Why these machines come back in good shape
TPS 4000 and TPS 5000 were built around a power module cooled by a forced flow of air, with a separate wire feeder and an interconnection cable. Such a layout moves heat and vibration away from the electronics, so the boards age more slowly than in compact machines. In machines that reach us after about ten years of single shift work the power path is usually sound, but that is an observation from our workshop, not a statistic of the manufacturer.
What does wear are the moving parts and those through which the wire or the coolant passes. Below are the assemblies in the order in which they come in for repair in our service workshop.
What wears and how you recognise it
The power module
The power module fails rarely, but when it does, it is the most expensive item in the estimate. The symptoms can mislead: the machine starts, holds the current at 150 A, and at 300 A loses voltage or goes into an overheating error after a minute of arc. A frequent cause is not the module itself, but a layer of welding dust on the heat sinks that works like a blanket.
The second typical case is a short circuit after metal particles have been drawn inside. A machine standing under a grinder catches this within a year. That is why in the service workshop, before connecting the supply, we take off the cover and look at the module, the connectors and the tracks.
Fans and the flow through the channels
Fans are a wear part. After a few thousand hours the bearing starts to whistle, the speed drops, and the machine loses duty cycle although it still works. The symptom is simple: at full current a temperature error appears after 2 to 4 minutes, which was not there before.
The replacement is cheap, roughly 150 to 400 PLN net apiece plus labour. Neglecting a fan costs you the power module, so this is the best invested part in the whole machine.
The wire feeder
The VR feeder runs through the whole arc time and collects dust from the wire. What wears are the rolls, the inlet guides, the pressure unit and, more rarely, the motor with the encoder. The symptoms: the wire runs unevenly, the current jumps by more than ten amperes, on the weld face you see cyclic narrowings.
We check this by measuring the feed speed over a length, not by eye. We set 8 m/min, measure the wire unwound in 30 seconds and compare. A deviation above 5 percent or instability between attempts means a change of rolls, and sometimes of the motor.
The cooling unit and the coolant circuit
The cooling unit is the second reason, after the fans, for a drop in output. The pump loses output, the heat exchanger clogs from the inside, and the coolant turns into a deposit after years. The symptom: the torch heats up at 250 A although it is rated for 400 A, or the machine reports a flow error on a longer weld.
We measure the flow on the return and the temperature of the coolant after 10 minutes of work under load. If the flow is lower than the requirement of the manufacturer, we change the coolant, flush the circuit and only then assess the pump. The coolant itself is a cost of several dozen PLN, the exchanger and the pump roughly 600 to 1,500 PLN net.
The interconnection cable
The interconnection cable between the power source and the wire feeder carries current, gas, coolant and control signals. It is the most exposed element in the whole set, because it lies on the floor, gets driven over by a truck and bent at every move of the station. The damage is usually internal and cannot be seen from the outside.
The symptoms: the arc breaks at a certain position of the cable, coolant leaks after a few minutes of work, communication errors with the feeder. A new cable of 4 m is roughly 2,000 to 4,500 PLN net, so when pricing a machine we check it separately and describe it in the product card.
The control panel
The keypad membrane and the knobs do not like spatter and solvents. After years a key stops responding, and the encoder jumps values in both directions within one turn. The machine still welds, but setting a parameter takes three times longer.
A change of the membrane or of the encoder is roughly 500 to 1,500 PLN net. It is worth doing before the sale, because the panel is the first thing the next user judges.
What comes on top with CMT machines
In CMT the wire is withdrawn and fed at a high frequency, so there is a drive in the torch and a wire buffer between the feeder and the torch. These are two assemblies that a plain TPS does not have.
The drive in the torch has its own rolls and its own bearings, working with a reversing motion. A worn drive shows itself as a loss of repeatability of the short circuit. The wire buffer has to move freely, and a dirty one adds resistance that spoils the synchronisation. These are, however, conclusions from the end of the list, not from its beginning.
A loud CMT process: the order of checking
A loud process and spatter do not on their own point to an assembly. The same test comes out loud with a worn drive and with a badly chosen program, which is why the diagnosis is made step by step, from the cheapest things to the most expensive.
- Program: whether the chosen characteristic fits the material, the wire diameter and the gas, and whether the software version is the one the program was made for.
- Material: grade, thickness, condition of the surface. Grease, rust, zinc coating and moisture change the course of the short circuit.
- Gas: type and flow in line with the program, tightness of the hose and the regulator, no draught at the station.
- Consumables: rolls, pressure unit, liner, contact tip, the way the cable is laid. A worn tip gives a symptom deceptively similar to a worn drive.
- Settings: correction of the arc length and of the dynamics, the height of the free wire stickout, the angle and the travel speed of the torch.
- Only then the assemblies: the drive in the torch, the wire buffer, the interconnection cable.
When we take in a CMT machine we run a test on 1 mm sheet and judge the process by sound and by the weld face. If after going through the whole list, with a checked program and new consumables, the process is still loud and repeatedly throws spatter, only then do we look for the cause in the drive, the buffer or the cable.
What you can check yourself, without opening the machine
Before you order service, sift out the faults you can clear on the spot in a quarter of an hour. You do the following with the machine closed, without taking off covers and without measurements on live parts. Quite a few of the reports that reach our service workshop end on one of these items.
- Read the error code from the panel and look it up in the operating manual of the machine. The manual says what the machine reports and what the user may do about it.
