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Old 2nd Jan 2024, 1:58 pm   #21
SiriusHardware
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Default Re: Commodore 8026 printer / typewriter

Look at the pads for the broken capacitors on the underside of the PCB. Does one end of each capacitor go to the 0V track and do the other ends go to other pins on that connector? Their proximity to the connector makes me suspect that they are supply rail decoupling capacitors.
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Old 2nd Jan 2024, 2:32 pm   #22
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

The same of each capacitor is connected to each other then onto an earthing wire that is bolted to the frame of the printer.

The other ends are connected to pins 2,3 and 4 respectively from post #20.

Colin.

Quote:
Originally Posted by SiriusHardware View Post
Look at the pads for the broken capacitors
on the underside of the PCB. Does one end of each capacitor go to the 0V track and do the other ends go to other pins on that connector? Their proximity to the connector makes me suspect that they are supply rail decoupling capacitors.
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Old 2nd Jan 2024, 7:06 pm   #23
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Default Re: Commodore 8026 printer / typewriter

OK, well, that reinforces the idea that they are just supply rail decoupling capacitors - their proximity to the power input connector and the fact that each one goes from a different supply rail connection down to a 0V track or plane very close by strongly suggests so.

I couldn't really make out much in the photo of the original capacitors because they were in such a bad way but if you remember them being light brown and circular then most likely any disc ceramic capacitors with a value between 0.1uF and 0.47uF will be close enough. They will need to be appropriately voltage rated of course, especially the one with almost 40V on it - so I would just make them all 63V DC rated or even 100V DC rated, as long as they will physically fit in the space available.

That German thread you found had some pretty good info in it - it mentions one of the supplies being 20V to 30V. I suspect that supply and the 10V+ '9V' supply are both unregulated, and that those measured voltages will decrease once the PSU is powering a load. The 5V output clearly is regulated and is only a little bit on the low side.

Can you see any evidence of there being a 9V regulator? There might be, and if so its exact +9V output voltage may be adjustable by a preset resistor, but if not it is probably an unregulated supply.
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Old 2nd Jan 2024, 9:01 pm   #24
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Default Re: Commodore 8026 printer / typewriter

Cricklewood only seem to have 50V, 500V or 1kV+ and I can't find the values you've mentioned.

eBay seems to be happier with 50V capacitors and not much else.

Where's your go-to place for this type of component?

Colin.
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Old 2nd Jan 2024, 9:08 pm   #25
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Default Re: Commodore 8026 printer / typewriter

Also the 9V pin goes to what looks like an NPN or PNP transistor and the legs are very suspect. I think I'll remove it and see what markings I can read.

Colin.
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Old 2nd Jan 2024, 9:58 pm   #26
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Default Re: Commodore 8026 printer / typewriter

Quote:
what looks like an NPN or PNP transistor and the legs are very suspect.
The one on the left of your image is a BC237A. The one on the right is also a BC...something, difficult to see from that angle.

0.1uF and 0.47uF are values commonly also stated in nF, so

0.1uF = 100nF
0.47uF = 470nF

You may find you have more choice if you look for those values. 50V will probably do, I would have liked to have left a little bit more headroom on the ~40V rail.

Last edited by SiriusHardware; 2nd Jan 2024 at 10:10 pm.
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Old 2nd Jan 2024, 10:10 pm   #27
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Default Re: Commodore 8026 printer / typewriter

From Cricklewood:

https://www.cricklewoodelectronics.c...Capacitor.html

Just reassure yourself that the original capacitors were this same style / shape of capacitor, if that is even possible given what is left of them.

There is also a blue Tantalum capacitor, looking very innocent, between the two transistors. Most people consider them to be replace-on-sight due to their habit of failing short-circuit but I would just check it to see if it is short-circuit and if it is not, let it be for the time being.
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Old 2nd Jan 2024, 10:43 pm   #28
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Default Re: Commodore 8026 printer / typewriter

Having looked at the photos you mentioned either of these, also from Cricklewood, might be a better visual fit for the originals. Watch out for the physical size though, look at the lead spacing in the specs and decide whether that is a good physical fit into the existing holes in the PCB.

https://www.cricklewoodelectronics.c...Capacitor.html

https://www.cricklewoodelectronics.com/CZF470N.html
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Old 3rd Jan 2024, 12:09 am   #29
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Default Re: Commodore 8026 printer / typewriter

Ordered. Thanks.

