Thorens TD-115 and the repairer with two left hands…

I’m working on a TD-115 that belongs to friend Richard. It was pretty hammered, looked like it had been living in a shed for years. I’ve stripped it down, cleaned every contact, lubricated everything that moves and tested most of the components on the circuit boards. It’s strangely constructed, I read it described as being ‘high tech done cheap’. I don’t think it’s highly rated among Thorens enthusiasts, but I’ll finish it and get it running – why not?

The foam in the suspension ‘pods’ had rotted away, well, crystallised would be a better description. I cleaned it all out and looked for new foam inserts on ebay, but there were none that I could find. I made some today – I marked out circles on a piece of quite thick foam – my friend Mike had thought thicker (and denser) was better, and any foam was better than no foam – and cut it using a foam cutter I constructed from plywood, nichrome wire and hot-melt glue. I powered it with my DC supply – 1.2A, 2.8V produced about 100 degrees according to my multimeter’s thermocouple. Cut the foam into discs, made holes in the centres with a craft knife and reassembled the pods. Seems OK!

Here are some pictures of the shemozzle. As I’ve said about other projects, if I can do it, you can!

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Today I realised, while trying to cut replacement temple pads for my Koss TNT/77 headphones, that the wire needs to be under tension to make an even cut, so I rigged up a clothes peg spring to provide same. It’s probably unnecessarily complicated, but I feel quite proud…here are some pics:

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Also added banana plugs to make hooking it up to the power supply easier. It sounds like a koto or banjo if you pluck the string!

So the next thing I did wrong…broke the bobbles off the ends of the stupid plastic speed selector linkage rods. I really don’t get the way they’ve designed this thing! I reconstructed them with JB Weld, plastic tubes from Q-tips and new bobbles from an old style of cable tie that I’d saved. I didn’t expect it to work, but it did! You can see the linkages in the picture below. Friend Mike used to work at the Thorens importer years ago and said the linkages were a popular part – “Technicians were always breaking them”. Glad it’s not just me…I suppose I should have bought replacements from ebay, and I looked, but the only two listings  which contained the parts didn’t have all the linkages, had a lot of other parts I didn’t need and would have been reasonably expensive, so I just made some new ones up. Tsk.

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I’m on the final stretch with this, but it’s a long stretch: today I spent two hours or so reassembling it. I realised there are adjuster pieces on the ends of each suspension pod, so levelled them and took the opportunity to tighten and Loctite all the nuts in the pods themselves. I got the turntable running, adjusted the speed control pots (the cutouts on the top edge of the platter are for 33rpm, the ones on the bottom edge 45rpm) but there were some grinding noises as the platter revolved. I realised the height of the bearing housing can actually be adjusted – there’s a circular spring-steel washer that sits underneath it, and the three screws holding the housing in place can be adjusted, and the spring tensions the housing against them. I used my Vernier calipers to set them to about 5mm and all the grinding stopped. I’ll Loctite the screws in place. The arm lifter doesn’t work properly, but I found that if I lifted the arm and swung it inboard of the label edge, the platter stopped. The service manual has instructions for setting the auto-stop so I’ll follow them – tomorrow!

Auto-stop set: I just undid the securing screw and moved the shutter until the arm lifted at the appropriate point in the lead-out groove. THEN…I tested continuity from the audio plugs to the cartridge pins: none in the right channel. I isolated the problem to the connector the arm wand plugs into. Oh, great: I’ll have to remove the tonearm to access it! I just unscrewed the cups the arm pivots up and down in, then removed the top cup in which the arm pivots laterally. I unsoldered the tonearm wires from the terminal board under the arm and removed the tonearm base. A screw held the shaft in place, I removed it, removed the shaft then tapped the connector out with a small drift. I soldered new wires to the connector pins, heatshrunk each connection and reassembled the connector. I’m not making this very clear, but you’ll see what I mean from the photo.

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Each pin has a small spring around it so when the arm wand is installed, the pin retracts and is held against the contact pad in the wand by spring tension. Soldering wires to the pins (they had originally been crimped) heated the pins (even though I clamped them in an alligator clip as a heat shunt), must have melted the plastic slightly and made the pins move less freely in their holes. I tried freeing them up with contact cleaner and tweezers, but with limited success. However, when I reassembled the arm there was continuity all the way from the cartridge to the ends of the tonearm wires, phew!

So, on the home stretch (I know I’ve said this before!) – acrylic cement arrived, I glued the crack in the dustcover and fitted a small aluminium plate at the rear of the cover to reinforce the repair. Did some more polishing and waxed the plinth. I found that the arm wasn’t lifting very high at the end of the side, so I shortened and reformed the spring responsible for that. Had to have another go at setting the auto-stop shutter, but finally everything is working as it should. I’ll listen to a record tomorrow, take some photos and list it. I think this has taken me about a month, off and on. Quite a project!

