SOLD (UK) Tenma PSUs to repair - Page 1
Forum section: electronics / general

author: TopLoser
author_rank: Unknown
timestamp: September 13, 2015, 04:54:22 pm
content: 2 of these:http://uk.farnell.com/tenma/72-8340a/power-supply-1ch-60v-1-6a-adjustable/dp/2216729One allows you to set V/I and reads back ok, but the output is always on regardless of the ON/OFF button.Other has fixed output voltage of 19V, current limit seems to work as does output ON/OFF1 of these:http://uk.farnell.com/tenma/72-8345a/power-supply-1ch-36v-3a-adjustable/dp/2216730Seems to work but the current reading always displays 0.00 even though the actual current is as set. Voltage readings are fine.Can try and pack them to get the weight under 2Kg so they can go Royal Mail overseas but don't moan if they reach you a bit battered.£10 each plus shipping costs (£5 UK, £15 and up anywhere else sensible)Or buy all 3 and still pay £5 shipping if you're in the UK.ALL GONE

author: cowana
author_rank: Frequent Contributor
timestamp: September 13, 2015, 05:13:23 pm
content: QuotePM sent

author: Monkeh
author_rank: Super Contributor
timestamp: September 13, 2015, 05:15:38 pm
content: Quote from: TopLoser on September 13, 2015, 04:54:22 pmI'll take that if it's still going.

author: TopLoser
author_rank: Unknown
timestamp: September 13, 2015, 05:17:39 pm
content: Quote from: Monkeh on September 13, 2015, 05:15:38 pmSold to Monkeh.

author: TopLoser
author_rank: Unknown
timestamp: September 13, 2015, 05:18:19 pm
content: Quote from: cowana on September 13, 2015, 05:13:23 pm12 minutes too late, already sold to Macbeth sorry.

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2015, 05:23:08 pm
content: PM sent

author: Cloud
author_rank: Regular Contributor
timestamp: September 13, 2015, 05:24:51 pm
content: Quote from: TopLoser on September 13, 2015, 04:54:22 pmIs this one still available?

author: TopLoser
author_rank: Unknown
timestamp: September 13, 2015, 05:39:13 pm
content: Quote from: Cloud on September 13, 2015, 05:24:51 pmNo, sold to Macbeth like I already posted.

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2015, 05:48:07 pm
content: Only the 19V stuck one is left....

author: Cloud
author_rank: Regular Contributor
timestamp: September 13, 2015, 05:54:11 pm
content: Oh silly meI only checked top post and I saw that its not crossed

author: Deathwish
author_rank: Unknown
timestamp: September 13, 2015, 06:03:11 pm
content: PM sent

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2015, 06:15:12 pm
content: Ian, please use Yodel as a courier to send the PSU to Deathwish. He has such a good rapport with them that it would be a shame to break it.Just like me and DHL. Only 9p, but they wanted 80 pounds as extortion to deliver it. At least I got a VAT invoice from them, so we could claim it back from the Receiver.

author: Deathwish
author_rank: Unknown
timestamp: September 13, 2015, 06:17:02 pm
content: Quote from: SeanB on September 13, 2015, 06:15:12 pmGrrrr. Hit squad on its way to your house. Ian sends his kit by a reputable and decent courier, never lost one from him yet.

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2015, 06:36:14 pm
content: Quote from: Deathwish on September 13, 2015, 06:17:02 pmLast hit squad got taken out by my neighbour. Ex MK. If the dam drops another 7m they might find them..........

author: Deathwish
author_rank: Unknown
timestamp: September 13, 2015, 06:40:47 pm
content: Meh, no one can take out the TMNT's ....

author: Macbeth
author_rank: Super Contributor
timestamp: September 16, 2015, 04:06:18 pm
content: Fault located - output MOSFET shorted. IRF3710 on order.Also customer had managed to get into the calibration mode and turn a 36V model into a 60V modelThis allowed the volts to go up to 40V then dropped in half at anything over. Found the secret mode (power on with both volt and current knobs pressed in). You can change the model from Manson 6016/3630/2050 (Tenma 72-8340/8345/8350) using the output button. I will also need to recalibrate it, procedure herehttp://www.farnell.com/datasheets/1769550.pdf

author: Monkeh
author_rank: Super Contributor
timestamp: September 16, 2015, 05:09:14 pm
content: Quote from: Macbeth on September 16, 2015, 04:06:18 pmStill looking at mine, I have a sinking feeling the PIC's got a bad ADC channel.

author: Macbeth
author_rank: Super Contributor
timestamp: September 16, 2015, 06:36:25 pm
content: Quote from: Monkeh on September 16, 2015, 05:09:14 pmI don't think so. Your fault is displaying output current of 0? Well guess what, having had a stab at calibrating mine its volts is now spot on, and its current setting is spot on, but its current read-out is 0My guess is someone attempted to make some sense of the current calibration instructions and fecked it up, like I did. Then sent it back.I just used my DMM with some short fat wires to measure current and tuned in the PSU to those.According to the instructions you need an electronic load with CC and CR. I could use my HP6632B as a 0-5A CC load, but don't have a CR load. It seems any old shunt that can cope with >5A is ok, no resistance specified. The voltage you are meant to read across the shunt is 18V, or half the full scale 36V of the PSU, so I guess the CR load is being used to match the shunt, but I measure only 33V coming from the PSU during calibration? Bit of an odd divider.There must be some way to do it without a CR load but I can't quite figure out from the instructions exactly what the PSU is expecting for it to calibrate its own internal ammeter. Any ideas?