The Tantalum capacitors on the board have not shorted so I'll leave them be.

Colin.
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Old 3rd Jan 2024, 1:06 am   #30
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Default Re: Commodore 8026 printer / typewriter

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Originally Posted by ScottishColin View Post
Happy Christmas all.

I've been looking at the two 8026 PCBs today and I know they need cleaning up and the batteries removed, but I was thinking of drawing out the schematics as they don't seem to exist anywhere I can find.

I've never done this before so it may be a fools errand, but I was wondering if there is any software out there for beginners that will help with this?

Thanks.

Colin.
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Originally Posted by TonyDuell View Post
I've drawn out a few schematics over the years and have yet to find a CAD system which actually 'aids' me. Rather, I use what I call a 'paper aided design' system, or 'pad' (of plain paper).

My main tip for doing this is to find a way to identify the main components on the board -- the ICs, maybe transistors, etc. If they're labelled in the etch or silkscreen then use that, otherwise sketch a layout diagram (or take a clear photo) and number that.

Then make a list of said components and their sections (in the case of multple-gate ICs, for example). The list will be something like :
U1 6502
U2 a b c d '00 [I use 'xx to mean 74LSxx etc)
U3 2114
U4 2114
U5 '138
U6 a b c d e f '04
....


Start drawing out based on something known, like the processor. That's going to be used in essentally one way (it needs a clock signal, reset, will connect to the address and data buses, etc), whereas a NAND gate could be just about anything. As you draw out each device, cross it off the list. That way you won't forget a section, or do something twice.
Yes, I also usually do something similar - mostly always started by sketching it out on paper first. And then only ever resorting to Electronic-CAD using to draw a neater version to share it / allow a PCB to be re-created to make a replica (possibly with some mods) - Apparently some recent versions of (KiCAD?) PCB-CAD software allow you to include a transparent scaled-photo of each side of the board on the layout, to act as a template to lay the tracks etc. over.

My first paper draft is often more of a PCB placement + tracks connections diagram. So I draw the IC's as rectangular blocks with pins arranged as per the physical package. I then sometimes draw the internals inside the rectangle for logic IC's etc. That way it's easier to spot any connections you may have missed. Single / double-sided are often not too difficult to follow the tracks - except when they disappear under IC's etc. and you may need to start using continuity testing t confirm some guesswork (as is usually needed for > 2layer PCB's).
It is much easier to do this on a bare unassembled PCB, where you can scan the outer layers / sand down to inner layer, but can't really do this with rarer valuable vintage equipment that you can't just buy a fairly-cheap spare one to strip-down. With modern SMD ones, you also often need to remove all the unmarked components to measure them, to identify what value they are.

Once I'm sure I've captured all the track connections on this and worked out what all the IC's are, I then usually do a 2nd neater version, drawn more like a conventional schematic, to make it easier to follow.

In theory you could just start with a blank E-CAD software schematic sheet, with all the components (building ones not in supplied libraries as required - or just placing a snapshot of part's symbol, from the datasheet, to start with). And then connect them all up / re-arranging as required.
But I never got round to using any PCB software at home, as it was usually quite expense / were tied into proprietary formats that were hard to share / could end-up getting dropped in future.
However, I've been considering using the free open-source KiCAD, to avoid these issues, which can also import and export many formats, with some optional add-ons produced by users etc.

It's just a little annoying that the latest version for Windows is >= Win10 only, due to latest version of Python it uses ditching support for Win 7 before MS-support for it ended! (Although older Win7 etc versions of Python are still being updated concurrently with latest one, which makes you wonder why they released the latest >=Win10 only version).

But KiCAD is also available for many flavours of Linux, if you want to avoid Windows / want to carry-on using older P H/W that won't support Win11, once Win10 is dropped.

Spreadsheets of connections between parts can also be useful with more-complex designs, to help in cross-checking all the connectivity.
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Old 3rd Jan 2024, 1:34 am   #31
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Default Re: Commodore 8026 printer / typewriter

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Originally Posted by ScottishColin View Post
OK - batteries out to allow me to start cleaning.

They have three legs on them - see attached photos.

They are marked:

+188 8137
41B025AC00301
ASM IN MEXICO

Anyone recognise these?

