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DIY mini T2 Build Thread


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I got the quick based on a review my lewis rossmann on you tube who does apple mac repairs

. I tend to be paranoid, so I assume solder paste will go under components and cause shorts... I plan to get some experience just dropping the components on the raw solder paste and applying heat, but I did not want to take the risk with the mini t2. My general philosophy is find something that works and then optimise it. there is one issue with my smd method... if you apply heat with the soldering iron for too long you burn off all the flux in the solder. So, a quick wipe with the iron is all that’s needed to get the solder to solidify on the pads. secondly any solder on the iron tip has no flux left so you should not apply the soldering iron to a pad that has no solder paste on it, otherwise the solder that will stick to the pad from the iron tip will have zero flux.

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Half a year ago I promised to build a new original DIY T2. Now it’s done. After some difficulties with left channel and PSU she is playing as an original DIY T2 does!!! Thinking of retire a

A few points regarding the boards Michael have had made on my gerbers. They are basically the same as my kitchen made boards I made  five months ago. The small tube footprint has no hole for the

I used two transformers.  both with electromagnetic shields, static shields and potted from http://www.mueller-rondo.com/kontakt.htm . (The low voltage transformer can be used for the blue hawaii

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On 3/5/2020 at 3:07 PM, jose said:

Pars, for $ 40 that gossip is worth it:

Central leg of HN4A51J a second after solder.

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OPA197

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Edit. Since I did my F5HA with SMD I´m use this JBC Flux It is probably not the best in the world but it works for me.

 

 

 

 

 

Well, it was $48 shipped, but got it the other day. Still figuring out how to use it. Here is an ARM processor, LQFP-100 package, soldered in. I had the alignment perfect; it moved slightly when I was tacking down a couple of corner pins. I'll go thru and verify with my Fluke.

744460117_Untitled6.thumb.png.93a73444c05ce1cd511900ced0ea3e71.png

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On 2/14/2020 at 7:09 PM, jamesmking said:

SMD soldering was done in a three step process.

.....Hold the component with twisers onto the pads and with my other hand use a Quick 861DA hot air station using the smallest supplied nozzle with airflow setting all the way down to 5 (even then its possible to send one of the small diodes into orbit with that air flow)...  to reflow the solder onto the component.

 

OK, I'm trying and hopefully learning something, with solder paste and component in place and then hot air.

What temperature and airflow did you use? Also what type of solder paste?

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joamat: on the quick air flow 5 out of 120 !!! even then you can orbit small diodes if you release the tweezers before the solder has melted the quick is powerful, 120 will almost remove through hole comonents and your third arm.... maybe thats why mwl168 only has 2 hands....

temperature 330C to 360C depending upon ground plane, size of component.

solder paste nothing special off ebay  its MECHANIC XG-Z40 Liquid Solder Soldering Paste 10cc has a good amount of flux in it seems to work quite well for my soldering technique but then I have not tried any other paste....

mwl168: you DON'T have 3 hands?😕

My smd soldering  method requires 2, left hand holding the twessers, right hand holding the hot air nozzle.... 

 

Edited by jamesmking
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Thanks. Now I’ve done some more practice. First solder with leaded solder and then with lead free. Guess I prefer leaded as it’s faster and a bit easier. Trying different settings. 300C and air flow at 5 seems to work with small parts and leaded paste.

 

I can do it all with one hand. 1; solder paste on pads. 2; put component with tweezer on pasted pads. 3; blow hot air till paste melts and sucks component nicely in place on pads. Only right hand is needed. One hand left for... a good cigarr…

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I’m building a Controleo3 based re-flow oven for the SMD soldering until I get more experience on test boards with hand soldering SMD components. It should leave both hands free😊. Just waiting on the toaster oven to arrive on Saturday to start modifying it. 

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6 hours ago, Oneguy said:

I’m building a Controleo3 based re-flow oven for the SMD soldering until I get more experience on test boards with hand soldering SMD components. It should leave both hands free😊. Just waiting on the toaster oven to arrive on Saturday to start modifying it. 

OneGuy: "both hands free"?.... you also only have two hands? 

but can the reflow oven do double sided?

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1 hour ago, jamesmking said:

OneGuy: "both hands free"?.... you also only have two hands? 

but can the reflow oven do double sided?

Well not “both hands free” during the entire process. You still have to apply paste and place the component but the actual soldering portion is hands free.

