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Old 7th Mar 2024, 7:34 pm   #81
SiriusHardware
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Default Re: Commodore 8026 printer / typewriter

We look forward to seeing your trademark hand-drawn full circuit diagram in due course, Tony.
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Old 7th Mar 2024, 8:36 pm   #82
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Default Re: Commodore 8026 printer / typewriter

I seem to remember there was something in the German manual about settings being retained for a while after power off - perhaps that's what the batteries were for?

https://archive.org/details/cbm8026_manual_german

I'm away but will look more when I'm home.

Colin.
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Old 8th Mar 2024, 2:18 am   #83
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Default Re: Commodore 8026 printer / typewriter

Although TonyDuell had said this had a special development processor, with external piggy-backed EPROM that appeared to not have the internal RAM backup supply input - only an I/O port on that pin.

Which does seem strange why they'd fit those batteries in that case, unless they also supply an external SRAM IC.
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Old 8th Mar 2024, 5:27 am   #84
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Default Re: Commodore 8026 printer / typewriter

There is some external RAM on the board, but it's not low-power (a pair of 68A10 chips). I don't think it's battery-backed. It's possible the intention was to use the processor chip with the battery-backup pin but that early models (all models?) ended up with the development processor fitted. It's in a socket so the board would have been soldered without the processor, probably all boards made the same.

More when I've produced a schematic....
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Old 8th Mar 2024, 12:15 pm   #85
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Default Re: Commodore 8026 printer / typewriter

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Originally Posted by ScottishColin View Post
I seem to remember there was something in the German manual about settings being retained for a while after power off - perhaps that's what the batteries were for?
The manual says the settings are maintained for 70 - 90 hours. Doesn't sound very long if that's what the battery is for. I suspect the battery is for something else.
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Old 8th Mar 2024, 12:29 pm   #86
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Default Re: Commodore 8026 printer / typewriter

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Originally Posted by ScottishColin View Post
I seem to remember there was something in the German manual about settings being retained for a while after power off - perhaps that's what the batteries were for?
The manual says the settings are maintained for 70 - 90 hours. Doesn't sound very long if that's what the battery is for. I suspect the battery is for something else.
Although maybe the batteries would power the higher-power 68A10 IC's for about that time? So they might have done this in lieu of having a processor with built-in low-power RAM.
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Old 8th Mar 2024, 4:38 pm   #87
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Default Re: Commodore 8026 printer / typewriter

I don't think the batteries power anything other than the internal processor RAM on the chip that has that facility. The board seems to have been designed for that chip, another pin which is a port on the development processor has a capacitor to ground. It's a substrate decoupling pin on the one with battery-backable RAM.

But we shall see.

A couple of worrying things so far. The batteries are charged from the 9.5V line, they act as a shunt regulator to limit the voltage. So with dead/no batteries in the thing, that port pin will have been taken to too high a voltage for comfort. I hope it's not done much damage. Mind you, the development version of the processor is hard to find but I'll bet it's a lot more common than a mask-programmed one for such a printer.

Other problem. There are a couple of resistors in the daisywheel motor driver circut on th carriage that are burnt out. Test totally open-circuit on my meter. I can make out the remains of a red band, so probably 22-something.

Given the supply is 39V, a 2k2 conncted across it would disipate about 0.7W. Likely to burn out a small resistor, but these look well cooked. So I am guessing 220 ohms or maybe 22 ohms.

Did we ever determine if the original batteries were 1 or 2 cells each?

Other minor problem is that I only have the PCBs, not the rest of the machine. Obvously shipping it was impractical. I am therefore unable to be sure about some of the mechanical bits. For example there's a 6 pin connector that goes to at least one microswitch (paper out?). In fact the microswitches seem to be read as part of the keyboard, there are 3 keyboard column and 3 keyboard row lines there. So it could handle up to 9 microswitches, although given anti-sneak-path diodes are on the main logic board, probably only 3 would be used. But no idea what they would be for.
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Old 8th Mar 2024, 6:22 pm   #88
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Default Re: Commodore 8026 printer / typewriter

Very quick update. There were 2 components mentioned early in this thread that had been corroded by battery leakage. A resistor and a transistor.

They are both part of the power-OK reset/enable circuit. The remains of the resistor measures about 560 ohms and that would make sense in the circuit. The transistor we knew to be PNP (which again makes sense), I think a BC337 is a likely candidate (especially given the BC237s that are all over the boards!). Towers give an Ic(max) of 800mA for that which I think is sufficient.