Colin.

Looking at the photo of one of these batteries, it looks like there is a centre join between two ('N' size) 1.2V cells inside these ('AA-size' ?) batteries. So that would make each of these 2.4V.
(The use of 3 pins, with 2pins at one end, on these PCB-mount batteries is mainly to prevent them being inserted the wrong way round).

It might be possible to put some charge into them, to measure the nominal voltage, by connecting to a suitable PSU / series current-limiting resistor if PSU doesn't have a good adjustable constant-current limit.
But, frequently NiCad's often went short-circuit, due to internal dendrite crystal growths - However it is often possible to remove these by putting several amps through them for a very-brief (to avoid getting them too hot) by winding the PSU voltage up to a fair voltage and having current-limit set to a few amps / max limit if around that. It may be necessary to apply several quick pulses, before the batteries starts to read a voltage at rest.
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Old 7th Jan 2024, 5:41 pm   #32
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Default Re: Commodore 8026 printer / typewriter

OK - capacitors replaced and transistor out. I attach some close-up photos as I cannot make out the markings and would appreciate some help in working out what it is; is there any way I can test it to work this out?

Colin.
Attached Files
File Type: zip WIN_20240107_16_34_47_Pro.zip (44.3 KB, 32 views)
File Type: zip WIN_20240107_16_35_19_Pro.zip (59.6 KB, 33 views)
File Type: zip WIN_20240107_16_37_20_Pro.zip (63.5 KB, 39 views)
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Old 7th Jan 2024, 6:18 pm   #33
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Default Re: Commodore 8026 printer / typewriter

The markings look to be 'BC' followed by 3 digits. Of course we need to know what the digits are. Try photographing it from varous angles Try dampening the surface. You might be able to read the digits.

If not, all is not lost...

If you have one of those Chinese component testers or similar (I don't...) connect that to the 3 transistor leads and see what it says.

If you don't then you can make a start using the diode test range on a DMM. Test each pair of leads both ways round (so 6 tests). Hopefully the transistor is good and you'll get one of the following 2 results.

There is one transistor lead where if you put the red meter probe on it, you get a diode-drop reading (about 0.6-0.7V) on the DMM with the black probe on each of the other leads. That's an NPN transistor, the red probe is on the base.

There is one transistor lead here if you put the black meter probe on it, you get a diode-drop reading with the red probe on each of the other leads. That's a PNP transistor, the black probe is the base.

Now if your meter has a transistor test range, connect the transistor to the appropriate sockets. You know whether it's NPN or PNP, you know which the base lead is. Try the other 2 leads both ways round in the emitter and collector connections on the meter. One way will give a much higher gain than the other. That's the right one.

So you now know the pinout and polarity of the transistor.

Next trace out the circuit round that transistor. You should then get a good idea of the sort of voltage and current it's handling. Then you can find a replacement
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Old 7th Jan 2024, 7:50 pm   #34
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Default Re: Commodore 8026 printer / typewriter

So if I put the black lead (Common) on the centre pin and red on either outside I get a 0.6 reading.

That doesn't seem to match the words below, but I can get no other reading in any other combination of tests.

Connections on the attached picture - hopefully they're clear. Blue to blue (resistor), white to white (resistor). The Red pin goes to the +5V rail.

Colin.

Quote:
Originally Posted by TonyDuell View Post
The markings look to be 'BC' followed by 3 digits. Of course we need to know what the digits are. Try photographing it from varous angles Try dampening the surface. You might be able to read the digits.

If not, all is not lost...

If you have one of those Chinese component testers or similar (I don't...) connect that to the 3 transistor leads and see what it says.

If you don't then you can make a start using the diode test range on a DMM. Test each pair of leads both ways round (so 6 tests). Hopefully the transistor is good and you'll get one of the following 2 results.

There is one transistor lead where if you put the red meter probe on it, you get a diode-drop reading (about 0.6-0.7V) on the DMM with the black probe on each of the other leads. That's an NPN transistor, the red probe is on the base.

There is one transistor lead here if you put the black meter probe on it, you get a diode-drop reading with the red probe on each of the other leads. That's a PNP transistor, the black probe is the base.

