Curious Case of PACE TJ-70 - Page 1
Forum section: electronics / repair

author: shuvodutta
author_rank: Contributor
timestamp: June 19, 2019, 04:44:52 pm
content: This is going to be a long post. My new (?) PACE TJ-70 ThermoJet was blowing fuse on my PACE MBT-250. I’ve discovered an interesting & never-heard-before issue while debugging.I’ve recently scored a PACE lot (This is the second lot I’ve scored, will share the story in another blog post later.) and received PACE TJ-70 ThermoJet as part of it. TJ-70 (without any nozzles, I’ve ordered them separately from another seller.) was the main reason for buying this lot (Used one sells for quite a high price on ebay.) and I immediately grabbed the unit after receiving it. The unit looked new & unused, my enthusiasm got heightened.I’ve connected it to one of the PPS-80 stations (received them as part of the lot, work fine though was described as ‘Does Not Power On’!), have set the temperature dial, plugged the hose to the air outlet and switched on PPS-80. TJ-70 started heating and the onboard switch controlled the pump reliably, I started feeling happy.My happiness got dimmed soon once I’ve found out that almost no air is coming out from the handpiece (from the heater bore where the nozzle should go, to be precise.). A closer inspection revealed that the end cap of the heater assembly is loosened and moved away from it’s initial position. Now it so happened that I had another heater assembly (They get sold for crazy prices!) which I’ve received as part of the lot, lucky me. I quickly went through the required PACE Manuals for TJ-70 Heater Replacement and removed the original assembly from my unit (eevblog-forum-repair-pace-tj70-01.jpg). The fault looked repairable once the assembly was out of the TJ-70 (no need for the spare assembly.). Basically the rubber end cap (which acts as a seal for the metal cylinder used for air transport.) is attached on a metal collar which gets attached to the end of heater assembly by means of press fit (eevblog-forum-repair-pace-tj70-02.jpg). Once I’ve moved it to the right position and applied a little pressure carefully by mini pliers, it was good to go. I’ve reassembled the unit and tested it again on PPS-80, stream of hot air swept my almost teary eyes. What I’ve failed to understand then that it was not the end but the beginning.So, confident me (!) freed up one channel on my trusty MBT-250, plugged TJ-70, switched it on and SMOKE! No, not really but the station died (not powering on) and the sound it emitted from it’s beeper for few seconds before it went numb was it’s last cry to my ears. I took it out immediately and as I’ve guessed; got a blown mains fuse. Once replaced with the spare one, it came back to life. I’ve suspected my 220v-110v Step-Down Transformer for this issue but the transformer checked out fine. So after testing MBT-250’s functionalities, I’ve plugged in TJ-70 once again (assuming that the blown fuse was a coincidence.). That channel was initially off and everything was fine. I’ve pressed the Set button and started increasing the temperature, everything was normal for the first few seconds but after that all L.E.D.s went off and the beeper let out the same cry. I’ve disconnected TJ-70 immediately and checked the replacement fuse again, it was not blown and the unit powered up fine without TJ-70 connected. To be sure I’ve connected TJ-70 to another channel on MBT-250 while it was powered on and the same incident took place, even it entered in CAL Mode after that event (I think MBT-250 got a spurious reset but more on that later.). It was evident that MBT-250 was not in love with TJ-70 (They’re supposed to be,this combination is officially supported by PACE.). I’ve started suspecting MBT-250’s per channel power delivery capability (TJ-70 is a 70W handpiece, my all other PACE handpieces need lesser power than this.) but my assumption has been proven wrong soon.It was bugging me that PPS-80 is driving this TJ-70 handpiece without any trouble (!) but the same handpiece overloaded my MBT-250 (clearly the main transformer was trying to deliver too much power on it’s secondary winding, it increased power draw on primary in turn and the fuse protection kicked in. FUSE became very famous after Dave’s Video on Weller and it looks FUSE do their job well. Believe me, these PACE units are solidly built; electrically and mechanically, they don’t blow fuse without serious issues!). So, to have a better understanding (or 3 Sample Check) I took out my PACE ST-115 units (They are standby equipment, I don’t use them on a regular basis. MBT-250 & ST-115 units are from the first PACE Lot I’ve scored.). Both the ST-115 units I’ve, checked out fine for functionalities (tested with PACE PS-90 Soldering Handpiece.) but started showing OCE (Over Circuit Error in PACE Terminology and means something’s wrong with the Heater Assembly.) when connected to this TJ-70 (TJ-70 was heating up though.) but none of them has blown fuse. I became sure that power delivery capacity of the station (ST-115 is a single channel, 120W unit.) has nothing to do with this issue