Not completely lost...just need a little help.  (Diodes) - Page 1
Forum section: electronics / beginners

author: Mace_Hacker
author_rank: Contributor
timestamp: March 01, 2021, 05:11:11 pm
content: I am working on a solid state, transistor controlled, ignition module for my 1982 Yamaha Virago XV750 motorcycle.Yes I know this is not a tube radio however, the same trouble shooting process applies to this board and it's components.I am recapping the entire board and replacing the main transistors, the IC's, a few 2sc1815's, and a few 2sa628's. I am hoping that I can leave all the resistors alone.What I am struggling with is the diodes. I am not an electronic tech. More like a bench monkey. Tell me what to replace and I can do that...diagnostics is what I am just getting into. I have pictures and some readings on a few of the diodes. I need to know how to determine the correct value of each one so I can replace them all as well.A little guidance on where to post questions for help on this would be great.Thanks,Mace

author: RoGeorge
author_rank: Super Contributor
timestamp: March 01, 2021, 05:28:40 pm
content: "Recapping" (replacing the capacitors) means to change only the capacitors, mostly the electrolytic ones, because with time they bulge or dry out and become damaged. Recapping is common mostly for consumer electronics of at least a few years old. However, for automotive electronics the recapping is usually not necessary. Automotive electronics boards are designed with more care, and more expensive parts than consumer electronics.Anyway, recapping does not mean ALL the components need to be replaced. Other parts does not "wear out". Transistors, integrated circuits, diodes, resistors, etc. works correctly forever. Their mileage is theoretically infinite, change them only if something is fried out.Why do you want to change all the components, what are you trying to achieve?

author: Mace_Hacker
author_rank: Contributor
timestamp: March 01, 2021, 08:48:50 pm
content: The board is 40 years old and, defective. Now, I understand that automotive parts might be more robust than consumer grade but, 40 years is 40 years. Something has been damaged on the board causing it to fail. Most likely the bike was jumped incorrectly and something got fried.As I said though...I am only asking for help in sorting out the diodes. The other components I am replacing I am good with.Yes, theoretically some of them might be fine but it's just as fast to replace them than test.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 01, 2021, 09:09:14 pm
content: I would replace just the capacitors, then expect it to work. If not, measure with a DMM the power transistors and power diodes at first. If those are also good, measure the remaining low power transistors/diodes.Anyway, about diodes, they are marked in many ways, some are written in clear text, some have colored lines or dots, etc. It depends of the size and technology of the diode. If the original model was discontinued, search for the diode model crossreference, to find a replacement. If there is none, search for the diode's model number and the word datasheet.There are many, many types and models. Put some clear photos with the board (both sides), and some close-up photos of the diodes you want to replace. Put the schematic diagram of the board, too, if you have it.Without crisp photos or the right schematic for your board, there's no way to guess what diodes you are seeing there.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 01, 2021, 09:32:15 pm
content: Most diodes and also many transistors tend to fail with a short. So one can do a first set of tests with parts still in the board. It the DMM reads a short the part is highly suspect (could still be another semiconductor in parallel).

author: Mace_Hacker
author_rank: Contributor
timestamp: March 01, 2021, 11:17:40 pm
content: No schematics to be found for this. I looked.I tested diodes in circuit and then took 3 out to test them. You can see the results on attached picture...out of circuit is in yellow.I also tested the removed diodes with my cheap LCR, component tester.Results are as follows:D01 - 640mv C=60pFD02 - 762mv C=285pFD03 - 695mv C=2pFI know many of you guys have been doing this for years...I have not. I know basics...barely. It's far easier for me to just replace some things than test them.Mouser has all the caps I need and I found reliable sources for the IC's.Newer transistors for the mains will be used....better specs.I plan to test voltage drop on Diodes tomorrow. We will see how that goes.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 02, 2021, 01:02:09 am
content: All 3 diodes tested looks good (if you desoldered at least 1 leg of the diode before testing).Anything between 0.5V ... 0.8V on the LCR meter would be OK. The exact value doesn't matter as long as it is identified as a diode by the LCR meter. Just desolder one pin of each diode before measuring, measure the diode with the tester, and if it's good solder the pin back. If you don't desolder one pin, with the component in the circuit the measurement might be misleading. Desolder at least one pin of the diode to be sure you measure only the diode, and not the whole board.The small glass diodes looks like 1N4148. My bet is they are all good, too. The slightly thicker glass one is probably a Zener diode, usually the model is printed around the glass.Again, if the diodes test good, just solder them back to the board. They do not wear out, like tubes. They either work, or are failed as a short circuit or as an open circuit. Polarity matters, so if you remove them completely take care to solder them back with the painted ring on the same side as it was initially.