Now if your meter has a transistor test range, connect the transistor to the appropriate sockets. You know whether it's NPN or PNP, you know which the base lead is. Try the other 2 leads both ways round in the emitter and collector connections on the meter. One way will give a much higher gain than the other. That's the right one.

So you now know the pinout and polarity of the transistor.

Next trace out the circuit round that transistor. You should then get a good idea of the sort of voltage and current it's handling. Then you can find a replacement
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Old 7th Jan 2024, 8:20 pm   #35
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Default Re: Commodore 8026 printer / typewriter

Quote:
So if I put the black lead (Common) on the centre pin and red on either outside I get a 0.6 reading.
It does actually match one of the results Tony suggested you might get:-

Quote:
There is one transistor lead here if you put the black meter probe on it, you get a diode-drop reading (0.6-0.7V) with the red probe on each of the other leads. That's a PNP transistor, the black probe is the base.
Given what you said, the middle pin of the transistor is its base and it is a PNP transistor. The markings look to me like BC??7. Unfortunately if it is a PNP type, then it is not the same as the other (BC237) transistor which is an NPN type.

Had they both been NPN it would have been reasonable to assume that they were probably the same general purpose type of NPN, but that sadly seems not to be the case.

Your measurements appear to suggest that, apart from having very short legs, the transistor is probably OK. You could just solder some stiff wire legs back onto the stumps and put it back into the PCB the same way around as it was originally. If you attempt this, keep the application of heat to the stumpy leads as short in duration as you can, to avoid thermal damage to the inside of the transistor.
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Old 7th Jan 2024, 10:51 pm   #36
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Default Re: Commodore 8026 printer / typewriter

I like the idea but the stumps are exceeding short and I'm struggling to get three wires/pins soldered to them.

I will continue but I was wondering how risky is it to make an educated guess at the transistor?

My best view is it's BC 67? but I can't be clear either and no amount of photography tricks nor cleaning are helping.

Colin.


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Old 8th Jan 2024, 5:41 am   #37
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Default Re: Commodore 8026 printer / typewriter

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Originally Posted by SiriusHardware View Post
Given what you said, the middle pin of the transistor is its base and it is a PNP transistor. The markings look to me like BC??7. Unfortunately if it is a PNP type, then it is not the same as the other (BC237) transistor which is an NPN type.
There is a BC337 which is PNP I think.
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Old 8th Jan 2024, 7:54 am   #38
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Default Re: Commodore 8026 printer / typewriter

Well if the 7 is really at the end, then maybe a BC557 or even a BC327 - which is rated higher than many 'low-power' BCnnn series TO02 transistors.
And (along with its BC337 NPN complement), was one of my favourite TO92 transistor to use back in the 80's for repairs & projects.

However, it did rather look like the 7 was in the middle of the usual 3 numbers following the BC.

You could maybe see what the manufacturer uses on other similar products, in case they like to re-use the same parts.

Or maybe look in a copy of Towers transistor substitution equivalents book (probably a pdf of this on the 'net somewhere) for likely BCx7x candidates (The old Cricklewood Electronics paper catalogue was also good for this, as they sold most transistor types and gave brief data on each. But I presume they've long since stopped doing these, although I should still have a copy somewhere).

Using the parametric search on Digikey / Mouser (Better than Farnell or RS etc) can also be useful to narrow-down possibilities - but the original ones may now be obsolete.

BCnnn etc 'registered type numbers' (rather than manufacturer-specific prefix type numbers) transistors were usually allocated in numerical order. So the oldest ones would normally start with 1nn, then 2nn etc. So try to find a match with BC17x then BC27x and BC37x etc. (Strangely, they seemed to have mainly skipped BC4xx, going to BC5xx. Then not many BC6xx, and no BC7xx?. BC8xx are usually surface-mount version).
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Old 8th Jan 2024, 5:44 pm   #39
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Default Re: Commodore 8026 printer / typewriter

I've got in contact with someone on VCFED who has a (non-working) 8026 and he has agreed to get his out and look at the components on his PCB to see if we can identify them that way.

What I am aware of is that I have seen at least two different 8026 PCBs so we'll have to wait to see if he has the same as mine.

Colin.
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Old 9th Jan 2024, 8:59 am   #40
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Default Re: Commodore 8026 printer / typewriter

If it's the same maybe you can also ask him to read the values of the capacitors you've replaced as well.
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