and something is wrong with the TJ-70 itself.I was confused and decided to finish the heater burn in procedure for TJ-70 (as it was a brand new handpiece.) using PPS-80 and it went well (analog temperature controller on PPS-80 did not complain about anything!).I’ve checked the heater and sensor resistance of both (original & spare) the TJ-70 Heater Assemblies earlier according to PACE Manual and everything looked fine (Heater: ~6ohm, Sensor: >=110ohm). I’ve decided to check them again but on connector plug this time as a last resort. Once again they checked out fine (Pin: 2-5: Heater, Pin: 3-6: Sensor (eevblog-forum-repair-pace-tj70-03.jpg)). I started testing for other pin combinations and Pin 2 (Heater Pin) & Pin 3 (Sensor Pin) were short (~0.08ohm)!I checked other PACE handpieces I’ve (SODR-X-TRACTOR, ThermoPik etc.) but none of them had this weird short between Pin 2 & Pin 3 (PACE uses a universal approach in design and pin layout for all these handpieces with black connectors, heater assemblies are only different as they’re application specific.). I took out the heater assembly from TJ-70 & checked for short between heater and sensor but found none. It was evident now that the short is either on cable/connector or on internal P.C.B. (which houses the connectors for heater assembly and micro-switch for controlling the pump on the station.) of the handpiece. I pulled the guts out of the TJ-70 & sure enough; there were two copper traces, originating from Pin 1 & Pin 2 of the heater assembly connector, which got merged into one midway and got separated again later on the board (eevblog-forum-repair-pace-tj70-04.jpg). I’ve found no reasons for them to get merged (one was from heater, the other one was from sensor) & their appearance was giving me the hint that they got merged due to very little clearance between them (production issue? But PACE has very good quality control; I heard.). So, I’ve gathered up courage to make theses two traces separated on this $$$ TJ-70 handpiece and took out my carving knife. After some careful & delicate effort (and one broken knife blade) they became separated again without damaging the P.C.B. substrate too much. I’ve added a bit of solder on the exposed traces later and cleaned up everything with I.P.A. (eevblog-forum-repair-pace-tj70-05.jpg).Now the moment of truth, connected the partially assembled handpiece to ST-115 again and no OCE this time, everything behaved as normal. I’ve put back everything together and tested it with my MBT-250. It worked on all three channels without any issue, no more blown fuses. PPS-80 too has driven it as usual.My understanding of this relatively bizarre phenomenon is, heater power supply (main transformer may or may not have separate winding for heater, all these handpieces are driven by 21V A.C.; controlled by TRIAC, standard PACE design.) has found out a low impedance return path via sensor circuitry. It was a SHORT for heater power supply; in other words; which was bringing down the power supply in MBT-250 and was the cause of the spurious reset in turn. PPS-80 is probably protected by internal current limiter (or do they have different design? I’m yet to see the service manual.) and survived the short. ST-115 too probably has internal current sense and current limiting system, it could detect the Over-Current condition and protected itself from any damage. Only MBT-250 was without any such protection and has blown the fuse. I’m hoping no damage on the units as the sensor/error amplifiers have very high impedance input and high current won’t flow through them in general (all units are operating in usual manner, fingers crossed!).So, I’ve probably fixed the issue on this TJ-70 handpiece but it left a few questions for me.1. How could PPS-80 drive the faulty unit initially without indicating any errors? (Now I remember; PPS-80 was humming slightly while driving this handpiece in the beginning.)2. Is my TJ-70 a Special-Edition made only for PPS-80 (very unlikely)?3. Was that Trace-Merger intentional? (for stabilizing the sensor loop by using some voodoo which I could not understand.)4. Why does MBT-250 not have any protection (like on ST-115) against such issues?5. PACE has very good Q.C. in place. How this can happen after that? (This handpiece would have failed in initial Q.C. checking, hope they were not using PPS-80 for testing.)6. I said earlier that I’ve scored this PACE Equipment Lot on ebay and the handpiece was brand new. This PACE lot was from a well known Company (edited: I mean to say original owner (probable) of this equipment lot, MITSUBISHI ELECTRIC in this case.). Have they sold it off as part of the lot as it was faulty? (but it was not having any sign of being powered up.)Please let me know what do you think reg. this Curious Case of PACE TJ-70. I know, a lot of community members here use PACE equipment and have valuable insight. It’ll be great if someone can shed light on this P.C.B. issue, someone from PACE here? A photograph of another TJ-70 P.C.B. will be great too (hope I won’t be proven foolish and won’t find the merged tracks there!).

