Ferguson 3629 "Personal" Dual-standard monochome television receiver restoration.

It's nearly my birthday, so I thought the wife may turn a blind eye to a "new" TV. There's a sort of "gap" in the collection with regards to 60's dual-standard (405 line/ 625 line) monochrome sets. Then this turned up....

 It's a Ferguson 3629 "Personal" Television, using the Thorn 900 Chassis.

It's a compact set. The 900 chassis is often referred to as the "cool" chassis, designed to use less energy. It features no wasteful "dropper" resistor to obtain the correct voltages, but a mains auto transformer.

 This particular set dates from 1965, and has the early valve UHF Tuner. Later models had a much improved transistor UHF tuner. The VHF Turret tuner can be seen on the right, the UHF tuner on the left. The UHF tuner has the valves enclosed in small screw-on caps.

 Diminutive Mazda CME 1101 CRT

Red EHT rectifier tray. This is semi-conductor, and is mounted on top of the very reliable "jelly-pot" line output transformer.

The system switch can be seen running the whole length of the chassis. This is moved by a switch on the front panel, which moves a flexible cable, which in turn operates the system switch, and a switch on the VHF tuner.

Initial results are encouraging. Very poor frame linearity, and hold. Usually caused by a poor PCL805 or it's cathode decoupling. Not in this case, however! As usual, it was down to a capacitor on the secondary of the frame output transformer. Bob the bodger had previously been at work around the frame stage, and had fitted two replacement resistors (of the wrong value!) and a cap (of the wrong value!) After these were replaced, results on 405 lines were encouraging.

Initial results... poor linearity and frame lock.










UHF 625 operation was not good. Signals are available from my test rack at UHF channel 40, 50 and 60. In addition to signals on 36 and 68 from the house distribution system.

Reception on Ch 36 was OK, if a little grainy. Channel 60 was available strongly, although was extremely touchy to tune, and Channel 68 was good. Where are 40 and 50?

 UHF tuner removed...

 Valves inspected...

 Fine tuning mech cleaned and lubricated. Be very careful not to move any wiring!

 Apparently the small disc ceramic capacitor can crack, it's just to the left of the red coil... it's OK in this tuner.

It turns out that the PC88 is the guilty party!

 Good pictures on 405....

... and 625. After a few minutes some hum starts to disturb the sound and picture.... It's pretty obvious a re-cap of the set will be required...

Quite a few caps are in physically poor condition, or electrically faulty and are replaced, along with the PC88....








The set then functions well, so I re-install the chassis into the cabinet. The set then suffers with intermittent frame collapse (no frame drive), leaving a horizontal line on the centre of the CRT....

After much probing about with an insulated screwdriver, I spot something arcing on the scan coils...

... it's a thermistor (or rather was!). It's turned into a blob of something... I don't have a replacement (and I've got precious little chance of getting one), so I shorted it out, restoring operation.







And here's a video of the set working...

1275GT - the rust continues (to be eliminated!)

Well, back in August the car came home (link here) , and it's been languishing back in the garage awaiting re-charging of funds.

I decided to bite the bullet and get a proper whole front panel. It wasn't cheap, but the front valance was shot. I was going to sped a few hours repairing it, but it had gone round the holes in the front badly, and that was going to be difficult to get right.

 Measurements are made, and spot welds drilled out.... there's some unpleasant bodgery around the headlamp surround. Thankfully the wings are sound.














... and the front comes off,

 The new one is fitted...











... took some cussing, and help from the wife....

... and is finally welded into place.











Now for paint ... (more funds required !!!)

Marantz PM6004 repair

A super chap called Richard from work collared me

"I've got a Marantz amp, intermittent low volume on the left hand channel, usually when changing between speakers A and B , and it only happens on one set of speakers..it's too good to throw out. Can you take a look?"

Yeah ... why not?

 Nice looking modern amp...

 ... and very nicely constructed.

 We're going to have to get the main board out, which is a bit of a struggle as usual, as all the sockets are connected straight to the main board. But before that, let's see if the amp will misbehave for us... Yep, one of the speaker protection relay's doesn't always make it across. They're only rated to 5 amps, which seems a little low for my liking, so some 10 amp relays are obtained, and fitted.

 Here are the guilty parties. Actually only one was faulty, but I changed both to be on the safe side. A check of the bias (it was fine) and a good soak test. An easy fix.








When I returned the amp, the guy said it had always done this since new, and had been returned under warranty twice. Each time it was returned stating "no fault found". I would have thought it was obvious, once the customer's speakers and wiring were eliminated from the equation...

