When doing repairs, do you upgrade the broken parts - Page 1
Forum section: electronics / repair

author: nukie
author_rank: Frequent Contributor
timestamp: April 04, 2012, 03:08:18 am
content: From your personal experience. When doing repairs to electronic devices/equipment replacing parts such as capacitors, transistors opamps. You want the repair to last. Do you replace them with quality parts or just cheap generic parts?I often go extra miles regardless whether it is a job or my own equipment. For capacitors I would look for better temperature and longer life, 1% resistors, brand name transistors and diodes. I often wonder if this a mental disorder or is it really worth it? What is the outcome if I have used cheaper parts, anyway the broken device is built with cheap parts. Are you tempted to 'upgrade' parts which are likely to fail. It's common to find consumer electronics filled with junk parts these days.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 04, 2012, 03:37:54 am
content: Quote from: nukie on April 04, 2012, 03:08:18 am1% resistors are pretty much as waste of time,unless the original manufacturer specifies them for some reason.If the device is older,some of the newer components have higher specs,so,(if they aren't fakes!)they are worthwhile using.I would definitely use higher spec Electrolytics,as many of the OEM ones are crap!I have also made a habit of replacing very low capacitance Electros with Monolithic Ceramics.There is a lot of nonsense spoken about "The Engineer used it for a reason!".Most of the time 1uF & 0.47 uF Electros are used,because they are there,& cheap!Quite often,manufacturers( & not always "one Hung Low"),"sail close to the wind" with resistor wattages,use tiny tracks in power circuits,& other dodgy practices.If other companies produce very similar equipment using better spec'd components,it makes sense to upgrade "El Cruddo's" parts to that level.

author: sonicj
author_rank: Frequent Contributor
timestamp: April 04, 2012, 03:43:39 am
content: i usually stick in whatever i have "in stock" or dig for a suitable replacement in my junk box. if i have to order a part, i spend a few cents extra on something decent.-sj

author: ampdoctor
author_rank: Frequent Contributor
timestamp: April 04, 2012, 04:04:40 am
content: if it's older equipment, then usually any part you replace will be of better quality than what came out with very few exceptions. My entire stock is pretty much all 1% metal film resistors, np0 ceramics and mica, and poly caps. But if I'm stuck ordering a part that's not stocked, I usually upgrade as long as the cost isn't prohibitive. If it's things like caps or resistors, we're usually only talking about a few cents difference so why not go the extra mile.

author: david77
author_rank: Frequent Contributor
timestamp: April 04, 2012, 07:21:18 am
content: I usually stick in whatever I've got in stock if it's reasonable to do so. If I need to order some part in I usually choose one with the same or higher specs.I'm not too fussy about it, though. As long as it works it's fine.Just in the last week I had to replace an unobtanium opamp in a DMM's RMS converter, the replacement part does work but I had to tweak a few resistors to get it to specs. Took me a couple of hours to get it right, basically guessing what to change.

author: T4P
author_rank: Super Contributor
timestamp: April 04, 2012, 07:40:24 am
content: I don't tend to overspec , but if it improves performance by a huge margin i will .There's no point overspec-ing if the stock longevity is already 10 years .

author: Rerouter
author_rank: Super Contributor
timestamp: April 04, 2012, 08:54:12 am
content: like most of the others, it depends on what it is, if itcosts $50 but is worth alot to me personally i will likely go and overhaul the thing with far better components so the thing will outlast me, but at the same time if something is worth $$$ but i rarely use the thing i will generally just replace what had broken with a better spec part and look into any near failures but not actually dig too deep,the other irony is the older something is, the more i care about it, if its the latest and greatest, i normally cant see half the magic behind it, so barely look into it, but older gear tend to get to the point that i go and try and work out some of the more interesting sections,