author: Shock
author_rank: Super Contributor
timestamp: June 19, 2019, 11:21:52 pm
content: Quote from: shuvodutta on June 19, 2019, 04:44:52 pmI have the current Intelliheat version of the same TJ-70 handpiece. How old is this specific handpiece? Not sure when the Sensatemp series started as it was some time ago but this handpiece could have been made over 20 years ago.1. Different circuit, the defect caused over current on one station (transformer noise is a indication) on the other it was enough to blow the fuse. Doesn't mean a design problem.2,3. No it had a defect during PCB tining from the looks of it.4. Older design is my guess, and the MBT-250 did have protection.5. Who knows, it was probably a single occurrence.6. I expect it had the heater replaced before the owner gave up. It's not brand new, it's new old stock at best, but I think you can work out why it was never used by the previous owner.Why would Pace sell off a defective handpiece as parts, seems a stupid idea to me. They keep stock of those exact parts, they would figure out what went wrong. If it had been discovered, it would be replaced and corrected in manufacturing, added to QA and QC. This is what companies do to stay in business. It's generally bad business practice purposely letting defects into the ecosystem, so most companies want to avoid it.I don't think there is a conspiracy occurring but good job fixing it. I'm sure you got it for a steal and sometimes great deals come with some extra fun.If anyone was wondering what a TJ-70 ThermoJet is, in a nutshell it's precision hot air handpiece which can be hand or foot actuated. Queue elevator music.

author: Shock
author_rank: Super Contributor
timestamp: June 20, 2019, 01:09:14 am
content: I was just trawling through handpieces on Ebay and found the Sensatemp II TJ-70 version for $100https://www.ebay.com/itm/323787952767Needs a grub screw and some tips. Looks lightly used from the image, not a bad deal for those who don't have one.

author: shuvodutta
author_rank: Contributor
timestamp: June 20, 2019, 05:18:20 am
content: @ShockThank you for your time & the insight you've provided.QuoteThere's no way to find it out but yes, these SensaTemp handpieces with black connectors are not in production any more. (PACE provides excellent support; consumables & spare parts; for these units though.)QuoteThat was my guess too. I also don't think it's a design issue.QuoteFeeling a sigh of relief, thank you.QuoteTrue. What I was trying to convey is that MBT-250 does not indicate (or limit the current) in such scenario like ST-115 does but as you've already said it may be due to older design. MBT-250 user manual says 'Blowing Fuse' is expected behavior in case of 'Heater Short' (PACE MBT-250 User Manual, Page 53, eevblog-forum-repair-pace-tj70-07.jpg).QuoteTrue. PACE build quality is excellent in general. (That's how it compelled me to buy 6 stations & handpieces in last 6 months.)QuoteYou're probably right. That explains how I've received a spare TJ-70 heater in the lot & got the handpiece in virtually unused condition.QuoteI'll make it clear. I was not referring to PACE here.QuoteWhat I've meant to say is, the original owner (probable) of this PACE Equipment Lot I've purchased, MITSUBISHI ELECTRIC in this case. I should have made it clear in the first place. As you've correctly said earlier, they probably got fed up with this unit & decided to sell it off as part of the lot.QuoteNo, no Conspiracy. I don't like any Conspiracy.QuoteYes, you're absolutely right. It's like Pandora's Box. I got 2 PPS-80 with power cords, 1 TJ-70, 1 TT-65, 1 TP-65, 2 bags full of brand new PACE spare parts (including air hose) & consumables for $80 + Free Shipping.QuoteI was also eyeing on this one before I got the deal.

