
(OK, the switch needed for the ZX Spectrums only)
http://www.ebay.co.uk/itm/Sinclair-ZX-Spectrum-High-Quality-Replacement-Desktop-Style-Power-Supply-PSU/263258446526?hash=item3d4b6d1abe:g:ojsAAOSwSRlZ3nRj
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Posted By
repetto74
on 2017-11-02
15:38:19
| Re: Commodore 16 and 'Device Not present' error :-(
Hi MMS,
Thanks for your advice. Actually I do not think the PSU is at fault. When measured at the SD2IEC power input pin when the C16 is powered up, I do have 5.4V which is the required voltage.
I would have fried my C16 by this time if the PSU was outputting an overvoltage. Having said that I am not an expert and do not know how a potential PSU malfunction can stop the serial port from working properly with the C16 running normally.
I have desoldered the U9 and U7 as those two TLL are reported being common C16 fault.
I have also finally managed to pick up a working loose Plus/4 (with no power supply) for a few bucks only. Luckily this one may have the CPU and TED in good working order in case I will need to Swap . I was also considering to may shelve the C16 and play more with the Plus/4. Both machines are equal, only difference are the memory available on the Plus/4 and the embedded programs into ROMS.
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Posted By
MMS
on 2017-11-02
18:10:00
| Re: Commodore 16 and 'Device Not present' error :-(
Hi,
Maybe the C16 is a little better for the robust keyboard and the more space inside, means less heat for the ICs. If you could make the C16 somehow 64KB machine, you will soon forget the built-in programs in the ROM, I mean demos, games and GEOS are all much more fun than that PRG
If you are lucky, then you have a Plus/4 with round/circle PSU connector like me.
Then any C64 PSU will help you. If it is the mentioned square connector, then I should wish you good luck, but it will be hard to get such a PSU, and the C64 round --> Plus/4 square adapter itself is a challenge.
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Posted By
repetto74
on 2017-11-02
19:13:37
| Re: Commodore 16 and 'Device Not present' error :-(
Hi MMS,
Finger crossed then  . I will consider anyway the 64k mod of the C16. Is there any tutorial explaining this?
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Posted By
repetto74
on 2017-11-03
07:25:04
| Re: Commodore 16 and 'Device Not present' error :-(
Hi,
The problem has been fixed !. It turned out to be the 7406 logic at U7. Replacing that has cleared the Device Not Present error . Glad not to have CPU or TED faulty here !!
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Posted By
JamesC
on 2017-11-03
09:17:46
| Re: Commodore 16 and 'Device Not present' error :-(
Good to hear that you found the cause, and that it wasn't an expensive repair.
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Posted By
repetto74
on 2017-11-03
10:31:12
| Re: Commodore 16 and 'Device Not present' error :-(
Yep that's great! I will receive also a spare Plus/4 just in case
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