Lambda LP_412_A_FM PSU and MC1466L - Page 1
Forum section: electronics / repair

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: July 21, 2018, 05:35:41 pm
content: Hi Everybody,I am trying to repair a Lambda LP_412_A_FM PSU ( 0-40 V 0.9 A).The problem on this PSU is the current limit. It cannot go beyond 0.2 A ( instead of 0.9).I verified the R101 resistor and R102 10k pot (see schematics attached). There are both OK.Then I put the current pot to max ( 0.2 A in my case) and try to change the R102 10k pot. This had no effect.So I suspect that the main IC (FBT-00-034 in the schematics, but FBT-031 in the actual board) isdamaged.Could you confirm this ?From the web, I understand that a possible replacement is MC1466L which seems to be available in cerdip package on ebay.Does anybody has experience of buying recently a MC1466L on ebay ?Thanks for all.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 21, 2018, 06:08:58 pm
content: The output current sensing is done between pins 11 and 3 of the ic, the ic is used in a floating regulator topologyFor Ebay not sure they are genuinetake a chance ... and try it, they are no longer available for a looooong timeMy self i'm trying to buy few of them, waiting for an answer ...you have a very good site explaining things :http://chemelec.com/Projects/MC1466/MC1466.htm

author: borghese
author_rank: Regular Contributor
timestamp: July 21, 2018, 07:03:33 pm
content: I would also check the value of R103, the current sense resistor.

author: Relayer
author_rank: Contributor
timestamp: July 21, 2018, 11:47:27 pm
content: Hello AlcidePiR2,I would try checking the indicated voltages around IC101 under load conditionsas well as unloaded. See if any of them are correct.The voltage of 11.1V shown above the IC and next to where its written:"MAX. OUTPUT CURRENT CALIBRATION CONTROL".Measure it while adjusting R102 to see if there's any wild variations.Might pay you to mark the pot prior to adjustment, just in case you need toreturn it to its original setting.Regards,Relayer

author: pastro50
author_rank: Newbie
timestamp: January 26, 2024, 10:08:13 pm
content: I have the exact same issue on my supply. Did you have any luck fixing this?I'm going to try shorting out the current sense and see if that kicks up the current at all.

author: exe
author_rank: Unknown
timestamp: January 26, 2024, 10:19:28 pm
content: I think I've seen someone made a discrete replacement for it, try to google it. First link I found:https://www.eevblog.com/forum/repair/making-replacement-for-mc1466l/From there:https://tubetime.us/index.php/2014/09/28/a-miniaturized-discrete-mc1466/

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 26, 2024, 11:25:34 pm
content: I ended up redesigning the board for my Lambda 722. Used the same output chain of transistors.I do not think it is as stable, it jumps around a few millivolts and is sensitive to temp. But it works.I do have the schematic that I came up with, uses three op amps and two one K big multi turn pots.The lack of an embedded Zener is a drawback in my design.

author: Jwillis
author_rank: Super Contributor
timestamp: January 27, 2024, 09:29:20 pm
content: There are still MC1466L new old stock around but get more expensive year by year. The alternative is the MC1566L which is pin identical but has some minor operating differences.MC1466l/MC1566LAnother alternative is here.https://hackaday.com/2017/12/31/making-a-classic-chip-from-discretes/and the PCB can be bought herehttps://oshpark.com/shared_projects/tU1Dv8o4Be patient with OSHPARK as it may take as much as a month to receive your boards. I got a few myself but haven't got around using them.

author: pastro50
author_rank: Newbie
timestamp: January 29, 2024, 08:09:25 pm
content: It is hard to find the replacement parts and not buy a fake part it would seem. I didn't see any at least on Ebay that didn't come out of China and that could be iffy in my mind.Have you had any luck buying parts?

author: Jwillis
author_rank: Super Contributor
timestamp: January 30, 2024, 01:46:40 am
content: Quote from: pastro50 on January 29, 2024, 08:09:25 pmIt can be a crap shoot. I guess I've been pretty lucky ( I should by a lottery ticket). I don't go to Ebay much anymore because they've become to much of a pain to deal with. Most components I get from Ali have been Ok and haven't given me any problems. But I don't jump on the first lowest price. Check How long a vendor has been in operation and rating. If you still have questions, talk to them. If they get ignorant and vague drop them and move on. There are good vendors in China, you just have to do your research.

author: pastro50
author_rank: Newbie
timestamp: February 01, 2024, 04:38:49 am
content: That's fair. I'll give it a shot.