author: Shock
author_rank: Super Contributor
timestamp: June 20, 2019, 05:56:05 am
content: Quote from: shuvodutta on June 20, 2019, 05:18:20 amI was going to mention the manual troubleshooting but I forgot.Quote from: shuvodutta on June 20, 2019, 05:18:20 amAhh. Well actually another well known brand of soldering equipment was guilty a few years back of doing a "tough luck, no warranty" and it was design flaw. Not sure if it was company policy but it looks really bad when that happens. Same with when Dave discovered Weller doesn't use a transformer fuse on some of their stations. Just because it's not written into law doesn't mean you should exclude it heheheh.But yes Pace is big on service and they have to be with industry and government business don't want to nickel and dime big customers.Quote from: shuvodutta on June 20, 2019, 05:18:20 amNice that's like $300 secondhand value of handpieces right there alone. Shows there is some good deals to still be had.Edit:You really have to do your homework and work out what systems those exact handpieces are supported on but you might even be able to come up with a cheap PPS400 PRC2000 style system. I take it you saw this item as wellhttps://www.ebay.com/itm/372689437897MikesRadioRepair on youtube has got seven of them! This one cost $49.95!

author: OwO
author_rank: Super Contributor
timestamp: June 20, 2019, 06:33:06 am
content: I still don't get how a PCB defect like that can slip by, do they not do flying probe testing? Those traces go to SMD pads, so they would be covered by tests. The layout design in general also doesn't look very optimal, with traces going way too close to board edge, something I only see on the crappiest ebay modules. Surely they could have widened the handpiece by just that 1mm and gotten the necessary trace separation?

author: Shock
author_rank: Super Contributor
timestamp: June 20, 2019, 07:07:26 am
content: Quote from: OwO on June 20, 2019, 06:33:06 amLike I said, it could have been assembled like 20 or 30 years ago, who knows how long Sensatemp handpieces have been around for. We can fill several small towns in China with early Chinese capacitor failures PCBs, lets not start jumping to conclusions here on product quality. If it was a real issue it would have been corrected a long time ago.

author: shuvodutta
author_rank: Contributor
timestamp: June 20, 2019, 08:43:10 am
content: @ShockQuoteI think you've started reading my mind reg. PACE equipment.Yes, PPS-400/PRC-2000 system is on my list but I'm yet to be lucky like Mike.True, it takes some time to figure out PACE Station & Handpiece Combination but their documents are well laid and very much helpful. Thanks for the eBay link, I've not checked that earlier.QuoteI watch MikesRadioRepair frequently & seen this video too. (and envied him, do I need to say that?)I would like to mention two other things here which I forgot to mention in last reply.1. Your posts here were really helpful while I was doing my homework on PACE. Thank you.2. Thanks for explaining what TJ-70 ThermoJet is in the first reply, I've completely forgotten doing that.@OwOThanks for joining the discussion. I was also surprised initially but I'm no expert in P.C.B. Design/Manufacturing. That's why I wanted to discuss the issue here, in this forum. As Shock has already described, these handpieces are really old & such issues are extremely rare, might be even single occurence (I've never heard before reg. this issue, neither here nor anywhere else.).

