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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 16th Apr 2024, 11:10 am   #221
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

I do have one of these that I bought to power the MK14 I have. It has a useful set of connectors including one that I can use to separate the wiring and use with a breadboard.

However we're taking advantage of me having some time off and going north for a few days in the motorhome.

I'll test it when I return before I put anything back into the motherboard, along with the tests in post 200 on the new chip.

Colin.
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Old 16th Apr 2024, 11:25 am   #222
SiriusHardware
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Default Re: Commodore 8026 printer / typewriter

That's potentially very useful with that 'break-out-to-screw-terminals' fitting that can go on the end, and I see it does have a 5V output setting. It will almost certainly be a regulated SMPSU rather than an unregulated linear supply, but best to check that the '5V' output really is 5.0V or near enough before connecting it to anything else.

Enjoy your trip away, wish I could do the same, I have not done my regular trips up to the northwest for a couple of years now, due to circumstances closer to home.
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Old 18th Apr 2024, 7:47 pm   #223
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Default Re: Commodore 8026 printer / typewriter

Evening. Home. Replacement 7404 (actually a TI SN7404N) fitted.

Steady reading now of 0.107A.

Time to put all the legs of the BC327 back in?

I will also do the test suggested in post 218 later on.

Colin.
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Old 18th Apr 2024, 8:37 pm   #224
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Default Re: Commodore 8026 printer / typewriter

Yes, reinstate the 327 properly and let's see how warm it gets now. Keep an eye out for other things getting hot, especially those resistors.
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Old 19th Apr 2024, 4:28 pm   #225
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Default Re: Commodore 8026 printer / typewriter

I have put the BC327 back in. Unfortunately due to the number of times I have removed/reinstalled it, the pad has gone so I have put a patch wire in under the board which connects the C pin to pin 38 of the CPU socket (U9).

Having powered it on with just the PSU plug, the earth leg and no other connectors fitted and also with U9 (main board) and U1 (IEEE488 board) removed, I get no heat like before.

There is one resistor which eventually goes to about 40 degrees C (129 ohm resistor which is original and has not been replaced) but is not hot to the touch.

Could someone please confirm that the patch to Pin 38 of U9 is correct for the collector leg of the BC327 please? I had previously stated pin 17 but I think I must have mis-counted as the socket is the other way up from other sockets so I managed to get that wrong.

Colin.
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Old 19th Apr 2024, 5:33 pm   #226
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Default Re: Commodore 8026 printer / typewriter

I can't find the pinout for the microprocessor just now but the collector of the 327 should go to one end of the nearby 120R resistor, the end of the 120R which doesn't go to 0V.

As long as your 327 collector is connected directly to one end of that resistor it should also be connected to the correct (reset) pin of the microprocessor, unless the track between the resistor and the microprocessor has somehow been damaged.
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Old 19th Apr 2024, 5:59 pm   #227
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Default Re: Commodore 8026 printer / typewriter

Confirmed that I have continuity from the collector to the non-zero V end of the 120 ohm resistor (that's the resistor that got a little warm).

Colin.
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Old 19th Apr 2024, 6:00 pm   #228
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Default Re: Commodore 8026 printer / typewriter

From this data book on bitsavers:-

http://www.bitsavers.org/components/..._Data_Book.pdf

I got the attached pinout table for the MK387x series although the MK3874 specifically is not in the table, typically.

This would appear to say that pin 39, not pin 38, is the RES pin on the microprocessor. Measure between the non-0V end of the 120R and pin 39 of the microprocessor and if you see a direct connection, that's probably correct.

Just read your last - I would expect that resistor to get comfortably warm. Now you should find that the 327 collector and the end of the 120R that it is connected to are also connected to the RES pin (pin 39?) of the microprocessor.
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Old 19th Apr 2024, 7:45 pm   #229
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

OK. My error again. My only excuse is that there are pads on the underneath of the motherboard that are exactly in line with the 40 pin socket so I had assumed there were socket.

I have continuity from the 120 ohm resistor and the 327 collector to both pins 39 and 40 of the socket.

I have removed the processor and tested underneath and have continuity directly between pins 39 and 40 of U9.

I hope that's ok?

Colin.
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Old 19th Apr 2024, 8:30 pm   #230
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Default Re: Commodore 8026 printer / typewriter

Hmmm.

If the pinout I posted is correct then that would have the 5VSW line going to both RES and the +5V supply pin of U9. When Tony listed all of the placed which 5VSW goes to in an earlier post (#186) he only counted RES on U9 and didn't state that it also went to the +5V supply pin.

If you are sure pin 39 is connected to pin 40 I think we need Tony's opinion on this - it's not impossible that U9 is one of the chips which has its supply pin, as well as its reset pin, switched by the 327 but I didn't see anything that suggested so earlier, unless I missed it.