author: Monkeh
author_rank: Super Contributor
timestamp: September 16, 2015, 06:44:16 pm
content: Well, shit!I did have a go with a load of transformer primaries at getting the desired voltages (faking constant resistance the annoying way), and I've managed to tighten up the current preset quite nicely, but still no reading.We may just have to build some constant resistance loads.It wants 18V on the PSU output, not over the shunt. The shunt can be the one built into a meter, it doesn't matter. At least, that's how I've interpreted it..

author: Macbeth
author_rank: Super Contributor
timestamp: September 16, 2015, 07:06:34 pm
content: Quote from: Monkeh on September 16, 2015, 06:44:16 pmWell the diagram shows 18V across the shunt and the instructions say to alter the CR until you get 18V. Lots of PSUs including my HP6632B specify to use a shunt and read the voltage across it and then perform the I=V/R calculation for accurate current calibration. I've not seen this method of using a constant resistance load before.Normally, yes you can ignore all that uber cal-lab standard stuff and just go for using the current range and shunt in your DMM. This works great with the Tenma PSU for the currentsettingcalibration (the DAC), but clearly not the currentreadingcalibration which is the ADC.I still can't quite fathom the instructions, they mention LCD reading but I think they mean DMM reading, etc... Typically poor Chinglish translation.

author: Monkeh
author_rank: Super Contributor
timestamp: September 16, 2015, 07:30:48 pm
content: I'm pretty certain they don't want you to put 18V across the shunt. And I don't see a diagram showing it..Steps 8, 9, and 10 appear to be for calibrating the ADC reading. 9 and 10 should show live readings, and mine stays mute throughout.

author: Monkeh
author_rank: Super Contributor
timestamp: September 17, 2015, 06:56:32 pm
content: So, having blown up a couple MOSFETs, I decided to destroy a hairdryer instead.Now I have an ammeter! It's a tad off on the high end of the scale, but I'll fix that another time. The hairdryer remnants were about to catch fire.

author: Macbeth
author_rank: Super Contributor
timestamp: September 17, 2015, 07:07:53 pm
content: LOL! Glad to see you are getting somewhere.I tried using my 6632B as a DC load. I programmed all the amps in and it works in that capacity, but I can't quite understand what the darn instructions are requesting. The 18V - is this something to measure across the entire load? So the PSU puts out 33V @ 0.63A, then 33V @ 2.7A and then it has to be loaded so much that the volts drop to 18V? and then you twiddle the knob for the currents to match?Hmm... I've got hairdryers, toasters, old AVO 8, etc to use as load I guess.

author: Monkeh
author_rank: Super Contributor
timestamp: September 17, 2015, 07:13:20 pm
content: Pretty much. It wants you to adjust the resistance until you hit half scale voltage in CC mode. Not really sure why, but it works. My setpoints are pretty much bang on, but the ammeter is a bit off above 1.5A or so (gets to about 150mA offset at 3.2A.. I can live with that for now).The output toggle works in cal mode, I strongly recommend using it to avoid, well, setting a hairdryer on fire. Also.. use croc clips and take the sleeve off. I nearly ruined a couple hooks by melting the wire into them, thinking cap was put down somewhere.. If you're careful the hairdryer might survive!

author: Macbeth
author_rank: Super Contributor
timestamp: September 17, 2015, 07:42:44 pm
content: One thing obvious with these is they have switched from using the Atmel AVR board like in Mikes teardown:to a Microchip PIC18F87K90 - 80 pin. The spare 3 pin header is wired to the RX2/TX2 port, which would imply some form of serial control is possible, and the 5 pin ICSP header is there too.I did finally get around to upgrading my TL866CS to a TL866A. As I 99% expected, I couldn't read the contents of the PICBut can its fuses and memory be erased like the AVRs can?It looks like a good hackable board ready made for new PIC firmware to give computer control and a much simpler method of calibration.Oh yes, I checked the serial port and nothing on it, nothing on the scope or my RS232 USB device at all.

author: Monkeh
author_rank: Super Contributor
timestamp: September 17, 2015, 07:45:05 pm
content: Yeah, these A models have a totally redesigned panel. Checked out the serial and such as soon as I saw it, indeed nothing happening, probably never implemented.Sadly, I only have a PICKit 2 so I can't play with the firmware on these.

author: Macbeth
author_rank: Super Contributor
timestamp: September 17, 2015, 10:25:00 pm
content: This is the 60V PSU front panel. Note the obvious hand soldered parts including a few resistors around the header, R34-R36. My 36V version is the same but the immediately obvious thing is those resistors are different. Sorry, didn't take a pic of that panel, but can do so if anyone wants.Clearly a serial port is on offer and the PIC programming port... Hmm....