Zenith ZFL-181-92 with a little smoke - Page 1
Forum section: electronics / projects

author: FRParker
author_rank: Newbie
timestamp: April 25, 2020, 07:31:18 am
content: Hey folks!I recently purchased a 1986 Zenith ZFL-181-92 laptop off of EBay "fully tested and working". I just received it today, and while fully functional, it had a burning smell that was becoming more and more pungent by the minute. Being familiar with that smell from radio restoration, I immediately turned the system off and unplugged it. I opened the door to the back side of the computer where all the extra serial and parallel ports are located to see a tiny lick of smoke waft up from the inside of the case. From this, I thought it could be anything from a capacitor to a resistor to even the old battery pack.And so I began my exploration. I took many pictures documenting the placement of all cable and card hook ups so that reassembly will be easier later. I found one component of interest thatmaybe the culprit.This (resistor?) is marked with a broad, black bar with a delta-like symbol next to it. On it is printed C101M 67. There are several other just like it on the board. Component 1 (as seen in the picture) is of the same type, but without the white marks on top of it like component 2 (the one in question). None of the other components of the same type have these marks.One more piece of info. While this computer was smoking, it was fully booted up running a program. It was fully responsive with no observable electrical abnormalities manifesting themselves during its run time.I apologize for the length of this post, I just wanted to provide y'all with some good detail.

author: Prehistoricman
author_rank: Regular Contributor
timestamp: April 25, 2020, 01:07:53 pm
content: Those look like Matsushita resistor networks. It's probably a bussed network used to pull up a whole parallel bus.Do you know this is the component that is smoking? Why not power it up with the case open to make sure?

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 25, 2020, 01:14:50 pm
content: Check the tantalum capacitors first. They're infamous for overheating when they fail.

author: FRParker
author_rank: Newbie
timestamp: April 25, 2020, 02:54:56 pm
content: Turning on the computer while it was out of it's case was my original plan, but the design of it does not allow for observation of the board and running at the same time. The logic board, when the computer is not in pieces, sits with its chip-side facing up into the machine. The picture that I posted I had to fully invert so that it would be easy to view. The board also has several cables that prevent (due to their short length) any observation of the board when they are plugged into it. Finally, due to the fact that I'd have to set the computer on its bottom to turn it on, what little view I would have of the logic board would dissipate fully.I will just say the the #2 resistor I have labeled in that picture is the only one with those marks on top. The rest of the resistors have so sign of these white marks. I guess they could simply be wear marks, but either way, that was the first thing that caught my eye.I will certainly look at the tantalum capacitors next. I had to actually look up this style of capacitor because I didn't know what they looked like (I've never used them before). Now that I am armed with that knowledge, perhaps the scope of my vision will reveal something new to me. It was already smoking, so I'll look for distress and burn marks on those capacitors.Thanks for all the help thus far.

author: FRParker
author_rank: Newbie
timestamp: April 26, 2020, 07:20:26 am
content: A.S: All pictures are listed as mentioned (picture 1, picture 2, etc.)Alright folks, after some more picture taking and disassembly, I believe I may have found the source of the burning.I'll start off by saying that it was rather foolish of me to think that it was the resistor that was bad, considering that there were no burn marks or heat damage.After inspecting the board further, I found a couple of capacitors that, for a second, I thought were leaking. Upon further inspection however, it seemed that they were simply glued down so as to prevent shifting due to the long leads. Picture 1 is one of the capacitors in question on the logic board.I should have mentioned in my first post that the smell was extremely pungent when I came close to the speaker vent, circled in picture 2. When I opened the rear port cover, the smell was less intense there (though it allowed the smoke to escape) as opposed to the center of the computer.I was able to retrieve this module that rests under the PC speaker and in between the two floppy drives (picture 3). At first, I noticed this capacitor was a little close for comfort in regard to the resistor under it (picture 4),but it still lacked any obvious heat damage or swelling.I looked at the module a little longer and found a component that seems to have the beginnings of heat damage. In picture 5, I have circled the part in red. In pictures 6 and 7, I highlight what appears to be the beginnings of melting (plastic?). The component also smelled more "toasty" than anything else in that module, or in the computer. What's more is that it resides under the speaker vent (along with the rest of the module), which would explain why the burning smell was strongest there. There is no apparent collateral heat damage to surrounding components.If this is does pass muster as the source of the burning, what is this part? What does it do?If this is not the source, the next thing I will do is pull out the floppy drives and inspect them for heat damage.Thanks in advance!P.S: I should also mention that, assuming picture 1 simply shows a glued down capacitor, I have found no leaking capacitors. I have also found no swelling or capacitors that have burst due to pressure.