There are some methods out there for tackling double sided boards but I haven’t looked into them. Here a few:

https://forum.allaboutcircuits.com/threads/how-are-double-sided-pcbs-soldered-in-a-reflow-oven.55282/

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I guess most of the parts on underside will stay in place by surface tension. If they fall down don’t blame me – put blame on Newton. Anyhow, I held pcb upside-down and blow 360C at flow 5 for five minutes and 0805 resistors and HN4A51J stayed put while solder was liquid so I could move them off with a tweezer.

For me the most difficult is to put the right amount paste on pads, it easily become very messy…

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Now printed stencil 0.2 mm thick and I don’t think it will work, not with my printer anyway, a Prusa i3. Printer has big difficulties with small footprints as so-23 and sot-26. The others might work… maybe, not sure. Also the side towards pcb is to rough.

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  • 2 weeks later...

Now when Kerry regulators and psu board are on its way I and maybe a few other builders wonder what transformers might be appropriate.

James, @jamesmking, what transformers did you acquired for your mini T2?

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I used two transformers.  both with electromagnetic shields, static shields and potted from http://www.mueller-rondo.com/kontakt.htm .

(The low voltage transformer can be used for the blue hawaii  -  the 6922 windings are just not used the other voltages and currents are fine.)

low voltage: transformer

  • two windings 6.3V 4.5A for EL34 heaters one winding for each channel NOTE these windings are -400VDC to ground 
  • two windings 6.3V 1.5A for 6992 heaters one for each channel and my HT delay board
  • two windings 15.5V 0.4A for golden reference LV board + and - 15VDC

high voltage transformer 

  • one winding 365V 0.2A for  dual golden reference HV board -460VDC. NOTE 365VAC gives 516VDC which gives less than 10% margin before reaching the 550V limit of most high voltage 550V 470uF input caps on the golden reference HV...  so be careful if your household mains voltages are usually higher than spec.
  • one winding 322V 0.2A for dual golden reference HV board  +400VDC and +580V stax bias
  • one winding 192V 0.18A for golden reference HV board +220VDC

The blue hawaii just fits in a single 2u case 400mm deep, using 1 transformer with less windings - one less high voltage and two less 6.3V, golden reference LV board and golden reference HV board.

The mini T2 has two transformers AND an extra HV board so the issue is not height but depth,

to give you a size idea the transformers are

Low voltage diameter 105mm height 55mm

High voltage diameter 115mm height 65mm

not having shields in the transformers will result in some hum and electrical interference if you turn the volume all the way up if you go single case. Not potting the transformers might make them a little smaller. putting the transformers into a separate case makes both the blue hawaii and mini t2 absolutely silent.

you cant easily use the space bellow the mini t2 amp boards because they have 4 pillars which screw into the bottom of the case so you don't bend the amp boards when inserting or removing the valves. Neither the golden reference LV or HV boards will fit bellow the am boards because of this.

for both my blue hawaii and mini t2 builds I went with the following case  https://modushop.biz/site/index.php?route=product/product&path=102&product_id=195  its 2u, 400mm deep and has large heat sinking and is fully aluminium so fairly easy to drill. The heat sinking is overkill for the mini t2 - which runs quite cool, but the blue hawaii needs those large heat sinks, 

For the umbilical chord I used 1KV silicon rubber multi-strand copper hookup wires (https://www.mouser.co.uk/Search/Refine?Keyword=CT2956) for good flexibility and Russian 19 pin military connectors (https://www.ebay.co.uk/itm/19-pin-Soviet-Military-connector-Female-Male-Set-Oty-1/254196620095?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649).  I then covered the bundle with expandable nylon braid and tested the leads with an insulation tester and they passed 5 minutes at 2500V with 20+Gohm resistance. They failed insulation at 5KV.

P.S. if you build golden reference HV boards kemet do 550V 470uF caps which are 65mm high and will fit in a 2u case https://www.mouser.co.uk/Passive-Components/_/N-5g73Z1yzvvqx?Keyword=kemet+550V+470uF&FS=True.  Be careful Kemet also sell 680uF 550V caps that are 80mm high and will need a 3u case to fit . (https://www.mouser.co.uk/ProductDetail/KEMET/ALC10A681EL550?qs=%2Fha2pyFadug678O2NPlQ%2F8WMW0dBZWV2y30oREQu6XgezeenvV90cA%3D%3D).  for the +220VDC golden ref board you can save some money and go kemet 470uf 450V or even 400V. I didnt simply because I might re-purpose the 220V board to a higher voltage sometime.But the 550v 470uF kemet caps are not cheap.