author: shuvodutta
author_rank: Contributor
timestamp: June 20, 2019, 09:23:22 am
content: I've noticed something interesting in the mean time. I've tested this repaired TJ-70 on MBT-250 & ST-115. Set temperature was 400deg. F on both the units (just to test, TJ-70s are advised to be used at 900deg. F.) & test duration was ~15min from a cold start.Both the units have shown ~15deg. F overshoot initially (expected), ST-115 was keeping the idle temperature within +-1deg. F but for MBT-250 it was +-10deg. F. I've tried different channels on MBT-250 but with same result & it could keep my other handpieces within +-1deg. F of the set temperature (within it's stated specs.). Temperature will start dropping on both the stations once hot air stream is switched on & left on for longer time (~2min. in this case.) unless the control loop kicks in but this is expected behavior too; I think.edited: ST-115 has shown ~15deg. F overshoot initially (expected), it was keeping the idle temperature within +-1deg. F. Temperature will start dropping once hot air stream is switched on & left on for longer time (~2min. in this case.) unless the control loop kicks in but this is expected behavior too; I think. However MBT-250 has shown ~60deg. F overshoot & it could keep idle temperature within +-18deg. F. I've tried different channels on MBT-250 but with same result & it could keep my other handpieces within +-2deg. F of the set temperature (within it's stated specs.). It's behavior was interesting with hot air stream left on for longer time, I've described that in later post.I think this has to do something with placement geometry of the temperature sensor (on TJ-70) & control loop response time. MBT-250 & ST-115 probably use different control algorithm (ST-115 is with faster response as being newer among the two.). If someone can test MBT-250 with TJ-70 & share the result, that'll be great.b.t.w. TJ-70 used in this test was without any nozzles.

author: Shock
author_rank: Super Contributor
timestamp: June 20, 2019, 11:34:16 am
content: If it's only 10F that sounds very reasonable, check the power consumption perhaps on different handpieces. Might be load related between handpieces and the MBT250 has some old caps or something.I looked at the PCB on my TJ70 and as expected it's fine. It's obviously a newer revision but just normal traces. They released this version I think in 2005.Interesting pulling it apart, it's fairly easy to disassemble. I wonder on the new Pace Accudrive series since they have the aluminum tweezers coming out (and the aluminum iron already) if they are going to end up making aluminum versions of the actuated handpieces. I expect not, but it's an interesting thought.

author: shuvodutta
author_rank: Contributor
timestamp: June 20, 2019, 03:27:42 pm
content: I've completely forgotten that I use MBT-250 with Centigrade Scale not with Fahrenheit.I've performed the test again (with same initial condition) & updated the initial post with correct data.QuoteThat'll be a good start.QuoteThanks for checking it with your TJ-70. Now it's confirmed that the 'Trace Merger' was not 'by Design'.QuoteYes, their TJ-70 heater replacement manual describes it nicely with exploded view of the handpiece.QuoteYes, we've to wait & see.I've experimented further on this unit & discovered some more interesting result. It's in the next post.

author: Shock
author_rank: Super Contributor
timestamp: June 20, 2019, 03:42:11 pm
content: Might be handy to take a pic at some point to show what exact MBT250 (grey/white/black), and ST115 you have, even the handpieces. There is a few different versions of them, the MBT250 manual lists several, but it should also be on the case somewhere (possibly underside).

author: shuvodutta
author_rank: Contributor
timestamp: June 20, 2019, 03:45:30 pm
content: So, it's time for the next experiment.Set temperature was 400deg. F (with all other test condition same as before.), control loop kicked in at 325deg. F (while hot air stream was on) & brought the temperature back within the set temperature band.I've kept the set temperature at 900deg. F next (with all other test condition same.) & let TJ-70 reach that temperature (MBT-250 kept it within +-14deg. F this time.). Once hot air stream was switched on, temperature started dropping & I was waiting for control loop to get kicked in. I waited up to 410deg. F (dropped from ~900deg. F), it was dropping steadily till then. It started recovering only after I've switched off the hot air stream.My all other actuated PACE handpieces (SX-70, TP-65 etc.) don't show this behavior (their power demand (~45W) is also lesser than TJ-70's (75W).)I think Shock was right. This has something to do with Maximum Power Delivery from the Station & Power Demand from the Handpiece.Any thought on this? Can anyone please repeat the test with their setup?