Of course, the pinout I found could be wrong and pin 40 may not be the chip's +5V supply pin - Tony obviously had a pinout that he was working from so we'd better see what he says.
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Old 19th Apr 2024, 8:53 pm   #231
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Default Re: Commodore 8026 printer / typewriter

Just looking at the diagram, only 38 pins of the processor are accounted for, the ones not shown being the +5V supply pin and the 0V supply pin - so we don't know from the diagram where the +5V supply for pin 40 (VCC) actually comes from - normally when they are not explicitly shown the power pins of a 5V logic IC can be assumed to be connected to 0V and hard +5V - but in this case it may be that U9's VCC pin is supposed to be connected to 5VSW, as indeed the VCC pins of some of the other logic ICs are.
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Old 20th Apr 2024, 9:46 am   #232
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Default Re: Commodore 8026 printer / typewriter

If I didn't show the power connections, it means they were conventional. In the case of the processor I am pretty sure they were +5V and ground. The similar Olympia typewriter that was mentioned earlier in this thread has the processor wired that way, I've just checked. You would not power the processor from +5VSW, the idea is that the processor is powered but held reset (rst/, connected to +5VSW, is low) then +5VSW comes up and the processor starts running.

It's possible I made a mistake when tracing the schematic out but it's something I would have checked and noticed.

Is there a short between +5V (on the connector from the power supply) and +5VSW?
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Old 20th Apr 2024, 12:10 pm   #233
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

I am going to remove the BC327 and test connections to both pin 39 and 40 of U9, and then onto the 5V pin of J3.

I will then install a new BC327 with the patch wire and perform the tests again and post my results.

I have been placing the patch wire between the connector leg of BC327 and pin 39 of U9. Is it better if I place it to the 120 Ohm resistor as per post 226?

I hope that makes sense.

Colin.
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Old 20th Apr 2024, 7:15 pm   #234
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Default Re: Commodore 8026 printer / typewriter

Electrically speaking, they are one and the same place (on the same circuit node, so all should have zero ohms resistance between them) so it doesn't matter whether you take the connection from the 327 collector to the 120R resistor or to U9 pin 39.

If your patch wire goes to pin 39 then I suppose there is a small chance that there might be a stray wire strand or solder hair connecting pin 39 to pin 40, always worth checking over when you happen to have done some solder work in exactly that area. Broadly speaking the best way to repair a track break is to repair it where it is broken, by effectively reinstating the original trackwork and the route it took.

There can be occasions when the routing of a track in relation to other tracks can be important, but for this particular track it won't be.

If you are still taking pads or tracks off PCBs occasionally I would honestly suggest investing in one of the modestly priced (Duratool? RS Pro?) electrical pump assisted desoldering irons - only problem is, once you have used one you'll be very reluctant to desolder anything any other way.
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Old 22nd Apr 2024, 12:52 pm   #235
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

OK.

New 327 in place.

Base and Emitter connections are the same as with the old one.

Connector leg has a solid connection (via the patch wire) to pin 39 of U9.

It now has a non-zero (320 ohm) connection to pin 40 of U9.

Is that OK?

Colin.
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Old 22nd Apr 2024, 1:01 pm   #236
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Default Re: Commodore 8026 printer / typewriter

That sounds correct. The 320 ohms is due to random conducting components on the circuit board between the supply lines (that 120 ohm resistor is probably part of it)
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Old 22nd Apr 2024, 1:06 pm   #237
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

OK - so all components are now back in place with the right connections and no temperatures look out of line to me when powered up.

What's the next step then? My scope is at the ready in case that's required.

Colin.
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Old 22nd Apr 2024, 1:15 pm   #238
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Default Re: Commodore 8026 printer / typewriter

Try connecting the carriage motor (J1) and the carriage (J4, the grey ribbon cable) and powering up.

My guess is that the thing should try to move the carriage to the left side home position (detected by the slotted opto-switch under the carriage). I'd be surprised if it all works, but it's worth seeing if it does anything.
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Old 22nd Apr 2024, 4:40 pm   #239
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

A short beep (which I believe is correct if that video is right), then nothing. No movement of the carriage or homing.

If I move the carriage by hand all the way to the left, something kicks in to push it back half a centimetre or so so I'm guessing the optical sensor is working correctly..

But no movement from the carriage motor.

Colin.

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Originally Posted by TonyDuell View Post
Try connecting the carriage motor (J1) and the carriage (J4, the grey ribbon cable) and powering up.

My guess is that the thing should try to move the carriage to the left side home position (detected by the slotted opto-switch under the carriage). I'd be surprised if it all works, but it's worth seeing if it does anything.
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Old 22nd Apr 2024, 6:16 pm   #240
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Default Re: Commodore 8026 printer / typewriter

Does the same thing happen if you slide the carriage all the way to the right? If it pushes back from both ends it may be that the carriage drive and motor are working.

If it does push back from either end then it could be that there's some kind of sensor interlock at play, which won't let the carriage be driven until some physical condition is satisfied like 'the lid is closed', or something like that.

Tony will have a better idea of what we are looking for in this respect.
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