author: perieanuo
author_rank: Frequent Contributor
timestamp: March 02, 2021, 10:07:59 am
content: D02 is unclear to me, you said of the circuit is O.L/O.L but you wrote 0.7 V or somethingwhich one is the good value?seems to me like a zener diode, the big one with yellow trace towards herO.L is what, open circuit?

author: RoGeorge
author_rank: Super Contributor
timestamp: March 02, 2021, 11:45:42 am
content: Quote from: Mace_Hacker on March 01, 2021, 11:17:40 pmSince the diode D02 has 0.7V when disconnected, it means the diode is working properly. What you measure when the diode is soldered in the circuit may be a lie, because the rest of the circuit alters what you measure.Whatever a diode measures when it is soldered is not enough to decide if that diode (ar any other component soldered in a circuit) is good or not. Desolder the diode, or at least lift one terminal from the board, so the circuit between the diode and the rest of the board is interrupted while measuring.Again and for the last time: the plan to replace everything is a bad idea.Try to replace at first only the electrolytic capacitors, the ones looking like small cylinder cans, I see 11 of them in the pics. Then try if it works. If still not working, remove the power transistors and test them with your RLC universal tester. If the tester identifies them as transistors, just solder them back. Do not replace them with newer and "better" equivalent transistors.In case you do not trust the universal tester, a DMM set on diodes mode can measure transistors, too, like this:https://instrumentationtools.com/testing-a-transistor-with-a-digital-multimeter/

author: Mace_Hacker
author_rank: Contributor
timestamp: March 02, 2021, 02:57:02 pm
content: D02 - When tested with multi-meter,out of circuit,reads OL/OL (out of limit) in either direction and hadno continuity.When it was tested in the LCR it did show (D02 - 762mv C=285pF) so I don't know.I will test each diode by removing one leg to take it out of circuit.I will also check it with the LCR and post results.Moving forward, the plan will be to test each diode and only remove one if it determined to be "bad".I would still like to know what each Diode is and it's value. That said, will my testing with just the multimeter and LCR be enough information do do this or will I need to also measure voltage drop on each one as well? I figure more information on each one can't hurt.The capacitors however, will all be replaced for good measure. Several tested were not in spec and the ceramic ones; almost all are cracked or cracking.This module's placement location, during normal operation, is under the petrol tank; secured to the frame; directly over the engine. The engine is air cooled and there is a lot of heat build up where this module sits. 40 years of heat and vibration adds up.I know you are against replacing things that work...like the transistors but, the newer ones that I am going to use are actually a very good improvement to the operation of this module. BU941ZT allows to switch higher currents (should result in more longevity) and b) it has got a marginally different (I think quicker) switching behavior.In any case these are used in ignition modules regularly so using them in this will be fine.The only components left on the board that I was not planing to test were the resistors...and the IC's.Here I was going to "assume" the resistors were still good....and the IC's I was going to replace. (I have no way to test them...or at least I don't know how to at this time. They are simple switching components and do not need any special programing. I can get them cheaply and just figured it would be safer to replace them)If.......there is way to test them and keep them if they are good....fine.....let them stay.If I haven't said it before, Thank you all.I do appreciate the help and guidance.Cheers,Mace

author: CaptDon
author_rank: Super Contributor
timestamp: March 02, 2021, 04:30:19 pm
content: I nearly bought a Virago 750 but it was a slug compared to my Suzuki GS750 and they wouldn't give me shit for a trade-in. Isn't the distributor mounted low and on the front center of the Virago where it is prone to water damage? By the way, remove all of that dark yellow plyobond glue around everything. It becomes conductive as it ages and messes thing up.

author: Mace_Hacker
author_rank: Contributor
timestamp: March 02, 2021, 05:01:30 pm
content: "CaptDon", the 'coils' are mounted in front, above engine. Originally there were 2 separate ones but, removed them and went with a single coil.You are right about it not having a lot of power. It is torquey but, odometer only goes to 80mph. Good around town bike; not made for long road trips.I will make sure to finish removing the glue from board. I didn't know it could be conductive but, removing it was in the plans anyway.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 02, 2021, 07:27:42 pm
content: Nice bike!Quote from: Mace_Hacker on March 02, 2021, 02:57:02 pmIf D02 shows OL in both directions when disconnected (and from now on we should never talk about in circuit measurements, so to avoid any future confusions), and with the DMM instrument set to measure diodes, then the diode it's certainly broken (interrupted), no matter what the other LCR instrument measures.By the way, what LCR meter do you have? Is it something like this one here,https://www.aliexpress.com/item/32740546292.htmlthat can autodetect the components and draw the symbol on its display, or some other model of LCR?