No battery backup of the 68A10 RAMs. The only place the battery output links to is the appropriate pin (you know what I mean) on the processor.

And a correction to the last message. Turns out 2 of the diodes for the microswitches got to the same column line, so 6 switches maximum. Most likely to be limited to 3 as I said, maybe not all used
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Old 8th Mar 2024, 8:42 pm   #89
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Default Re: Commodore 8026 printer / typewriter

Oops... I meant a BC327 (PNP) transistor...
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Old 9th Mar 2024, 1:06 am   #90
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Default Re: Commodore 8026 printer / typewriter

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Originally Posted by TonyDuell View Post
>>
>>
Did we ever determine if the original batteries were 1 or 2 cells each?
>>
Well I reckoned they were most-likely 2 cells per batteries, in one of my previous replies (post #31),here : https://www.vintage-radio.net/forum/...3&postcount=31
- In reply to Colin's photo's, in his post #7, here: https://www.vintage-radio.net/forum/...69&postcount=7

So 2 x 1.2V cells in each x 2 batteries would make 4.8V which seems about-right for a 5V device port-pin.
But to be 100%, would require batteries to be resurrected a bit, with a high-current pulse to remove any shorts that NiCd's can be prone to, to allow them to be charged a bit to read a voltage from them.
- Or to make a small cut in middle of the (heatshrink) on the original batteries, to see if there really is a join between two separate (N-size?) cells).

It does seem very odd to fit batteries in something that doesn't have LP RAM powered by it - especially if the manual suggested 70hrs backup.
Would have been cheaper to have fitted a zener doide plus maybe increased charging resistor value from 9.5V supply (or just connect pin to 5V, instead).
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Old 9th Mar 2024, 12:30 pm   #91
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Default Re: Commodore 8026 printer / typewriter

Thanks for the updates. I've been watching from a distance.

I've opened up one of the battery packs and attach three photos.

As previously surmised, each battery pack is 2 cells. No markings on the side of the batteries, but on the end, it's marked as 188A.14. Each battery is 15mm in diameter and approx 27mm long.

Colin.
Attached Files
File Type: zip PXL_20240309_112009974.zip (1.33 MB, 29 views)
File Type: zip PXL_20240309_112541921.zip (1.21 MB, 26 views)
File Type: zip PXL_20240309_112416775.zip (1.24 MB, 25 views)
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Old 9th Mar 2024, 2:49 pm   #92
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Default Re: Commodore 8026 printer / typewriter

Quote:
Originally Posted by SiriusHardware View Post
We look forward to seeing your trademark hand-drawn full circuit diagram in due course, Tony.
And here you are. Schematics of the logic board, GPIB board that's wired to it, and the boards in the printer carriage. That's all I was sent.

A couple of things that might not be obvious :

The 'downwards E' is logic ground. With a 'P' alongside it it's the power ground. These are linked in the power supply.

The Addr() bus comes from a port on the processor. As such it is used not only to address the 256 bytes of external RAM but also as status _inputs_ to the processor.

Colin : I've fitted a 560ohm resistor, but I don't have a BC327 that I can find. I've also lifted one end of a diode from the battery backup circuit so that will no longer overvoltage the processor if there are no batteries fitted. I suspect it will work like this, assuming no other faults.
Attached Files
File Type: pdf CBM8026_Logic_Schematic_144dpi_75%.pdf (2.07 MB, 39 views)
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Old 9th Mar 2024, 4:21 pm   #93
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Default Re: Commodore 8026 printer / typewriter

Quote:
Originally Posted by ScottishColin View Post
Thanks for the updates. I've been watching from a distance.

I've opened up one of the battery packs and attach three photos.

As previously surmised, each battery pack is 2 cells. No markings on the side of the batteries, but on the end, it's marked as 188A.14. Each battery is 15mm in diameter and approx 27mm long.

Colin.
It looks like these are actually '2/3 AA' size, which appear to be just over 14mm dia and around 28mm long: https://power.tenergy.com/battery-size-chart/ (The N size ones I thought they might be appear to be 12.0mm in diameter and 30.2mm in length)

Many places sell 2/3 AA NiMH replacements for original NiCd? ones.
But you'd really need to battery-tag weld joining strips between the two (then fold them to be in-line) / PCB pin contact end terminations onto them - unless there is a fully ready-made 2 in series drop in replacement available.