author: shuvodutta
author_rank: Contributor
timestamp: June 20, 2019, 03:51:10 pm
content: @ShockQuoteYes, I'll do that. In brief, my MBT-250 is with white front panel & black case, ST-115s are all black.

author: Shock
author_rank: Super Contributor
timestamp: June 20, 2019, 04:11:41 pm
content: Another test for power capacity is if the MBT250 has individually powered channels like my MBT350 then you can look for performance dips or power dips running one then two simultaneous handpieces (each time stabilized, then stabilized with air). Check the max wattage obviously which will be somewhere near the model identifier as well. Detective work huh, you should be able to characterize the stations performance though just from observation.If there is an underlying problem with the station, check that the fuse is correctly rated and be prepared to release the magic smoke. Either that or examine the power circuit and do it the safer way.

author: shuvodutta
author_rank: Contributor
timestamp: June 23, 2019, 08:02:50 pm
content: QuoteI was planning for this exactly (did it in a partial manner earlier.) & proceeded immediately after your reply.Equipment/Settings:MBT-250, 185W (100% Duty Cycle, Motor On)Channel 01: TJ-70 (set @900deg. F), 75WChannel 02: SX-70 (set @900deg. F), 48WChannel 03: PS-90 (set @900deg. F), 51WResult:After ~10min. from Cold Start:TJ-70: ~900deg. FSX-70: ~815deg. FPS-90: ~900deg. FPS-90 could operate normally (tested on a heavy copper plane on an old S.M.P.S. P.C.B.) but when the air pump has been actuated from SX-70, MBT-250 rebooted (due to power dip but no blown fuse this time.), tested this incident thrice to be sure. I've reduced PS-90’s set temperature to 400deg. F then & tried switching on the pump again, everything worked this time, no reboot. SX-70 was ~850deg. F, air stream started reducing the temperature & control loop kicked in only after switching off the air stream. SX-70’s set temperature has been changed to 400deg. F, control loop became responsive within 10deg. F of the set temperature. TJ-70 has shown the known behavior, switching on it’s air stream was having no impact on PS-90’s (set to 400deg. F) responsiveness.I planned to post the result earlier but became occupied with another equipment (a sick HP 6623A, suffering from heavy transit damage, more on it will be in another thread.).It'll be great to hear from any other forum members with this Equipment/Handpiece Combination.QuoteThanks for your advice, I was ready for Magic Smoke this time but none came.