author: Mace_Hacker
author_rank: Contributor
timestamp: March 03, 2021, 01:44:49 am
content: RoGeorge, I understand. I will only refer to the diodes tested as, o.o.c.Tonight I did a quick voltage drop test of the three that I have out so far.Results are below.Test voltage source - AC/DC adapter - 15.12 v @ 400 ma1 k resistor in line on positive lead.MeasurmentsD01 - .7 vD02 - 5.53 vD03 - 15.1 v

author: Mace_Hacker
author_rank: Contributor
timestamp: March 03, 2021, 03:33:07 am
content: I didn't want to clutter up the forum with a bunch of pictures so I put them on my imgur page.(https://imgur.com/user/MaceHacker/posts)I wanted to show a few things to give an idea of what I have and am working with.My tools, some parts, some projects.If you look at the following galleries you can see what I am talking about.Some of my electronic tools; Electronic parts and stuff; My projects;and if anyone needs to see more pictures of the TCI I am repairing it's on there too -- 1982 Yamaha Virago XV750 "TCI"I have a lot of parts and stuff I got from a retired Electrical Engineer the retired from Southern Bell (Telecom company) He was also a member of MENSA and built/operated ham radios. I wish I had met him years ago. Unfortunately I met him after he developed Parkinson's and did not have long to live. He left me a good bit of useful things though.Again, thanks to all.Mace

author: RoGeorge
author_rank: Super Contributor
timestamp: March 03, 2021, 08:28:16 am
content: For that setup with a 15V DC source and a series resistor, two voltage measurements are needed for each diode, first in one direction, then with the diode reversed, in the other direction:- normal diodes will show a voltage drop of 0.7V in one direction, and 15V when connected in reverse 0.7V/15V- a 5.1V Zener diode will show 0.7V one way and 5...6V when connected in reverse 0.7V/5V- a shorted (broken) diode will show a very low voltage (about 0V or so) connected either way 0V/0V- an interrupted (broken) diode will show 15V conected either both ways 15V/15VWith only one voltage is hard to guess. For example- D02 can be a good 5V Zener if it measures 5V one way and 0.7V the other way, but defective if it shows 5V/5V. One direction has to be 0.7V no matter the diode type.- D01 can be a short circuited diode if it shows 0.7V/0.7V, but a good one if it's 0.7V/15V- D03 can be a good diode if it shows 15V/0.7V, but interrupted if it measures 15V/15V

author: perieanuo
author_rank: Frequent Contributor
timestamp: March 03, 2021, 08:40:59 am
content: Quote from: RoGeorge on March 03, 2021, 08:28:16 amyep, d02 is deeeead, told youyou can test like rogeorge said, put like 20-30V with series resistor calculated for aprox 5-10mA (you can put 1k, for 30V and 5V zener you got 25mA, that's fine, the diode wattage is big) and you find the naked truthd02 can be also 15V like protection from commutation spikes in auto, so put more minimum 20V on d02+resistor (in series) for polarise the thingor just measure it 'in circuit' with your module attached to the bike/battery

author: bobbydazzler
author_rank: Regular Contributor
timestamp: March 03, 2021, 10:23:09 am
content: I thought carbon resistors could stray in value over time and high temp? I'm not sure what temps this has been subjected to but the board would probably get hottest right after you turn off the bike - heat from motor has no moving air to remove heat and it soaks up into the board?

author: Mace_Hacker
author_rank: Contributor
timestamp: March 03, 2021, 12:59:30 pm
content: bobbydazzler, I haven't messed with the resistors yet....hoping they will be fine but, yes, it's 'possible' that some of them could be out of tolerance. As for the heat the part is subjected to...you are probably right again. Just after engine shut off the heat would rise and collect there but, in summer months it would still get a lot of heat there regardless. (Which is when it gets ridden most.)

author: Mace_Hacker
author_rank: Contributor
timestamp: March 03, 2021, 01:02:37 pm
content: perieanuo, yes. I think so too. I will use higher voltage for more testing.RoGeorge, gotcha. reverse leads; measure again.