Abiding impressions of this turntable: ambitious, convoluted design which has been cheaply realised. Takes an absolute age to set everything up. I doubt that this could hold its own against any of the Japanese turntables of the same era and price point. Why didn’t Thorens stick to making high-end ‘tables? Actually, I take that back – the TD-280 is an underrated deck. Very simple, well-executed. THAT’S the one to buy if you’re on a budget and absolutely must have a Thorens (IMHO).

Kenwood KA-400

I’m fixing this for my friend Malin’s Dad. He’d said it had a crackle in the left channel, and when I’d tested it there was no crackle. I lubed all the pots, brushed out the dust and checked the idling current, then put it back together.  On Friday night I hooked it up to a turntable and some speakers, and there was the crackle. Turns out it was just in the phono channel. I looked at the schematic and found the phono channel had two Hitachi HA1457 opamps, which are apparently notorious for going noisy over time. I opened the amp up, tested all the other components in the left phono channel (they were fine) then swapped the HA1457s left-to-right. The crackle didn’t move – it went away! It may come back, but maybe the problem was dry solder joints. The joints looked fine on the surface, but some of them seemed a little bit crystalline when I desoldered them. Who knows? Maybe the opamp was just  bored and making trouble.

iPhone 5S Logic Board Repair

So, inspired by the Jessa Jones videos I’ve been watching, I bought an Amscope SE-400X microscope on ebay. It’s a basic ‘scope, but seems pretty incredible to me. I probably should have bought the model with the gooseneck LED light, but the little tungsten bulb on my one seems perfectly adequate. I tried a few things on some dead logic boards (read ‘destroyed  them’) and after a bit of practice I did my first board repair the other day. I’d damaged the FPC digitiser connector on an iPhone 5S plugging and unplugging screens. I bought some replacement connectors on ebay, removed the broken connector (basically melted it off) without taking any pads with it, tinned the pads and soldered on a new connector. It was extremely nerve-wracking! There were certain pads that, no matter how much flux I put on or how many times I tried, I couldn’t solder them. I guess they were earth pads, and I was contending with thermal mass. After soldering I tried each pad with tweezers and just kept going ’til they were all done. I’d bought a Hakko T18-BR02 tip for my iron, it’s very fine with a bend. Despite using flux, I found the solder would blob on the end rather than adhere to the pins. I’ve ordered some 0.5mm solder (current solder is 0.71mm) so we’ll see if that makes a difference. It may of course just be my technique! I tinned the tip as it was heating up, and have used Goot tip refresher and the wire cleaner, so hopefully all the conditions were right. I reassembled the phone today and the touch worked perfectly. Nobody was more surprised than me! However, I managed to damage the replacement screen and knock out the backlight. D’oh! But…success on the micro-soldering front. It was funny, half way through soldering the connector I took a break, found a dead logic board and soldered a connector to it for practice. It went much smoother than the one I was working on!

So, watching plenty of YouTube videos, a decent entry-level microscope, appropriate soldering tip, some practice, and it went OK for a first time. I’m sure there was some ‘beginner’s luck’ at work, but it’s encouraging. And I’m 56 with poor eyesight and shaky hands. If I can do it, you can do it.

 

Skytec/QTX SP1200A 170.313 Powered Speaker. Blown Output IC – what is it?

My friend Mike has three of these with blown output ICs. Unfortunately there’s no part number printed on the IC, so (not being internet savvy) he asked me to search for a schematic. I couldn’t find anything, but a couple of nights ago was looking around and found the website of the Dutch distributor for these speakers, Tronios BV:

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There was a field for asking questions, which I did, and next day I got a request from them for a photo of the IC, which I sent today. About three minutes later I got an email from a Tronios employee, Ties Oude Geerdink, telling me the IC was a TDA7294.

It amazes me that, in this age of cut-throat commercialism, there are business people who will help others even when there’s no money in it for them. So, thanks to Ties, my friend Mike can now repair his speakers. Three less things for the landfill!

Hitachi HT-65S Turntable

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Hmmm…this has the classic stiff auto-return trip lever symptom of the arm moving to the start of the record and then immediately returning to the armrest. If only it were so simple…in many cases a drop of oil fixes this problem, but this is a fairly complicated fully automatic mechanism. A motor drives a cam with a two-way lever which cues the arm and then returns it at the end of the side. There’s also an LED/light dependent resistor arrangement that senses the location of the arm. I pulled the mechanism to bits – it’s made of nylon or delrin, and is held together with clips that can easily be released. I cleaned off old grease and replaced it with Superlube grease, and found a slightly less stretched belt for the motor. Back together it worked properly, and I thought the job was done. But the next morning it was at its old tricks. I repeated this process a few more times, and eventually I started thinking it was an electronic, not mechanical, problem. I checked the LED and LDRs, the latter by hooking up my meter, set on Ohms, then shining a light on the resistor. The resistance dropped from megOhms to low kOhms, so I assumed the LDRs were behaving as they should. I tested transistors and capacitors, everything seemed OK so powered the TT up and it worked properly, but next morning was faulty again. I thought the motor control IC, BA6134, might be malfunctioning, but there’s virtually nothing of any use about it on the internet – I think it was a Hitachi-only IC, manufactured by Rohm. So, unobtanium. I actually made the problem worse with my tinkering – instead of just returning, the mechanism began cycling through lift/lower constantly. It seemed like whatever was driving the motor wasn’t responding to input from the switches activated by notches on the cam, and was often not rotating the cam to the point where the switches would engage. Interesting, and infuriating. I’d tested the switches in various positions and they seemed to be working properly. I even cleaned the contacts with sandpaper to be sure. Did I mention there’s no manual for this on the internet? Yay! Today I replaced all the electrolytic caps on the board, despite the fact they tested OK, just to see what would happen. The turntable worked properly, I left it and tried again in the evening and it was still working properly so may have fixed it. Tomorrow will tell. The problem has the feel of something not charging/discharging properly, and the not working next day seems consistent with this – it’s like turning the unit on and off a few times charges reluctant caps, which then operate, but after being left overnight they’re flat as a pancake. Maybe this turntable has been sitting unused for years – and maybe I don’t understand how capacitors work!