author: PACE-Worldwide
author_rank: Regular Contributor
timestamp: June 23, 2019, 11:04:43 pm
content: Hi shuvodutta,Congrats on your great ebay buy! It looks like It looks like you’ve got the situation well in hand, but I’d like to make a few comments concerning the TJ-70 and other units you purchased:The PPS-80 (also known as the MBT 201 Analog Soldering/Desoldering Station) you bought is probably close to 20 years old, since we have not manufactured that unit since around the turn of the century. The MBT250 could also be very old as we have manufactured that series since 1990 (and still do)! You may want to check the heater of each handpiece as each heater should display a date code as to when it was manufactured. That will give you a better idea as to the age of each handpiece (ore at least the heater assembly). The PPS-80 and PPS985 (MBT250 Power Supply) should also have a date code bulit into the serial number ... I think it's a Julian date.We’re still selling the SensaTemp, Black Connector version of the TJ-70 ThermoJet Hot Air/Convective Handpiece PN 7023-0002-P1, which is compatible with older PACE Power Supplies such as the PPS-80/MBT201 , PPS-85/MBT250 series and PPS-400/PRC2000 series. It can be found here:https://www.paceworldwide.com/products/handpieces/air-pencils/tj70-thermojet-hot-airconvective-handpiece-sensatemp-black.We also have an IntellHeat version of the TJ-70, which works with newer PACE systems like the MBT301 or MBT350. The only difference between the IntelliHeat and SensaTemp versions is the pin configuration of the black connector (SensaTemp) vs the blue connector (IntelliHeat). Both TJ-70s are otherwise identical.Good call on the “weird short between Pin 2 & Pin 3” on the handpiece pcb … this is definitely NOT normal. I suspect this is a defect that occurred long ago, and I would bet this caused a host of failures in other MBT250’s of the day. I have no clue as to why the TJ-70 would work on a PPS-80/MBT201 without indicating any errors but not the PPS-85/MBT250. Maybe something to do with the more complicated firmware of the digital MBT250 versus the analog/dial operated MBT201? As you mentioned, weird.Is my TJ-70 a Special-Edition made only for PPS-80 (very unlikely)?Your TJ-70 was definitely not a special edition made for the PPS-80/MBT201. All SensaTemp handpieces (and IntelliHeat handpieces for that matter) are designed to be compatible with a wide range of PACE Power Supplies, whether old or new. The first SensaTemp Power Supply we ever produced (called the MBT-210, discontinued in 1989)will still workwithanySensaTemp handpiece, including modern SX-100 Sodr-X-Tractor, PS-90 Soldering Iron, TT-65 ThermoTweez, TP-65 ThermoPik and TJ-70!Was that Trace-Merger intentional?Probably not, but I can check with one of our design engineers to see if this was the case. One of the guys here has work at PACE since the late 80s, and he may remember this design. My feeling is it was a anomalous set of pc boards that were produced in the 90's that accidentally were manufactured and distributed. Probably caused great problems/consternation among MBT250 users.Why does MBT-250 not have any protection (like on ST-115) against such issues?I have no clue ... I'll ask.PACE has very good Q.C. in place. How this can happen after that? (This handpiece would have failed in initial Q.C. checking, hope they were not using PPS-80 for testing.)On SensaTemp handpieces, we test a only certain percentage of the handpieces before going out. This is because the designs have proven to be quite solid and ultra-reliable after hundreds of thousands of use in military depots, production rework centers and the like. On newer products, like our ADS200 Tip Heater Cartridges, we 100% test them before they go out.In brief, my MBT-250 is with white front panel & black case, ST-115s are all black.It’s hard to tell exactly which MBT250 version you have, as we have change the color scheme of that unit several times. The ST-115 you own is definitely an older one, as all black-cased ST-115s are SensaTemp versions, last produced in early 2000's, while the current ST-115 (looks the same, except the case is clear anodized) is an IntelliHeat-compatible unit that started production in 2003/2004.I have some other comments but I place them in another entry later on.Thanks for the comments!Aaron

author: PACE-Worldwide
author_rank: Regular Contributor
timestamp: June 24, 2019, 12:04:09 am
content: Quote from: shuvodutta on June 20, 2019, 09:23:22 amshuvodutta,Let me discuss the idiosyncrasies of the TJ-70 ThermoJet Hot Air/Convective Handpiece. The TJ-70 was designed around 1991, mainly to remove small chip capacitors on double-sided pcb's, solder QFP's onto surface mount boards using solder paste/hot air, to heat-shrink tubing, or to help remove conformal coatings on pcb's (you overcure epoxies and soften urethane coatings by using the hot air). But with modern electronic assemblies that use lead-free solder, multilayer boards and materials designed to dissipate heat, I will admit that it is grossly under-powered. Let's face it, there is only so much heat you can produce with a 75 Watt/21 VAC hot air pencil. Because of this low wattage, the TJ-70's performance and temperature accuracy is going to be slightly different than other PACE SensaTemp handpieces. If you look for a comparison with competitive units, the Quick 861DW is a line-voltage unit with 1000Watts at its disposal. They definitely have the heat generating capacity as that is exactly what is was designed to do.We recommend a temperature of 900°F for a reason: the heater can barely reach solder melt temperatures at lower temperatures. While the TJ-70 uses the same super-accurate laser-trimmed, platinum RTD sensor as other SensaTemp handpieces, the placement of the sensor is much further away from the end of the heater. This is intentional, to "trick" the heater into performing better. Thus, when you set a temperature of 900°F, the heater may keep pumping power into the heater ... it may actually reach temperatures of 950°F at the front of the heater since the sensor is so far from the front. The result: you get higher temperature hot air generated, but wider swings of temperature including overshooting. A PS-90 soldering iron or the SX-100 Desoldering Iron will not perform this way and are usually dead-nuts accurate. You set the temperature to 700°F, and you get 700°F at the end of those tips, maybe 6°F difference between sensor and end of tip.Related to this, the MBT250 has 3 independent channels/outputs that have the capability to handle any combination of 3 compatible handpieces. But each channel is restricted to 80 watts maximum, up to 185 Watts overall. Actuating the motor pump also will affect the power, as it takes approximately 20+ Watts to run the pump. So when you use 3 handpieces simultaneously, plus actuate the pump, which you will during desoldering or hot air generation, you might be bumping up against it's maximum power rating, especially when you first turn the power supply on (all handpieces run at 100% wattage when initially turned on).Hopefully, this will explain some of your temperature fluctuations and blown fuses.Cheers,Aaron