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 26, 2020, 09:05:33 am
content: The part in picture 1 is a crystal oscillator and no cap.From what I can see the transformer in picture 5 also seems to be OK from my eyes. That stuff parallel to the core looks like some glue or wax. But if the yellow tape that's around the coils shows some color changes to orange or brown then this might be your candidate. It is hard to tell if that's a shadow or a burning mark:Can you take a better picture to have a better view to the coil?

author: FRParker
author_rank: Newbie
timestamp: April 26, 2020, 09:20:18 am
content: It looks like there may be the beginning formations of an orange-ish hue to the plastic.

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 26, 2020, 09:44:26 am
content: No, that one looks OK. Looks like it was a shadow in the initial picture. Still it could be the troublemaker, but optically it looks so far very healthy. The beige stuff on the top is normal (glue or wax) and the reddish stuff on the yellow tape seems normal as well (I've seen is on other transformers as well). And the slight change of color on the top between the two text lines are due to aging.To your question what this thing is doing. It is part of the power supply that provides the different supply voltages or part of the battery-charger circuit. As it has a LC-Display it may need actually a reasonably high voltage for the backlight. Without having the schematics it is hard to tell which part of the supply is generated by this transformer. But it is most likely part of a smps (switching mode power supply).Just something came to my mind. Does the Laptop has a build in power supply (110V input). If yes can you look like these parts:RIFA Madness - Identifying RIFA Capacitors(the clear-yellow blocks). They might be located close to the Power supply connector. These are well known to fail in old devices. Especially ones that weren't used for longer time.

author: FRParker
author_rank: Newbie
timestamp: April 26, 2020, 09:50:24 am
content: No, this has an external power brick. It plugs into a one pin connector.Looks like I'll have to keep digging... I have no way of finding what's wrong with it until I find some type of physical sign. This computer is not testable when disassembled unfortunately.If this coil checks out, then it's on to the floppy drives.EDIT: It just occurred to me that when I first turned the screen on, I found that even on the highest brightness that the screen was rather dark. Based on pictures and written testimony from the seller, it was very bright while in his possession. This came all the way from Nova Scotia. Could it be possible that during transit the jostling caused a short in the coil? I know it seems far fetched, but it's worth begging the question. Either that, or this coil had not yet begun to fail while in his possession.I will say up front that I am aware that this is 36 year old screen technology. It's not going to perform as well as a modern LCD screen, but still, it was rather dim, dimmer than in the picture from its sale. I was also sitting in a comparable area of lighting in relation to the ambient brightness of the picture. I don't know if that is worth anything, but I thought I might say that as well.This is assuming that a failing coil would result in a dim screen. I believe it would be logical considering that drive A spun up (B was not in use at this time) and the computer fully booted and ran my demo disk program from Zenith.

author: calzap
author_rank: Frequent Contributor
timestamp: April 26, 2020, 03:08:03 pm
content: I remember when Zenith was one of the main makers of laptops and computer monitors. It was a very profitable business. But Zenith management couldn't imagine the company going away from making TVs ... something that had been the main business for a long while. The TV market was being taken over by Japanese companies. But HD TV was soon to be mandatory in the US, and Zenith thought they had an edge in development there. Problem was FCC kept delaying making HD mandatory at request of TV networks and stations. Zenith tried suing the Japanese companies for antitrust and dumping, and threw away millions in a losing legal case.So, to maintain the losing TV business (HD is almost here, and we'll dominate it!), they sold their profitable data systems business to Bull in France. I was stunned at the time ... it was such an obviously catastrophic decision. Soon, they were forced to sell part of the remaining business to LG in Korea. As things got worse, LG acquired the whole company. Today the relatively small Zenith division of LG manufactures nothing, but does DRM work.Mike in California

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 26, 2020, 03:48:32 pm
content: About the dim display. Until recently (couple of years before LEDs took over) cold-cathode-tubes (CCFL) where used for the backlight. So they are fragile but your picture show an evenly lit display so I don't think that a tube itself is damaged. If I'm not mistaken usually two are used. One on each side of the screen (left-right or top-bottom). Older display techniques might use more tubes, placed behind the screen area itself.And transformers are tough things. They don't break easily. They are just winded up insulated-copper wires on a plastic bobbin and in that case a ferrite core. And they don't create a burning smell unless you see that they start to melt the bobbin or leave visible marks on the yellow tape. I would not put any bet that the transformer is the cause.I oversaw that you mentioned the old battery pack. Was there a battery pack in there? I would put my money on that. Check the users manual if you can run the computer without them installed and see if that helps. The cells are probably beyond any good and could be shorted internally and overload the charging circuit or you'll generate some unpleasant chemical reactions.