This thing has turned out to be a massive pain – I replaced the 4013 series flip-flop IC as a last resort but it fixed nothing. I think there’s definitely something wrong with IC01, the BA6134. Pin 2 is meant to be 0V according to the service manual, but fluctuates between 7V and 0.5 – 3V. At the lower voltage, the mechanism works correctly, at the higher voltage it doesn’t. I had previously disabled the LDR/LED part of the circuit and it had allowed manual use of the turntable, but this time ’round it doesn’t – nothing works properly, even if I replace the LDRs with resistors equivalent to the value they operate the mechanism at. The arm won’t lift or lower, and if it does lower the quartz lock light goes out and the platter stops. Removing the LDR/LED unit from its mount and setting it aside allows the LED to shine onto both LDRs and nothing happens. Covering the outboard LDR makes the arm move to the start of the record but not lower, covering the inboard LDR makes the arm return. Covering both makes the arm lower and the platter stop. None of this adds up to a usable, manual turntable – everything is so closely integrated that every part has to work correctly or none of it does. So it looks like I’m done with this particular beast – unless a BA6134 emerges in the future.

 

Atten 858D+ Rework Station – Unsafe & Faulty: Fixed!

I got this the other day, $121 from China with free shipping, and it got here in a week!

After reading some cautionary postings on the EEV Blog, I decided to pull it apart and check it. First thing I noticed, they were switching the neutral line, not the active. I reversed the cables. The fuse was fortunately across the active line – the IEC socket had a built-in fuseholder so there was no option! Then I opened up the handset and noticed the earth wire wasn’t connected – it was a piece of braid spot-welded to the metal housing, and was just dangling in space. I tried soldering to the braid, but couldn’t despite using flux and turning the heat up on my iron. So I removed the braid, cut a small slot in the housing with my Dremel, bent an earth lug, fed it through the slot then crimped and soldered it in place. I realise the hot air station is designed to melt solder and using solder to secure the lug is probably not the smartest thing to do! However, I didn’t have a spot-welder and there wasn’t space to bolt the lug to the housing. The solder is just stabilising a mechanical connection, is at the opposite-to-business end of the handset, and with the fan blowing hot air away from it I thought there wouldn’t be a problem. I will of course re-check it thoroughly after the first proper use. I soldered a wire between the lug and the earth trace on the handset PCB. I measured continuity and resistance between the handset and the earth lug bolted to the transformer. The connection between the wire, lug and transformer wasn’t brilliant, so I improved it – new lug, shakeproof washers, longer bolt and two locknuts. I put a piece of heavier gauge wire between the transformer lug and earth terminal on the IEC socket, heatshrunk every connection, then PAT tested the unit. I also performed a leakage current test just to be on the safe side. It tested correctly, and I cautiously powered it up. There was a bit of smoke from the handset initially, which I took to be the flux I’d used burning off. I haven’t had a chance to try it out properly, but will write more when I do.

So after using it a few times – desoldering, melting hot glue that was holding a cable in place – I have to say it seems next to useless. I can turn it up to nearly its maximum, and the board I’m pointing it at gets hot enough, but solder doesn’t flow even if I use flux and have previously added lower melting-point solder to the joint with my Hakko iron. Mystifying. Maybe I’m just not doing it right. Hmmm.

So after ordering a new handpiece last night – NZ$14 with free shipping – I opened up the unit just to check the board and connections. The middle pin of the air speed potentiometer hadn’t been soldered at all! I remedied that, and added some solder to components that seemed to need it – it’s a double-sided board and joints on the top side seemed lacking. Buttoned it up and tried it out – in about 20 seconds I’d removed the big shield from an iPhone logic board, so I guess it’s working as it should, finally!

Atten 858D+ Rework Station: excellent value for money, but unsafe and faulty. Needs to be carefully inspected before use by someone who knows what they’re doing. Other than that, cheap hot air for the hobbyist!

Adventures in old tech…until your mind reels…