6 foot challenger tank pcb repair help needed - Page 1
Forum section: electronics / repair

author: pickleit
author_rank: Contributor
timestamp: May 29, 2019, 03:36:44 pm
content: HiI need some help with a pcb that was brought in for repair many months ago (july/Aug 2018 i think). The PCB was from a 6 foot model challenger tank.The pcb had suffered damaged after the battery packs had been connected in reverse polarity.5 components suffered physical damage and 1 was detached from the board. Also there was damaged to the pcb substrate too. The components consisted of 3 tantalum caps, 1 NPN transistor and 1 quad op-amp.I repaired the damage to the pcb substrate and damaged pad with fibreglass mat, soldermask, CW2500 and copper foil.After asking around on a number of forums, maybe even this one, I managed to identify the damaged components.The components are:1) NPN transistor.2,3,4) tantalum capacitors.5) Quad channel op-amp.To make this job far more difficult than it should of been, the board didn't have any reference designators or values, no schematics were available and the customer didn't really know what the board did.Also the customer said that the board ran off 24V battery packs, but recently he said that it actually runs 12V.My questions are:1) does anyone know what this board is supposed to do?I think it is some sort of motor controller. Customer thinks it controls the turret of the tank.2) In order to test the repaired board I set my bench power supply to 12.03V (constant voltage. C.V.). I then powered off the bench power supply and connected it the pos and neg leads of the pcb. I think the pcb has an on/off toggle switch, so before powering on the bench supply I toggled the switch to the "off" position. When I power on the bench power supply, why does it change to C.C. mode and show 270mV and 124mA?I just want to confirm this board works board works before I hand it back to the customer.Thanks David

author: tszaboo
author_rank: Super Contributor
timestamp: May 29, 2019, 03:39:19 pm
content: Hi. Welcome to the forum. You should make a photo of the damage and the entire PCB and upload it here, so we have a better understanding of what is going on.

author: pickleit
author_rank: Contributor
timestamp: May 29, 2019, 03:43:24 pm
content: I am trying to upload photos right now, but this forum has such a low upload limit. 2MB limit for up to 25 attachments!!!!!

author: pickleit
author_rank: Contributor
timestamp: May 29, 2019, 04:18:25 pm
content: More photos of the PCB.before photos, showing the damage

author: pickleit
author_rank: Contributor
timestamp: May 29, 2019, 04:32:52 pm
content: HiJust noticed that I have put component #2 (tantalum cap) on backward. I will retest and report back.

author: pickleit
author_rank: Contributor
timestamp: May 29, 2019, 04:37:12 pm
content: HiI have changed the tantalum capacitor so that the side with the line now points the other direction.The bench supply now shows 340mV and 121/2ma C.C. when connected to the powered "off" pcb.

author: Chris56000
author_rank: Frequent Contributor
timestamp: May 29, 2019, 05:20:00 pm
content: Hi!What make and model is the tank the pcb came from?There seem to be what looks like "Chall 65136" handwritten on the component–side of the PCB – I wonder if you've tried researching a used replacement board?Chris Williams

author: pbarton
author_rank: Frequent Contributor
timestamp: May 29, 2019, 07:25:57 pm
content: I think that I would send this guy an email, with suitable photo attachments to see if he can identify it.http://www.mark-1-tank.net/NewMark1/mark1tankhome.htm

author: GreyWoolfe
author_rank: Unknown
timestamp: May 29, 2019, 07:58:11 pm
content: Quote from: pickleit on May 29, 2019, 03:43:24 pmUse Irfanview to reduce the file sizes of your pics. I reduce mine to 1024x768 and they show up just fine.

author: tszaboo
author_rank: Super Contributor
timestamp: May 29, 2019, 08:59:38 pm
content: It is definitely some controller, there are high current traces, and those AT87xxs are microcontrollers.That is one weird board though.I think the traco dc-dc converter might be also damaged, that has internal IC and inductor potted, so the damage might not be visible immediately. Try removing it and powering it without it.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: May 30, 2019, 01:46:52 am
content: Quote from: pickleit on May 29, 2019, 03:36:44 pm1.) It definitely is a motor controller. Those components below the board are the power transistors (Mosfets), which do the actual switching of the high currents. Note the expression 'switching', as the proportional 'variable speed) control of the motors is via PWM, which is generated by the microcontrollers.The presence of more than one µC hints at the board controlling more than one motor. Probably, it is one Atmel for each motor, or one for two motors. To identify that, you would have to trace the power transistor circuits. They are probably made up of H-bridges, with different numbers of transistors in parallel, maybe.2.) What did you set as CC/Current limit value initially? Might that be too low? Also, some circuits designed to work off a battery do not start well is presented with a current limited power supply.

author: pickleit
author_rank: Contributor
timestamp: May 31, 2019, 12:42:02 pm
content: Quote from: Chris56000 on May 29, 2019, 05:20:00 pmAll I can tell you that the pcb is custom designed for the tank it comes from. I have no information if the rest of the tank is any particular brand.

author: pickleit
author_rank: Contributor
timestamp: May 31, 2019, 06:47:57 pm
content: Quote from: Neomys Sapiens on May 30, 2019, 01:46:52 amAnswer to question 2: I set the bench supply to 12V CV then turned it off. I then connected the bench supply to the pcb them powered on the power supply. When I turned the bench supply back on it showed as being in CC mode; showing 270mV and 124mA.

author: pickleit
author_rank: Contributor
timestamp: May 31, 2019, 06:48:49 pm
content: Quote from: Chris56000 on May 29, 2019, 05:20:00 pmIt's a custom designed PCB.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: May 31, 2019, 07:14:31 pm
content: Quote from: pickleit on May 31, 2019, 06:47:57 pmYes, so there are two possible reasons your PS goes into CC: your current setting is too low for the board to start properly or you have a short. What happens if you turn up your CC value at the PS?As hinted above, I was brought a NiCad high speed charger for repair/diagnosis which was intended to operate from a car battery. My regular bench PS did not get it to start WITHOUT or WITH a load. Had to fire up the 20A HP AND use a sizeable capacitor to get it to start. After that, current was rather low.

author: pbarton
author_rank: Frequent Contributor
timestamp: June 03, 2019, 09:40:26 am
content: I sent an email to Mark (his email address is given herehttp://www.mark-1-tank.net/NewMark1/mark1tankhome.htm).Apparently this in an old speed control and sound unit, possibly from a Challenger 2.While the 6 foot tank market may be small, the board is not what I would consider to be a “custom designed PCB.”Mark is importing these from 'his' supplier in Russia. He is not revealing the source, as he is attempting to control distribution.“That unit is no longer in production, being superseded by an updated version, it originally came from my Russian suppliers, yes they do an updated version that is £375 for 12v and £400 for 24v, there are no schematics for these units.I am presuming the Challenger 2 is an older Gearbox version, what condition are the tracks in ?I also do the latest spec 24v chain drive versions with CNC track upgrade another speed control with an advanced sound system, this requires separate speed control for elevation as well, price for that upgrade is £650.”