author: FRParker
author_rank: Newbie
timestamp: April 26, 2020, 06:39:13 pm
content: Here's the battery pack. It's an old Sanyo NiCad pack. Considering there are other Sanyo parts in this computer and that NiCad batteries lost most of their consumer market share to other cheaper, less polluting options in the 90s (from what I've read), I'd say that this thing is between 25-30 years old. There are some low profile "bulges" along both the top and bottom of the pack, something that I initially assumed were just spots where the wires were fastened (either glued or soldered). Now looking at it, I'm not sure. In the last two pictures, I have circled seemingly abnormal bumps in green...... upon further inspection, I am almost sure this battery has burst. I can see corrosion and tan-ish battery material where the charging wire ingress. The manual says that the computer can be run without the battery pack for use as a desktop machine, so it looks as if I'll be sewing everything back together tonight after I finish some schoolwork and praying that it works.Would a Li-Ion with the same specs as this battery (12V, 1500 mAh) be a good replacement, or would it be incompatible with the charging circuit for some reason?Also, in response to your post Mike, it is a terrible shame what Zenith did to their computer wing. They should have held onto it and directed the funds of their legal battle with the Japanese into the company. They could have taken their screen technology and put it into their computer division. They were already bleeding money at the time like a sieve; there was no reason to burn the proverbial blood bags that would have kept the company alive. It's unfortunate, I would have loved to purchase a modern Zenith computer.

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 26, 2020, 07:01:51 pm
content: This red is terrible to take good pictures from. But I would agree that the battery is far beyond its lifetime. If you measure the voltage of the pack you will probably see an extremely low voltage if any. You should dispose it properly. Maybe cut the connector and keep it. As it might be a custom type to reuse it with a replacement pack.No, LiIon is probably not possible as it has other voltages and the charger in the computer is completely incompatible. NiMh might be a better choice. But even then the charger might not detect that the cells are full and overcharge them. I think that's the main reason why old NiCd chargers should not be used with NiMh cells.Probably you can get a NiMh pack build. Check your local model-plane or model race-car clubs if they can build one for you. The cells are not soldered but fused together. And use the battery only without external power supply to the laptop and charge the battery with an external charger for 12V and NiMh cells.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 26, 2020, 07:10:54 pm
content: Quote from: FRParker on April 26, 2020, 06:39:13 pmYes, but the charger will not work as-is. Hopefully there would be a simple way to modify it to turn off the charging current when the battery reaches 12.3V (4.1V/cell on a 3S pack) and have a BMS to handle protection and balancing. (A schematic of at least the power section would be useful.) Go bigger on the replacement battery since they're fairly cheap nowadays and the old hardware is not going to be particularly efficient. Hard to tell the exact size but it looks like a 3S2P 18650 pack will be about the same size as the old NiCd pack, so on the order of 4.4Ah or more.

author: FRParker
author_rank: Newbie
timestamp: April 26, 2020, 08:35:56 pm
content: The dimensions of the battery are 9'" x 1" x 2" (l x w x h when holding the battery vertically).I circled the burst points in sharpie. The outlines are almost the exact size and shape of the leakage. I say almost to account for any "shaky hand" error.For now, I'll just keep it as a desktop and come back to the battery issue another day.As it stands now, I'll be reassembling the computer tonight and testing it. The problem has been possibly id'ed as an old and burst NiCad battery pack that has shorted due to age and breakdown of the cells, resulting in an overload of the charging circuit (should it work tonight, I will edit this to show confirmation that it was the battery). The charging circuit is located on board the power module I pulled out of the computer that rests between the two floppy drives.I sure hope it works. I've kept an extensive pictorial log of everything I have unplugged, unscrewed, and unclipped, so there should be no investigative errors that interfere with the function of the computer. If it smokes again, I will be gobsmacked as to what it could be.Everyone who has replied to this post has been indispensable and most helpful during my journey with this computer. Your dedication to this thread and in-depth replies are all deeply appreciated. You have my sincerest gratitude. Thank you all. I will report back to this thread with my results either tonight or tomorrow.

author: FRParker
author_rank: Newbie
timestamp: April 27, 2020, 10:20:03 am
content: After reassembling the computer and powering it on, it functions perfectly. The battery was the culprit. This has probably been the biggest lesson in Occam's Razor for me to date. Thank you all again for aiding me in this journey.

author: wallacedg
author_rank: Newbie
timestamp: November 24, 2020, 05:27:42 pm
content: found this a little late....I have one of these beasts - fully functional, complete with DOS 3.2 and PE (word processor) disks. It was my first laptop (if you can call these things laptops). You can HAVE this thing if you want it, just pay half of shipping costs.Davis

author: VE7XMC
author_rank: Newbie
timestamp: December 24, 2020, 11:54:56 pm
content: Quote from: FRParker on April 27, 2020, 10:20:03 amThanks for this thread!I just picked up a ZFL-181-92 for restoration.I'll be sure to correct this before I power it on.I plan to use mine as an educational display (for DOS and a serial terminal for ham radio modems, my PiDP-8 and PiDP-11).I'm looking for any floppy images for this laptop if you have them!