However, as it seem the battery doesn't really do anything in this, then might not be really worth replacing as it was
- especially with risk of PCB damage from leakage.
Although, you could always just get a 4xAA battery holder and remotely-mount 4x NiMH AA cells in the unit, assuming there a space somewhere else for this.
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Old 9th Mar 2024, 5:20 pm   #94
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Default Re: Commodore 8026 printer / typewriter

If it were mine, I'd find a way to use it without batteries. My guess is that they do nothing anyway with this version of the processor chip. Even if they do keep some settings overnight, it's not long enough to be useful and re-loading the settings is presumably not hard.

When I send the boards back to Colin, I'll have disconnected one of the diodes from the battery. My suggestion is that he tries it like that, if it works then run it like that with no battery, etc.
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Old 9th Mar 2024, 8:43 pm   #95
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Default Re: Commodore 8026 printer / typewriter

Thanks so much Tony - I have BC327s here so that's no problem.

Could you identify which two resistors need replacing please as per post 87 and I'll sort them.

I'm very grateful for you efforts. I can't see the need to replace the batteries if I'm honest.

Colin.

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Quote:
Originally Posted by SiriusHardware View Post
We look forward to seeing your trademark hand-drawn full circuit diagram in due course, Tony.
And here you are. Schematics of the logic board, GPIB board that's wired to it, and the boards in the printer carriage. That's all I was sent.

A couple of things that might not be obvious :

The 'downwards E' is logic ground. With a 'P' alongside it it's the power ground. These are linked in the power supply.

The Addr() bus comes from a port on the processor. As such it is used not only to address the 256 bytes of external RAM but also as status _inputs_ to the processor.

Colin : I've fitted a 560ohm resistor, but I don't have a BC327 that I can find. I've also lifted one end of a diode from the battery backup circuit so that will no longer overvoltage the processor if there are no batteries fitted. I suspect it will work like this, assuming no other faults.
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Old 10th Mar 2024, 8:28 am   #96
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Default Re: Commodore 8026 printer / typewriter

As I mentioned in my last PM to Colin, I've found an RS bag of new BC327 transistors here. I remember buying BC337s for a repair in the past, I guess I bought the PNP one too. I'll fit one while the board is on my bench.

The burnt out resistors are on the carriage PCB, near the 20 pin ribbon cable connector. I think they were 220 ohm, but am not sure, could be 22ohm.
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Old 10th Mar 2024, 9:46 am   #97
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Default Re: Commodore 8026 printer / typewriter

Just looked at the diagrams, Tony, you did very well to work all that out in such a short time, clearly that is your superpower.

Those drawings will go a long way towards (hopefully) making this work again.
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Old 10th Mar 2024, 3:05 pm   #98
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Default Re: Commodore 8026 printer / typewriter

I will run it without batteries I think. if we can get through to the other end of fixing this, I may put them back just cosmetically but there's probably quite a bit of work to do yet.

At least one of the cogs has split so I need to print a new one to replace that for a starter.

Colin.

Quote:
Originally Posted by TonyDuell View Post
If it were mine, I'd find a way to use it without batteries. My guess is that they do nothing anyway with this version of the processor chip. Even if they do keep some settings overnight, it's not long enough to be useful and re-loading the settings is presumably not hard.

When I send the boards back to Colin, I'll have disconnected one of the diodes from the battery. My suggestion is that he tries it like that, if it works then run it like that with no battery, etc.
Attached Files
File Type: zip PXL_20240108_200006583.zip (1.99 MB, 28 views)
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Old 10th Mar 2024, 4:18 pm   #99
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Default Re: Commodore 8026 printer / typewriter

While it was on my bench I made a dump of the firmware. Being the development processor, this was easy, the firmware is in a 2532 EPROM plugged into the top of the processor package and my Ferret programmer handles that sort of chip without problems.

The attached .zip file contains the Intel hex file from my programmer and a binary file which should be exactly 4096 bytes long.
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File Type: zip cbm8026.zip (6.0 KB, 25 views)
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Old 10th Mar 2024, 5:06 pm   #100
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Default Re: Commodore 8026 printer / typewriter

Were you able to definitively identify the processor that sits underneath the EPROM?

Colin.

Quote:
Originally Posted by TonyDuell View Post
While it was on my bench I made a dump of the firmware. Being the development processor, this was easy, the firmware is in a 2532 EPROM plugged into the top of the processor package and my Ferret programmer handles that sort of chip without problems.

The attached .zip file contains the Intel hex file from my programmer and a binary file which should be exactly 4096 bytes long.
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