Luxman L&G L2800 Amplifier.

This arrived ... "Can you have look mate, been in the attic for years, plugged it in and it hums loudly and gets hot"...

... Yeah, why not.

I initially thought it was some sort of cheapo Japanese "nomark" amp...









Closer inspection reveals it to be made by L&G ... nope, me neither! A google search reveals it's made by Luxman, a well thought of brand in hifi circles, and this is from their L&G "more affordable" range. Apparently designed by Kimura-San of 47Labs & Gain-card fame.

It's of bog-standard 70's Japanese construction. Thankfully you can get to the print side of the board through a hole in the bottom.

A close look at the board shows there's either been some leakage of electrolyte form the caps, or there's been some sort of spillage. It certainly smells like a cat's litter-tray..

More signs of spillage.

This is a bit weird... there are two caps, mounted upside down, despite having more than enough space on the board... Here's one, there's the same on the other side of the board....

Nothing unusual about the output pair, NEC 2SD388A & 2SB541A on the left hand channel ...

nothing unusual that is, unit you look at the right hand channel....

... which is fitted with Toshiba 2SD371 & 2SB531 ! Apparently it's never been repaired before , so it must have left the factory like this! Perhaps they switched supplier and ran out halfway through making this amp!















A few cursory checks, and on with the mains, don't hold out much hope for the caps, but let's find out how bad things are. Left hand channel has a horrible 8V DC offset, and it's all humming very unpleasantly.

I think we'd better look at those caps. One by one, they are removed, tested and replaced. Some are open, some electrically leaking, many are physically leaking, and none are to tolerance, except the main split-rail smoothing caps, and those two caps mounted upside down!

After a comprehensive re-cap, things are improved, the DC off-set on the left channel is still way too high at 2V. I measure the bias of the right-hand channel at the 0.33 ohm emitter resistors. It's set for 80mA. I set the left the same, and then set the balance up for both channels. DC offset is less than 5mV for both channels.

Now the switch-gear and pots are all noisy, but really nicely made. A good clean up with some switch-cleaner and repeated operation sorts any switching issues and noisy pots are no more.

I soak test the amp for a couple of hours with some fine Yes music, re-checking the bias and offset after an hour, and it's all well. Sounds great, the phono stage is quiet, and it makes a good 50 watts into 8 ohms. Despite different transistors in each channel, I'm damned if I can tell!

The guilty parties ....

Arduino EEPROM eraser.

I'm working on a small commercial project at the moment, which requires me to store some data into the Arduino's EEPROM. When you upload a new sketch to the Arduino, the EEPROM remains unchanged.

Now a "virgin" arduino has every address in the EEPROM set to 0xFF. Here's a quick sketch to reset the EEPROM to as new, so you can test your code on a fresh arduino.

It outputs to the serial monitor, and blinks Pin 13 on completion.

Apologies for lack of comments, but it's straightforward enough...

 #include <EEPROM.h> //EEPROM interface
 int addr = 0;
 float len;
 int pcComplete;

void setup() {

 Serial.begin (9600);
 Serial.println ("EEPROM Eraser");
 Serial.print("Size of EEPROM =");
 len = EEPROM.length();
 Serial.print (len);
 Serial.println (" bytes");
 delay (1000);
 pinMode(13, OUTPUT);
 }



void loop() {
 EEPROM.write (addr,255);
 Serial.print (addr);
 Serial.print ("  ");
 pcComplete = (addr / len)*100;
 Serial.print (pcComplete);
 Serial.println ("%");
 addr ++;
 if (addr == len+1){
  addr = 0;
  Serial.println ("Complete");
  blinkPin();
  
 }
 }

 void blinkPin () {
  while (1) {
  digitalWrite(13, HIGH);  
  delay(1000);             
  digitalWrite(13, LOW);   
  delay(1000);             
  }
 }

Panasonic SC-HTB10 repairs.

Ugh ... soundbars. No. Not for me. A decent amp and speakers, why not? But the thought of an amp and speakers placed in a tiny enclosure to put under your telly, to improve the (usually) woefully inadequate speakers in a flat screen ... anyway ... rant over.

This is the Panasonic SC-HTB10 sound bar. It belongs to a colleague.

"It just clicks. Can you have a look?"

Yeah , why not...

Dis-assembly involves removal of the myriad of screws from the back, there are 4 hidden under rubber bungs on the corners. The back fits really tightly, I needed to gently pry it free using a "spudger" (one of those cheap plastic tools you get for taking mobile phones apart).

