HP LJ4M slow switch on

Probably dried out electrolytic caps. You should measure their ESRs to know which ones need to be changed. If there is not very lot of caps, you can also try to change them all, except the one(s) as main filter right after mains rectification.

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You'd replace a HP laserjet with a crappy inkjet?! Wow..

I believe the proper last sentence is "It's not worth me getting a new power supply with laser printers being so cheap these days".

I had an inkjet, an Apple Stylewriter bought used for twenty dollars in 2001. When I filled up the ink cartridge, I was really disappointed by how little I could print before I had to refill. And I realized early on that the ink so easily smears when it gets wet.

A few months later, I got an old TI laser printer for $25 at a school rummage. That lasted a while, but when it ran out of ink, I was uncertain about it's state so I simply replaced it with another used laser printer. The second one cost me only $15, but it was an HP Laserjet

4P. It had fewer pages on it than the TI, and had no problem from the start (unlike the TI that had some slight printing problem that might have simply been the lack of toner). It's lasted longer than the TI in my hands, and I don't foresee it going bad.

But if it does, I'll simply buy another used laser printer for about the same amount. And if those run out, I can buy a laser printer new for under a hundred dollars, which is far less than I paid for my first dot matrix printer in 1982, or my first daisywheel printer in 1984.

Michael

I just bought a Brother all in one laser for about $110 after rebates. Cheaper than the replacement drum unit!

My first "Printer" was a pair of heathkit H-14 printers, in pieces in a box for $20 at the Cincinnati hamfest in 1983. Both were missing the masked ROM CPU, which set me back another $30. It was RS-232 with square print wires, but it did a nice job. I found out later that it was the same printhead and drive motors used in Diebold ATMs, and dug about

20 defective ATM printers out of their dumpster when I worked next door to their service center in Orlando. I still have a few good, spare print heads, somewhere. ;-)

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Member of DAV #85.

Michael A. Terrell
Central Florida

Lasers are plenty cheap these days as well. The HP Laserjet 1020 is very inexpensive if you do a little shopping around.

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The Centennial miniseries, http://centennial-dvd.com

Thanks for the suggestion Simoc.

I had thought of caps but if it's been on 24 hours previously it only takes 2 seconds before powering up yet if it's been a week it takes 2 minutes. Can you see a cap in the power supply not fully discharging in

24 hours? Then there is the ten years I've had the printer and it's occasionally gone a couple of weeks between being used, surely the caps would have discharged in that time and I would have seen the same problem.

I was thinking more along the lines of a battery to be honest, maybe on the processor board. There isn't any obvious damage to the psu and no caps are leaking or bulging.

Thanks also to all who suggest I stay with laser printing :-)

This one has done sterling work and was a real second hand bargain when I got it. Times change though and I'm now effectively a home user who may want to print the occasional web page or letter and possible photographs in the future. Even a modern cheap laser will do something like 2000 sheets from a toner cartridge and I just can't see me printing that much in the next 10 years.

I'm not dumping this printer while it still works though and I can't see me buying an inkjet while this does still work. Lasers are real value for money printers providing you use them but the consumables do so many sheets that I'm never going to use them up. The previous toner cartridge didn't run out of toner, the transfer roller aged first and I was using it a lot more than I do now.

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Regards - Rodney Pont
The from address exists but is mostly dumped,
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You're welcome.

Bad caps cause exactly that kind of behavior. You just have missed some of the theory, I explain:

You are probably thinking, that the 2 mins would be normal when they're discharged. But not, that's not the point. If the caps were good, they would charge virtually immediately when powered, even if they're fully discharged. That explained your last sentence (as then the caps weren't dried out yet).

But as they are now dried out due to aging, their ESRs have increased and that reduces both the charge and discharge current, causing too much ripple voltage (and thus preventing the device from working). They probably get discharged within 24h, but the point is there, that those caps get _temporarily_ "rejuvenated" (ESRs decrease) when power is applied for long enough time (the 2 min), by causing them to heat up. But once the device is turned off, the caps cool down and then the "rejuvenation" begins to lose its effect (ESRs begin to increase again) _slowly_ (not immediately when cooled down and discharged, but within a few days).

So the dried out caps should be replaced with new ones. Easy repair :-)

What battery? If there is one (I'm doubting), it's for memory back-up and if bad, it would cause the device not to remember settings when disconnected, but it doesn't cause the delayed start-up.

Bad caps don't bulge nor leak in most cases (although sometimes do).

-- Top-posting not supported.

I understand that now, just like a car battery that's duff could have virtually no charge when cold but when warmed up works. I wasn't looking at it from that point of view, I was just thinking how could a change of capacitance affect performance depending on how long it had been off, as you guessed :-)

There is only about half a dozen electrolytic caps and it's only a single sided board so I'll take them out and test them. You said not the mains filter cap(??), there is a 400V 1000uF (or 100uF can't remember which) in there and I assume that's the mains one and it may have a slight bulge on the top. Any particular reason not to go near that one?

Thanks again, I'll go inside it again sometime, hopefully before I need to print something.

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Regards - Rodney Pont
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please send any emails to the address below
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Ok, do you have an ESR-meter? I want to highlight, that the capacitance measurement doesn't tell reasonably the condition of the cap, as the capacitance very rarely goes out of tolerance when the cap goes bad. It's the ESR (equivalent series resistance) instead, like I've already mentioned. It increases due to aging.

If you have an ESR meter accessible, good. But if not, your chances to deal with this case are:

-to buy one

-to build one:

-to just replace all the caps with new ones

-to test the caps by using a function generator and an oscilloscope instead

The latter method is done by tuning the gen to a high freq, something around 50kHz, with 100-200mV amplitude, connecting the cap in series with the gen output and scope input, and scoping if the cap causes significant attenuation by comparing the amplitude with and without the cap in series.

Yes.

Not for not going near it. I just meant that if you decide to do the method of replacing all the caps (if you haven't equipment for testing them), then I would leave the mains one alone, as they fail very rarely, and are also the least critical. So the small ones in chopper circuits are both far faster to decay with age, and also much more critical, and a small ESR on those can cause an appliance to completely cease working, while the mains one in many cases outlast the device in good condition, and might work well even with slightly increased ESR.

I've never experienced a mains cap having to be replaced except in over

30 years old antique equipment.

But however, I'm still not claiming that it couldn't fail, and if you are suspecting it, replace it too if you're still gonna do the replace-them-all-method. But if you are gonna make ESR measurements, of course, the mains one should be measured as well, and treated according to it. But some caps (especially those bigger ones) look like "little bulged" just normally.

--
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I knew absolutely nothing about ESR. I'd seen it mentioned here but never thought to look into it. I suppose as a field tech I wasn't expected to diagnose to that level but even when I sent things to the workshop the only feedback I used to get was 'we replaced them until it worked'. I don't think I ever managed to fix a switched mode PSU and even on days I spent in the workshop I avoided them. My problem was all the components seemed to test ok and I bet it was ESR... I can't say how grateful I am for the lesson and I think I've just got to build a meter :-)

A couple of years ago I was given a Sony 25inch TV with the picture folding over but even knowing it's bound to be a capacitor I've put off looking at it...

Thanks again.

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Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail	ngpsm4 (at) infohitsystems (dot) ltd (dot) uk

You're welcome. Btw, I really recommend building the meter on the Homo Ludens site, I've built that, it works very well and is very useful.

Good luck :-)

-- Top-posting not supported.

Forgot to say, that you can see approx. highest acceptable ESRs of new caps here:

It's acceptable that they rise a little, from those values but how much, depends of the purpose...

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I recommend this ESR meter:

I have not tried the Ludens one.

Chris