author: Unknown
author_rank: Unknown
timestamp: April 04, 2012, 09:07:04 am
content: 'Upgrading' parts should be done with care. Power supplies might become unstable if the ESR of the output caps is much lower than original. Replacing ancient NE5533s with modern opamps may also degrade performance if the design engineer did his job and optimized the design for the NE5533, like in some audio analyzers.Replacing electrolytic caps with crappy ceramics may or may not be an improvement, depending on the design. ESR will be lower (this can be good or bad, many LDO regulators are not stable with ceramic output caps). Decreasing ESR increases the Q of a system, not very desirable if it's prone to oscillation. Capacitance may be lower with a high DC bias.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 04, 2012, 09:58:22 am
content: Quote from: alm on April 04, 2012, 09:07:04 amMonolithics are hardly crappy!Small value Electros drop radically in capacitance,anyway,so even with any small difference due to a ( Hardly high!) DC bias, Monos will still be better!If the circuit is prone to oscillation,it is poorly designed in the first place!Most places where small electros are used are not extremely critical,anyway,but the monos do not lose capacitance like old small value Electros.I have done this type of replacement for many years.Originally it was by necessity,as new Electros are rarely the tiny ones used by OEMs & don't fit,& I've had bad experiences with Tants.The Monos have done the job with consistently good reliability in all cases.In power supplies,if the original caps have cooked,& every other comparable supply uses lower ESR caps,I would take the chance oninstability,compared with the certainty of cooking high ESR caps.

author: Unknown
author_rank: Unknown
timestamp: April 04, 2012, 10:36:59 am
content: Quote from: vk6zgo on April 04, 2012, 09:58:22 amThe quality of the ceramic caps depends on the dielectric. Some high K materials are definitely crappy in the presence of DC bias.Y5Vmay lose > 80% of it's capacitance at 50% of its rated DC voltage. This is for MLCC, but I don't see why monolithics with the same dielectric would be any better.

author: T4P
author_rank: Super Contributor
timestamp: April 04, 2012, 11:08:48 am
content: Yep , Y5V should be avoided generally .I use either X5R for the high values , X7R for the mid values and NP0 for the low values .I just want to avoid running into problems with Y5V .

author: rsjsouza
author_rank: Super Contributor
timestamp: April 04, 2012, 11:09:40 am
content: I usually try to not overspec, but instead I try to get reputable brands to replace (not an easy task if you are talking about getting one from the local store).Apart from that, I've seen the manufacturer skimp on specs: the power supply of the control board of my fridge had problems caused by two underspec'd filter electrolytics (the TOP246-based switching power supply required 35V caps, but GE decided to use 25V instead).I've also found some cutting corners on heat disspation: my 10 year-old receiver (Teac AG-D9320) had a blackened PCB area where a TIP31 was. I adapted a small heatsink to its back to avoid future issues. My subwoofer (JBL SCS300) was also refusing to turn on at a times, and the PCB around the power supply transistors (a complementary pair of TIP31/32) was heavily blackened. I adapted a huge heatsink to the back of both and had to tie it to the external aluminum housing (there are no vents in this equipment).Another thing I usually do is re-solder all the high-power connections. The receiver I mentioned above had a cold solder joint that caused a 7805 to get disconnected after 10 years. I then re-soldered all power devices to avoid trouble in the future (regulators, power transistors, power resistors, etc.)

author: vk6zgo
author_rank: Super Contributor
timestamp: April 04, 2012, 11:25:58 am
content: I have not seen any such effect .The really tiny electros are usually used in places where you would normally use polyesters or similar,but don't have enough room to fit them in.I don't know what dielectric is used in common monos,but it would be interesting to test themThe very small electrosdolose a similar proportion of their capacitance due to aging,&,as in many cases the circuit is still working correctly,& the caps were replaced after testing, the circuit design seems to tolerate this.The good design may be masking the problem,& I may be kidding myself!

author: FenderBender
author_rank: Super Contributor
timestamp: April 05, 2012, 01:42:40 am
content: I mean most passive components and semiconductor parts are quite reliable naturally. Really the only thing I'd look at when making a repair is, as everyone has said, electrolytic caps since they do have a wet electrolyte that are prone to all sorts of problems.But I'd go with the attitude of, "If it aint broke, don't fix it". The only time I'd fix it is if you KNOW that it will die and that it's going to be a catastrophe if it does. Like some older wet tantalums are good examples of this, and they are pretty common in some older test gear. A lot of these tantalums die shorted which can be very bad. So in that case I'd fix it before it actually dies.And if you are going to make a repair, don't replace the part with crap...That's not much of a repair. Especially with electrolytics. Some other parts, you might be able to get away with a cheapie..meh, electros, try to use some good quality Japanese brand or maybe Taiwanese...or hell American!