author: shuvodutta
author_rank: Contributor
timestamp: June 24, 2019, 06:55:33 pm
content: Thank you Aaron for joining the discussion & the valuable insight you've provided. I hope this thread will be helpful to anyone with such issues in future.QuoteMy TJ-70 is from 2002 & PPS-80 is from 2001 (Thanks for the clue.).QuoteYou've confirmed my assumption reg. placement of the temperature sensor. I was surprised to see that ST-115 could still keep the temperature of TJ-70 within +-1deg. F of the set temperature. But that was probably due to being newer than MBT-250 (different control algorithm, different software polling time for the temperature sensor etc.) as I've said earlier.QuoteThis falls in line with the result of little experiment I've performed.Please let us know if you could get any further information on the TJ-70 issue or reg. the design of PPS-80/MBT-250/ST-115.PACE build quality & support for the existing product line is really great, it impressed me to the point that I took all the hassles for importing these units along with other consumables (it was for my personal use & none of the PACE distributors in my country keeps ready stock!).Thank you again.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 25, 2019, 06:23:27 am
content: Quote from: Shock on June 20, 2019, 07:07:26 amFaults on devices from prestiigious companies are, alas, not rare.In one job, where we made mining industry simulators, we received a shipment of "multipurpose switch" assemblies (the ones that are mounted on the vehicle steering column to operate lights, horns, etc), from a prominent manufacturer of the real equipment we were simulating.Around 30% of these switches were faulty!At another job, an Icom IC 910 transceiver was overheating on test, producing low power, & "making a funny clicking sound".Fault was a ribbon cable fouling the cooling fan.The cable was tied back out of the way, & all was well!

author: p514
author_rank: Newbie
timestamp: June 25, 2019, 12:06:22 pm
content: Quote from: PACE-Worldwide on June 24, 2019, 12:04:09 amAre the characteristics of the TJ-85 different from the TJ-70?

author: tooki
author_rank: Super Contributor
timestamp: June 25, 2019, 04:56:03 pm
content: PaceCustomer:I have some questions...Pace:I talked to the engineers who designed it and here’s the answers and they updated the ROM to make it better. Here’s a new ROM chip and IC puller in the mail.Other companiesCustomer:I have some questions...Company:[replies in corporate]

author: shuvodutta
author_rank: Contributor
timestamp: July 02, 2019, 06:53:14 pm
content: @vk6zgoThanks for joining the discussion. Your insight was interesting.@p514Thanks for joining the discussion.QuoteApplication wise they look similar. TJ-85 is designed to be used with IntelliHeat Systems but it's a Precision Hot Air Tool like TJ-70 & does not have much power at it's disposal (51W; according to PACE Documents. Few of the TJ-85 Documents are actually from TJ-70!). Aaron will be able to answer in more details.@tookiThanks for joining the discussion.QuoteYou've nailed it!