- Check that the air inlet and outlet are clear and that the machine does not stand against a wall or under a grinder. Dust alone can lower the duty cycle by more than ten percent.
- Check the level and the colour of the coolant in the tank of the cooling unit, in the way described in the manual. Dark coolant with a deposit is a signal to change it, not to top it up.
- Change the contact tip and blow through the liner of the torch. Most jumps of current come from there, not from the power module.
- Look over the interconnection cable and the earth cable along their whole length: chafing, crushing, traces of coolant, a loose earth clamp.
If the symptom does not go away after these steps, the cause lies deeper and further diagnosis needs the machine opened or measurements under voltage.
What staff prepared to work to the manual do
The steps on this list are carried out by a person trained to work on this equipment, according to the manual of the manufacturer and the rules on work on electrical installations. The TPS manual gives the time after disconnection of the supply at which the covers may be taken off, because the capacitors of the intermediate circuit discharge with a delay.
- Taking off the covers after disconnecting and securing the supply and after waiting the time given in the manual; assessment of dust, connectors, traces of short circuits and leaks.
- Blowing the heat sinks with compressed air at reduced pressure, from the side, not straight at the board.
- Measurement of the supply voltage under load, at the supply socket, with an instrument of a measurement category proper for that installation. A clear drop of voltage under load against the value without load, outside the tolerance from the rating plate of the machine, explains the loss of current without any fault of the machine.
- Measurement of the coolant flow on the return and of the coolant temperature after the load test.
- Reading of the error log and of the service data with the tool of the manufacturer.
If you have no such person on site, stop at the previous list and report the machine to a service workshop. A cover taken off and a meter in hand are not a stage of diagnosis for the user.
The load test, step by step
None of the faults above shows itself in five seconds of arc. That is why we load every machine for real, on material, in the rated conditions from the rating plate. The procedure has four fixed elements.
- Current: the rated value from the rating plate for the chosen point of the cycle, for example 400 A at 40 percent.
- Cycle: a period of 10 minutes, of which 4 minutes of arc and 6 minutes of break, in line with the same point of the rating plate.
- Time of the test: at least three full periods, that is 30 minutes, so that the temperature of the machine can settle.
- Criterion: in every period the machine holds the set current and voltage for the whole permitted arc time, without a drop of current and without the thermal protection tripping.
In the report we write down the ambient temperature and the supply voltage, because both change the result and without them the test is not comparable. Separately we check the reaction to exceeding the cycle: if we deliberately extend the arc time beyond the value from the rating plate, the thermal protection is to trip, and the machine is to return to work after cooling down. This is correct behaviour and we describe it as such, not as a fault.
| Stage | What we do | What we read |
|---|---|---|
| 1. Internal inspection | service workshop, after disconnecting the supply and waiting the time from the manual: covers off, assessment of dust, connectors, traces of short circuits and leaks | the decision whether to connect the supply at all |
| 2. Cold start | start up, going through the menu, test of all keys and knobs | working order of the panel and of the memory of settings |
| 3. Wire feeder | measurement of the feed speed at 3 set values | deviation in percent, stability between attempts |
| 4. Short arc | a weld on 3 mm sheet, 120 to 180 A | stability of ignition, amount of spatter |
| 5. Long load | load test at the rated current in the duty cycle from the rating plate, for example 400 A at 40 percent, that is 4 minutes of arc in 10 minutes | whether the machine holds the current in the permitted cycle; tripping of the thermal protection after the cycle is exceeded is correct and is not a fault |
| 6. Cooling | flow on the return and coolant temperature after the test | condition of the pump, of the exchanger and of the flow through the circuit |
| 7. Cable and torch | moving the cable under load, check of tightness | breaks in the arc, leaks, communication errors |
What you find in the description of the machine
We do not judge a machine by the date on the rating plate, only by what the test showed. In the product card we give the result of each of the seven stages, the list of replaced parts, the list of the set and any missing items. You get the inspection report with the extended service package.
On top of that comes the first year of the basic service package in the price of the machine. You buy further years, then repairs come out cheaper, and for the time of repair we provide a replacement machine.
When a repair stops paying
A simple rule: if the estimate exceeds half the market value of a sound unit, the repair is already an investment and not maintenance. With TPS 4000 this is usually the moment when the power module and the interconnection cable have to be replaced at the same time.
| Repair | Net cost, indicative | Decision |
|---|---|---|
| Fans, coolant, rolls, panel membrane | 800 to 2,500 PLN | always worth it |
| Pump and exchanger of the cooling unit | 600 to 1,500 PLN | worth it |
| Interconnection cable 4 m | 2,000 to 4,500 PLN | worth it if the rest is sound |
| Complete wire feeder | 4,000 to 9,000 PLN | to be counted, sometimes a separate feeder is cheaper |
| Power module | 6,000 to 12,000 PLN | only with the rest in good condition |
| Power module plus cable plus feeder | above 15,000 PLN | better to change the machine |
In that last case it makes more sense to hand the machine over in part exchange. We value it in our buy back, also in a faulty state, and deduct it from the next purchase. For the time of the changeover you can take a machine from rental, so that the job does not stop.
Before you decide on a repair, compare it with the five-year cost of running a welder (guide in Polish), because that shows where the money really goes.
Bring the machine in for a test
We do the diagnosis with a load test in Krotoszyn, usually within one working day. Call before you come, so that we can prepare the station and the coolant, or look into the category used MIG/MAG, where every machine is checked in our service workshop.