author: Mace_Hacker
author_rank: Contributor
timestamp: March 03, 2021, 06:13:46 pm
content: Here are my latest test results. I hope this is enough information. It also shows how I set up my test.EDIT: The AC/DC adapters I used for testing were both 400ma if I remember right. I only used the one 1k resistor in line for both tests. If this was wrong then I need to set it up and repeat tests.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 03, 2021, 08:18:16 pm
content: - The measurements made with the 15V adapter show all diodes were good.- The measurements made with the 40V looks like D02 and D03 are now damaged, or maybe something else went wrong with the 40V setup.Do not test them at higher voltage. Higher voltage will not get you "better" testing. Higher voltage at most will just broke perfectly good diodes. Let's hope it was just a problem with the wiring, or with the 40V power supply, and the diodes were not damaged in the process.Try again. Test at 15V only. Do not repeat the tests at 40V."Better" is the worst enemy of just right.About the DMM indication on(ohms), that is for measuring resistors. Trying to measure diodes with the DMM set onis irrelevant, that is why the DMM has a measuring mode made specially for diode testing. Rotate the selector in the position for ohms/continuity/diodes, then press repeatedly the SEL button until a diode symbol appears on the display. Do not apply any external voltage, and just connect the diode to the DMM, first in one way then in reverse. When it is set on diode, the DMM will generate its own voltage for the diode. For a good diode, in one way the DMM should say about 0.7V, and when the diode is reversed the DMM should display OL.Same as described in the instrument manual, see the "Diode Testing" sectionhttps://images.carid.com/performance-tool/items/pdf/w2971-owners-manual.pdf

author: Mace_Hacker
author_rank: Contributor
timestamp: March 03, 2021, 10:22:50 pm
content: Re-Tested at 15v and there was no noticeable difference.This is my cheap DMM in action. I can not set it to just the "Diode" mode. When I do it displays numbers and does nothing when you try to measure anything. IF you just turn it to the OHM position it has an 'auto' mode. That does work when I try to measure the diodes.See link below.https://youtu.be/1VduR313Glk

author: RoGeorge
author_rank: Super Contributor
timestamp: March 03, 2021, 10:43:53 pm
content: Quote from: Mace_Hacker on March 03, 2021, 10:22:50 pmGreat, all 3 diodes are good.About the DMM, something is wrong with it. The instrument's manual says the diodes are tested with "Open circuit voltage: about 1.5V", so without anything connected while in the diode mode the DMM should display about 1.5V, while yours display 0.794V.(A DMM does internally about the same trick you did while testing with the 15V and the series resistor, just that the DMM is using a lower voltage for the diode mode, yours should use 1.5V according to the specs, not sure why it displays only 0.794V).The AUTO mode is for resistors measuring, it means the instrument will select the appropriate range for resistor, so the number will fit on the display no matter how big or how small is the value of the measured resistor.There is no AUTO mode for diodes in DMMs.

author: Mace_Hacker
author_rank: Contributor
timestamp: March 03, 2021, 11:10:52 pm
content: Just to be safe. I will purchase a better DMM and confirm. I am dubious of D02 but, you may be right.I need a better DMM anyway so it can't hurt!

author: perieanuo
author_rank: Frequent Contributor
timestamp: March 04, 2021, 08:55:16 am
content: your dmm is no good, maybe powered with aa/aaa batteries, the diode tester is off the chartusually all zeners sustain 30V which I recommended with no problemfor example, first one from farnell says:"BZV85-C27,113Working voltage range:nominal 3.3 V to 75 V (E24 range)"if we are paranoiacs we limit at 20-25V, but if you got 27V zener it will never polarise, only in forward mode you will see approx 0.7Vif you gonna repair you need a correct diode tester, it's a must have

author: perieanuo
author_rank: Frequent Contributor
timestamp: March 04, 2021, 09:01:37 am
content: Quote from: RoGeorge on March 03, 2021, 10:43:53 pmthe diode mode in dmm's is some kind of automatic by default, you got the forward polarisation voltage for the tested patient, for zeners in reverse you don't get the correct voltage normally (you haven't enough voltage to reach the threshold in reverse polarisation cause you're applying only small voltage, in your case 1.5V)BUT if forward voltage is ok for that zener (for example, like 0.7V), the reverse will be good too, haven't see a single zener good in forward and bad in reverseseems all your 3 diodes are fine, retest with 15V/1K series and move forward

author: RoGeorge
author_rank: Super Contributor
timestamp: March 04, 2021, 09:05:35 am
content: Quote from: Mace_Hacker on March 03, 2021, 11:10:52 pmMaybe the DMM just needs new batteries, but one can never have enough DMMs, welcome to the club.However, D02 looks exactly like a Zener diode, and measures like a Zener. No doubt about it, and no need to worry about that one.That's a working 5 volts Zener diode.https://www.vishay.com/docs/85607/bzx85.pdf

