Switching 100V Japanese TA-N86 for 220V AC

It was a long time since I decided to publish this article. Now I am ready.

First of all some facts below:

  1. TA-N86 was available in 100/120V (US, Canadian, JDM) and 220/240V (UK, AEP) versions, where 220V was only TA-N86B (black anodized faceplate) version.
  2. Power supply is 20kHz SMPS (switching-mode power supply)
  3. Japan domestic market (JDM) versions were only silver faceplate and (very important) has undergone the “second revision” to the original version at the very late years of production with certain improvements in circuitry and parts quality. Hence most updated “Rev. 2″ of TA-N86 was only available in Japan. It is clearly distinguishable by binding posts  - big and round with screw cap, even able to accept banana terminals in some cases.
  4. Service manual is widely available and contain both SMPS schematics – 100V and 220V all together, so the difference is clearly described (however with some typos). I made hi-quality scan of the original Service Manual here. But everything is not that easy.
  5. It is  about 30 parts total to change, so the task will require some advanced level of technical knowledge and sophisticated civil electronics understanding. Good quality soldering/desoldering equipment is a must.
  6. Some BJTs required for replacement are not available with current product lines (which are very few, but still quite sensible) – so some access to the old stock has to be definitely considered.
  7. The most problematic part is the high frequency transformer. It will require full replacement or (!) primary winding extension.
WARNING!!! all primary SPMS circuits are live wiring!!! The risk of high voltage (over 400V) power injure which may result in significant health harm or even death. Please be extremely careful while assembling, disassembling or measurements.

OK lets start.

Lets look into schematics.

What we see is the circuit of US and Canadian model (similar to JDM, absolutely no difference) and AEP/UK 220V version. The circuit does utilize some old design, using simple rectification (input AC goes to rectification diodes bridge), power regulator (which can go switching though), error amplifier managing the regulator output, invertor and its oscillating circuit. Secondary part of SPMS is pretty obvious – secondary  trafo winding – selectable by relay for class A or class B voltage rails adjustment – being rectifying by normal diode bridge followed by LC-filter applied for smoothing voltage surge.

OK, I made a list of parts to replace. Better to have it printed out before you start:

Well, now we go on. Step by step guide is below:

Staring with initial picture:

This is how original 110V PSU looks like. Invertor transistor are on the back side.

So, given the above schematics, remove all those parts to correspond 220V PSU schematics. Actually – that’s almost everything BEFORE primary winding of the high frequency transformer. Also remove four invertor BJTs on the soldering side.

TA-N86 PSU consists of four general blocks – input regulator (with switching capability), impulse generator (starting circuit), invertor and secondary circuits. So switching actually is all replacing input regulator in full followed by replacing several supply chains to the staring circuit and feedback. Plus four invertor transistors for sure, as they operate almost on double voltage.

Main trick is actually to solder in all new parts for input regulator and to CUT OFF the trace feeding invertor (blue cross on the picture above).

 

WARNING!!!! ALL PSU CIRCUITS before transformer has it all proper power rails which is totally irrelevant to the amp. Special care to the equipment – all primary PSU rails are hot wire with voltages up to 400V, i.e. grounded scope connected directly to negative rail will be blown most probably, as well as PSU. So if using any equipment connected to wall socket should be powered ONLY throgh isolation transformer.

 

OK, fist things first. After input regulator soldered in, check voltage at positive rail (L604 output). Should be about 280V given that primary rectified voltage is 310V DC. Positive rail voltage should be adjustable by RT601. If you have >300V DC instead of 280V then Q613 and/or Q601 are out.

Replace other parts, including invertor. One o the tricks here is the differential amp Q605/606: three resistors which are R609, R607 and R606 replaced by 100k value. This have to have 1% tolerance or less (better). Measure all three by hand and choose only those having the lowest possible difference.

Once regulator is started and working properly, lets focus on HF transformer. Apparently, PSU is PWM-based, but I still not understand how to adjust pulse width. So I use to add some turns to the primary winding and this is real challenge  - the transformer in newer TA-N86 Japanese-only  modifications  (with screw speaker terminals) is made of foil, which is really cool. Moreover transformer is sectioned. Primary winding is sectioned into two parts = 18 turns + 18 turns, connected by thermal breaker. Given that double voltage is applied, we need to double the turns, i.e. to have 64 turns instead of 32. The best way ( best works for me in terms of mechanical convenience) to wind-off secondary section of primary winding  - that’s the most outer portion down to the termal breaker connection and solder new wire right to the breaker, adding 64-18=46 turns (I make 50 turns, just to have more adjustment capacity). This is about 5,5 meters long of 0.8mm enamel wire. Use epoxy and thermal scotch tape to fix the new section. Check primary winding with ohmmeter and inductance meter, both should be double to the original values.

 

After tranny is fixed, solder it back, put solder joint on positive rail previously cut (restore blue cross), so to start invertor. Put 100W bulb to the output rectifier. Cross fingers and turn on. Thing is pretty simple and should start with no problem.

DO NOT forget to replace big black capacitor on the main board to 400V value!!!

 

Pictures of the modified 110-220V PSU will be posted shortly.

 

(c) oldhifi.su, June 2016.

 

 

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