P.S. the golden reference LV board is not necessary, only the servos are run from the + and - 15V lines so you could just populate the low voltage section of the GRHV board. However, if you don't want thumps on switch-off the + and -12V lines require large capacitors so the servos stay powered while the HV lines fade.  I found ~15000uF to 22000uF is required but these caps are physically too large to fit in the simple LV section of the GRHV board. They fit fine in the GRLV board, but a full GRLV board is extra expense just to avoid switch off thump. I use GRLV boards in lots of projects so again they can be repurposed...

 

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  • 1 month later...

No a good day… OP27 next to VOL618A on fire of both channels and GRHV negative rail dead too. I thought that in this board version that I have this problem was corrected ... I was wrong. I hope I just screwed up the OP27 and not the rest of the sand.

Positive, I was able to see that all the LEDs were on. 

It will take a long time to desolder everything.

 

 

 

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Do not worry.

Yes, almost immediately: the right channel burned and then the left channel plus the negative rail of the GRHV.

The amplifier had been in "stand-by" for 5 minutes, heating the heating filaments before applying voltage.

At the moment I have cleaned the damage on my PSU;

I have verified that the low voltage source has also passed to a better life...  although it is already ready again (news LM7X15). I suppose that when the OPA was short-circuited it took the LM ahead.

I have cleaned the GRHV negative rail board and will install it tonight.

About the amp: I still have to check for damage.
Both LEDs were on when everything happened. I hope the damages are only reduced to the part of the OPA27. Any suggestions on possible collateral damage?

My idea is to remove all parts of that servo and run the amp without it or using the servo on top. I understand that it is possible.

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I have run the amp without the balance servo, just by carefully adjusting the trimmer, but the opto coupler is connected to the dc  offset (i.e. make the average of the + and -  audio signals 0v with respect to ground) not the balance  servo (which makes the average of the + and - audio signals 0v with respect to each other only.

also check the valves/tubes if you have a tester...  I have found the 6922s to be a bit fragile and the el34s have -400V on their heaters so if the negative 560V rail has gone crazy there could be heater to cathode leakage...

do you have a variac? I always bring my new builds up to full voltage slowly... My amp has two transformers one for the heaters and +-15v and one for the high voltages. I connected the low voltage transformer directly to the mains and only connected the hv transformer to the variac.

What resistors did you use? I used vishay crcw1206 which are rated at 200v and crcw0805 for the 1/8w which are rated at 150v., they were the highest rated voltages I could find on mouser for 100ppm 1%...

I have a dca75 from peak electronics, https://www.peakelec.co.uk/acatalog/dca75-dca-pro-semiconductor-analyser.html#SID=24 its been very useful for post mortem checking (if I de-solder a transistor I can compare the dca75 measurement with a spare transistor of the same type. I often find failed transistors simply show up as dual back to back diodes or dead shorts. Note the DCA does have trouble identifying 10m90s and similar). I have even found some fake transistors using it. Its not designed for in circuit testing, but it can be use in circuit for comparisons between transistors in the left and right amp boards. If you have not got a dca75 I highly recommend it. You can also get an adaptor for sot23 https://www.peakelec.co.uk/acatalog/pca23-peak-component-adapter-sot23.html and I found an adapter on ebay for sot23-6,  https://www.ebay.co.uk/itm/SOT23-SOT23-6-SOT23-6L-IC-Testsockel-Programmieradapter-Einbrennsockel-F3I4/383314954496?hash=item593f5a0900:g:dWoAAOSwTYZd8frU so I can test dual smd transistors too.

I also created a little op amp test circuit on a bread board, unity gain just so that I could power it and feed in a test signal and scope the output, I got a adaptor for 8 pin smd from ebay https://www.ebay.co.uk/itm/SMD-SO8-SOP8-SOIC8-DIP8-2-54mm-DIP8-Programmier-Adapter-SMD-Sockel-150mil/252912033731?hash=item3ae2bb5fc3:g:yKcAAOSwmE9b-JqP

so I could also test smd opamps.... I love having lots of test jigs. Good luck with your troubleshooting and repairs.

 

 

Edited by jamesmking
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Yes, I used Vishay crcw0805 and crcw1206 too. Luckily the tubes are correct.

Due to the somewhat peculiar configuration of this amplifier I have skipped my procedure for turning on. 

 

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