 This is the only time I've ever had to take a photo of a piece of kit in panorama mode!

You'll need to disconnect the sub-woofer which is in the back...

Neat tuning port!

Unplug the other two speaker plugs (blue and white, just by the green circuit board)








You should now be able to lift the electronics clear from the case.

Now, I'll just draw your attention to the disclaimer up there on the right of the webpage. Yep, that one. I'm doing that, because this one caught me out a bit. Under the pressed steel shield is the power supply (actually two supplies). Because of the symptoms, my guess was it was failing to start up. I carefully removed the shield and removed the supply.

Now, we can see there are two switched mode supplies. There's a small switched mode transformer above the date code, and a larger one below.

The small power supply supplies the micro-processor and control electronics. It's always on, so the remote is kept powered. This appeared to be functioning correctly.

The larger power supply, and the components in the area marked "HOT" are used to supply the amplifiers, This is where the fault lay. Despite the fact that this supply had been disconnected for many minutes, the large electrolytic still held an impressive ~300V DC. Whilst I avoided getting a shock, I was surprised to find this charge still remained. Having safely discharged the cap with a watty 10K resistor, I started a few checks. See how dis-coloured the board is around the switched mode controller and chopper IC 5701? Thing's have been running HOT! (The HOT marking on the board is to warn you that this part of the power supply is connected to live mains, and is not isolated! Not the temperature of the electronics!) Poor old C5726 had suffered as a result. It's ESR had risen to about 25 ohms... far too much for this capacitor to be in any health. A replacement was fitted and restored operation!

Another piece of gear saved from landfill 

Selmer "Futurama" Corvette repairs.

Float back to the 60's (man..) and Selmer was producing some really good "Truvoice" amps. Quite expensive though... then in the early 60's (around 1963, to match their Futurama guitars) they released some budget amps.

This has wandered in to the workshop...

It's a series two amp, dating from 1965. Schematic can be found here. It's a simple enough circuit, two ECC83's and EZ80 rectifier and an EL84 output valve. 

Cosmetically, it's in really good nick...

There's a little storage compartment in the back for the mains lead and tremolo foot switch.






This one's not so good electrically. Switching it on, it just hums loudly.

The amp is constructed on a small PCB, mounted on the rear of the front panel. The output transformer is on the left of the chassis, and the mains transformer on the bottom of the cabinet. It has a three core mains lead, and is nicely earthed, unlike the WEM copycat!






Removal of the chassis for service requires removal of the four screws attaching the front panel.









Investigation into the hum shows the main HT smoother cap to be totally unservicable. Once again the dreadnaught lets me down, you can't win 'em all....!

To preserve the look of this lovely amp, we'll re-stuff the original 32+32uF cap with modern equivalents...



First of all cut around the bottom of the can. I use a sharp craft knife, scoring round until the blade is able to pierce the aluminium can. Wear some rubber gloves.

Next, warm the can up with a hot air gun in a well ventilated area, and get a large screw, and screw it into the capacitor. (This is a concrete screw, they're really good for putting up shelves! No wall plug required!)














Grab the screw with a pair of pliers and gently pull to extract the insides...











Now make up two modern 33uF (450V in this case) capacitors, and solder them to the base. The can is the negative for both caps in this instance (it usually is, but best to check!)

If you can't get the leads through the original rivets, drill them out (or drill holes though them) so you can pass the leads through.

A lap of PVC tape to prevent any nasty shorts catching us out....


















And get the whole thing together in a vice so we can re-attach the can to the base...

Here I've used a little Alusol (aluminium solder) to tack the can to the base, so there's an electrical connection there. It's a bit of a pig to do, and you'll definitely need some fume extraction, that Alusol gives off some really nasty fumes.



Finish off with some hot melt glue...  and tidy up with a craft knife.










Once this was replaced, I was rewarded with a hum-free amplifier... but that wasn't quite the end of the story. The tremelo didn't work (Why, oh why, am I always plagued with tremolo circuits?!?!)

A few checks round showed a 100K anode load resistor to one half of the ECC83 (V2, the tremelo low frequency oscillator) was very high in value, having risen to ~4 Megohm. Replacing this restored tremelo operation ... but I couldn't switch it off ! The wire to the foot switch proved to have a break in it somewhere.... replacement sorted that. A quick squirt of de-oxit sorted any noisy pots out, and that completed the repair.