Repair/Restoration Adret 103A Current and Voltage standard - Page 1
Forum section: electronics / repair

author: BFX
author_rank: Frequent Contributor
timestamp: November 22, 2016, 09:29:32 pm
content: Few months ago I bought this guy as broken and finally I got service manual, now is time to repair.First of all I found that +- 15V rails are not so good.Two 15ohm resistors are broken but why? After replace magic smoke escapedAha tantalum capsboth at output had resistance around 50ohm (not so common that they are not fully shorted).Now is time to order some spare parts.Questionis what to use as replacement for those tantalum bastards. What is your suggestions guys?Again tantalum or electrolytic or ceramics? Because most of them are 4.7uF/20-40V.

author: BFX
author_rank: Frequent Contributor
timestamp: November 23, 2016, 07:28:11 pm
content: Next part is about Mains Dropout Protection.Function of this circuit is not so clear for me.If battery is connected all digital part is powered, also in case if main switch is off.Surprise for me was that Q4 is on board connected differently collector - emitter are upside down.Simulation is exactly like is it connected on PCB.I did some simulation and behavior of circuit is different, but I can't find any bad component.

author: acbern
author_rank: Frequent Contributor
timestamp: November 23, 2016, 11:15:11 pm
content: Would not use Tantalums, these days organic electrolytics are better (goof HF behaviour, no nasty failure modes). I used Oscons everywhere on my 4910 after the tantalums started to die.

author: BFX
author_rank: Frequent Contributor
timestamp: November 25, 2016, 09:05:17 pm
content: Quote from: acbern on November 23, 2016, 11:15:11 pmThx I have the same opinion.Would be great guys to explain me how It works, this dropout protection, because I'm totally confused from this circuit

author: Kleinstein
author_rank: Super Contributor
timestamp: November 25, 2016, 10:27:41 pm
content: To me that dropout protection circuit looks like a charging circuit. If mains supply is there, the battery is charged up to a voltage of about 5.2 V + drop of D2.

author: BFX
author_rank: Frequent Contributor
timestamp: November 27, 2016, 08:13:17 pm
content: Quote from: acbern on November 23, 2016, 11:15:11 pmWhat do you think about following caps as replacement of those tantalumshttp://uk.farnell.com/kemet/c340c475m5u5ta/cap-mlcc-z5u-4-7uf-50v-rad/dp/1457712http://uk.farnell.com/kemet/a759eq475m2aaae160/cap-alu-polymer-4-7uf-100v-radial/dp/2614109http://uk.farnell.com/rubycon/35zlg4r7mefc4x7/cap-alu-elec-4-7uf-35v-rad/dp/1281822http://sk.farnell.com/multicomp/mcrh35v475m5x11/cap-alu-elec-4-7uf-35v-rad/dp/1902916

author: Theboel
author_rank: Frequent Contributor
timestamp: November 30, 2016, 10:46:03 am
content: Hi BFX,Just curious becaused I can not find the schematic,Could You upload the Voltage reference parts and or parts of service nabual about it. Thank YouI replace handful tantalum cap from my HP 8590L with OSCON SA cap and guest what the noise floor get down measurably I do not say spectacular but measurable.

author: BFX
author_rank: Frequent Contributor
timestamp: November 30, 2016, 06:53:56 pm
content: Quote from: Theboel on November 30, 2016, 10:46:03 amSorry, it takes long time and effort to find this service manual. It's not so good, but better like nothingHere is ithttp://www.eternal.sk/Adret103A.zipAbout capacitors ... I can't find OSCON SA 4u7/36V at Farnell. What about caps which I mentioned?

author: BFX
author_rank: Frequent Contributor
timestamp: December 17, 2016, 01:22:51 am
content: Good newsunit is working(see photos)Primary problem of course tantalum caps.All was replaced and also 15 ohm resistors in +- 15v power supply.That was root cause. Additional components shouldn't be changed but during investigation it was.Next step is confirm the specs, clean the unit and keyboard contacts and do the calibration.Sorry photo is not so good, but now is 2:30AM and I need to sleep

author: BFX
author_rank: Frequent Contributor
timestamp: December 18, 2016, 04:37:37 pm
content: Some basic measurements:)Looks very good, but I think that calibration is necessary, question is if official calibration is necessaryProbably I should replace some resistors which are out of spec and I found it during repair.