***Gone*** Free for local L.A. pickup - Lambda LQD-422 ***Gone*** - Page 1
Forum section: electronics / general

author: ruairi
author_rank: Frequent Contributor
timestamp: June 23, 2017, 04:19:47 am
content: ***Gone***Hi all,I bought this Lambda on eBay maybe 6 years ago and paid more than I should have. It was faulty on arrival. The right channel outputs voltage correctly but the left is stuck at around -0.5V regardless of voltage setting. The voltage and current readings on both channels wander randomly.I have the device manual in PDF and this is likely an easy fix for someone who has the time, I've bought way too many power supplies since then and don't need it.Dual output, +/- 40 VDC, up to 1 amp with current limit on front panel. Sense connections on rear panel.Free for collection in the Pasadena area of Los Angeles.Cheers,RuairiP.S. I have the missing knobs too***Gone***

author: macboy
author_rank: Super Contributor
timestamp: June 23, 2017, 06:17:17 pm
content: I can tell you exactly which capacitors are dried up and causing the wandering readings.Do you have the service manual? I can pass it on to you (or new owner) if not.

author: ruairi
author_rank: Frequent Contributor
timestamp: June 23, 2017, 08:38:47 pm
content: Thanks Macboy, I do have a PDF of the service manual but it's not a great scan, perhaps yours is better? If it will attach here please do and if not feel free to PM me.I'm on a huge clear out and focusing drive in advance of a new project so I won't have time but I'm sure the new owner would appreciate any info you might have. It would be a nice bench supply for an interested beginner.Cheers,RuairiP.S. I have an older B&K RF Sig Gen and an old tube Tek scope that will be going too. More info and pics soon.

author: alm
author_rank: Super Contributor
timestamp: June 23, 2017, 10:18:01 pm
content: These are nice power supplies. Pretty much all standard parts except the voltage regulator IC and maybe the panel meters. Very straight-forward circuit, so repair should not be difficult. Especially since one of the channels is fully functional. These are pretty much two LQ-412s stuck together sharing a single case and transformer. Free pick up is a great deal for anyone local to LA.Hereis what looks like a very readable scan of the manual with schematics.

author: nidlaX
author_rank: Frequent Contributor
timestamp: June 24, 2017, 06:10:31 am
content: PM sent.

author: Smokey
author_rank: Super Contributor
timestamp: June 24, 2017, 06:44:36 am
content: Ahhhh.. Im one post too late. There's always room on the bench for another power supply! Let me know if you still want to get rid of it.

author: ruairi
author_rank: Frequent Contributor
timestamp: June 24, 2017, 07:18:41 am
content: No worries Smokey, it's oh hold until tomorrow afternoon for nidlaX. If for some reason that doesn't work out you'll be next in line.

author: ruairi
author_rank: Frequent Contributor
timestamp: June 24, 2017, 11:32:29 pm
content: PM'd you Smokey, nidlaX is not taking the unit.

author: macboy
author_rank: Super Contributor
timestamp: June 28, 2017, 03:27:16 pm
content: For posterity, here are a couple of documents for the custom Lambda-made regulator IC. In the service manual it is called FBT-00-128, and in their semiconductor catalog, it is called LAS3700. The service manual linked above is the same one I have.There are four (or more) smallish axial electrolytics, that were dried up and useless. One for each display board negative power supply filter cap, and another similar cap on each side. Found them easily by looking for high ripple voltage across caps, then by pulling one leg of the suspected cap and measuring it. The negative rail is used to for the display IC (ICL7107) reference voltage, so the dried up cap causes the reading to jump randomly. I bodged replacements onto the backside of the boards since that was easier to access and still fit inside the case.In my unit, I tweaked the meters by changing the values of the RC oscillator so that the display update rate was much faster and the integration period was a multiple of 1/60 second. That improves rejection of 60 Hz noise which had been a problem for me. I also modified my displays so that they go from 0-999 mA (1 mA resolution) instead of 0.00-1.00 A (10 mA resolution). This is a single resistor replacement followed by calibrating the current display. I can post details of that later when I can get at my notes.

author: ruairi
author_rank: Frequent Contributor
timestamp: June 28, 2017, 04:35:05 pm
content: Great info, thank you. I'll pass on to the new owner of the unit.Cheers,Ruairi