author: perieanuo
author_rank: Frequent Contributor
timestamp: March 04, 2021, 11:59:24 am
content: Quote from: RoGeorge on March 03, 2021, 08:18:16 pmBZX85C5V1: if you put 40V with 1K resistor with this diode, you got 40-5=35, 35V/1k==35mA.The pdf test that diode at 45 mA and fig 8 will point breakdown won't happen even with 40V on it.which confirmed by the tests done by OPso the diode can't be damaged if tested like this

author: RoGeorge
author_rank: Super Contributor
timestamp: March 04, 2021, 01:00:38 pm
content: Sure, except all the assumptions before drawing the conclusion that "the diode can't be damaged if tested like this" might have not been true. For example, can you bet your head on that resistor being indeed 1k, as it was drawn, and able to dissipate 1.5W? I wouldn't, but we are nitpicking already.Also, there is no auto mode in a DMM diode testing mode. No diode "range" is switched automatically depending on a measured diode, like the voltage range is switched automatically depending on the measured voltage, or like the resistance range is switched automatically according to the measured resistor.Since the diodes probing was sorted out, any further details will just add confusion.Have a nice ride with that bike!

author: archil
author_rank: Contributor
timestamp: March 04, 2021, 02:08:10 pm
content: can you show us photos of board ?

author: Mace_Hacker
author_rank: Contributor
timestamp: March 04, 2021, 04:31:03 pm
content: To help resolve any problems moving forward...this is the new DMM I ordered and will have by tomorrow;AstroAI Digital Multimeter, TRMS 6000 Counts Volt MeterI am looking forward to using it. I did some research on it and for the money it is a good value. It should do everything I need it to do.Again, I do appreciate all the input!

author: Mace_Hacker
author_rank: Contributor
timestamp: March 05, 2021, 06:06:52 pm
content: Quote from: archil on March 04, 2021, 02:08:10 pmarchil, if you look back on page one of this thread there are picture and in one of my posts there is a link to more photos.

author: james_s
author_rank: Super Contributor
timestamp: March 05, 2021, 06:15:26 pm
content: The age of the transistors and ICs is irrelevant, they don't wear out unless something damages them. You are more likely to cause a problem by needlessly replacing components than prevent one. There are also numerous cases where a modern component does not have quite the same characteristics as a vintage one of the same type number and may not work in certain circuits.

author: Mace_Hacker
author_rank: Contributor
timestamp: March 22, 2021, 01:45:03 pm
content: Update:I have replaced my multi-meterwith a (AstroAI Digital Multimeter, TRMS 6000 Counts Volt Meter) and re-tested the diodes. They do in fact appear to be fine. (Remarkable what using the right tools can achieve.)I ordered all new capacitors, mostly from Mouser, and I am still waiting on them to arrive. I did order 2 capacitors on Amazon, twice; because I did not like the way they looked. Too small, in my opinion. (see picture)Lacking a better alternative I will probably use the first and last ones shown in the picture.When the rest of my parts show up I will swap them out, test, and update post again.Thanks again!Edit:I just ordered 2 different capacitors from Newark to compare to the ones I got from Amazon.We will see.

author: james_s
author_rank: Super Contributor
timestamp: March 22, 2021, 05:04:48 pm
content: Modern capacitors are typically much smaller physically than older parts, you should not judge a capacitor by appearance. I would never order electronic components from Amazon, what you get is likely to be the cheapest generic Chinese junk available and a total crapshoot.That said, in 30+ years of tinkering and repair I have *never* seen a ceramic capacitor fail except when it had been physically broken. I would absolutely leave the original in place unless you have good reason to suspect it is defective.

author: bobbydazzler
author_rank: Regular Contributor
timestamp: March 22, 2021, 06:02:36 pm
content: Ceramic caps usually fail short circuit you could test them for that if you don't want to change them, and I think you can still get the big disk ceramic caps pretty easy.

author: Mace_Hacker
author_rank: Contributor
timestamp: March 22, 2021, 06:27:13 pm
content: Several of them are cracked, dry, brittle. 40 years of heat an vibration. I know, most of the time they should be fine but these aren't.The original ones were only rated for about 15 years to begin with so, I think they have done ok.The diodes, resistors and, transistors I think, will be just fine. Like you said; these usually are ok as well.

author: Mace_Hacker
author_rank: Contributor
timestamp: April 08, 2021, 07:03:42 pm
content: This was why I opted to replace all the ceramic capacitors, as well as all of the other capacitors.They were so brittle that they crumbled with little effort.Everything is done now. I just need to reattach the wires, add some schmoo, and seal her up.Fingers crossed.

author: josh132
author_rank: Contributor
timestamp: April 08, 2021, 07:13:38 pm
content: diodes aren't likely to fail. What i would replace is capacitors and resistors and they can decay over time. Transistors can fail but also unlikely.