Panasonic DMR-EZ27 Repair.

Skinny sent me a message on Facebook....

"Mum's DVD recorder has gone wrong. Can you take a look?"

Yeah, why not...

It's a rather nice Panasonic unit. I like Panasonic stuff. This one has failed completely dead...

Off with the lid, and the fault is immediately obvious... (or so I thought)

C1401 has had enough and blown his top... he smooths the 5V rail. In this case it's 1,200uF at 6.3V. I didn't have one, so I fitted a 1,500uF, 16V part...

Watch out for the charge remaining on the main reservoir capacitor.

Plugging the unit back in..... and .... nothing :( It looks like the power supply isn't starting up. A quick check of the capacitor in the current stimulation supply in the primary shows it's in bad shape. It's a 68uF 35V part. It's ESR was over 30 Ohms. I fitted a 68uF 63V part and tried again.

Bingo!

Another saved from landfill!

The guilty parties ....

Building Frank C's Hedghog 625 PAL to 405 System A standards converter.

It's time to big up someone else's project.

Enter Frank C's Hedghog converter...

Details of the project an be found here.. http://electronics.frankcuffe.ovh/hedghog

It's a stunning project, and features a few useful functions not found on my other standards converter, the Aurora SCRF405 (which for those of you who don't fancy the DIY approach, can be found here http://www.tech-retro.com/Aurora_Design/Single_Converter.html)

It consists of a digital video converter (The TVP5150) which converts PAL to an 8-bit ITU−R BT.656 format. These one's and zero's are fed to an EP2C5 FPGA development board, which mounts to the top of the PCB. The magic happens in here, and the resultant 405 line system A video output emerges from the resistor ladder DAC. This is then passed to a MC44BS373 modulator IC, which is tunable on all Band I and Band III channels. The tuning of the modulator is also taken care of within the FPGA, and is set with a hex switch. There's a second MC44BS373 which is modulating audio at the required 3.5MHZ spacing below the vision carrier.

The unit produces aspect ratios of both 4:3 and 5:4 (5:4 being in use up to 1950)
There's a Pedestal function which lifts black level 50 mV above blanking level. This was abandoned on transmitters post-war, as it reduced the efficiency of the transmitters. It may help with early sets that suffer from flyback lines.
You can select between normal broad pulses or broad pulses with equalising pulses. Equalising pulses were never in the spec, although it may help interlace on some sets (ironically it upsets interlace on some, and causes the top of the picture on some Bush sets to "hook")
The three-line interpolator has three settings: soft, medium and sharp interpolation apertures.
Switchable 1KHz or 400Hz test tones.
There's also a PM5544'esque test pattern, and stair-steps.

These functions are all available via switches on the front panel.

PCBs were ordered from the most-excellent pcbway.com, and arrived within 7 days.

The FPGA board came from eBay.
The MC44BS373's I had to source from AliExpress, as it's now classed as obsolete, however, at the time of writing this, there appears to be plenty of stock from "grey" suppliers. I dislike doing this, as many times I have been caught out with fake parts! Caveat Emptor. I used the AliExpress supplier YT Electronics components co.,ltd


The phono sockets also came from AliExpress (link) and fit with a minor modification.

Assembly is straight forward, don't let the surface mount put you off. Get a decent quality gel flux. If you've seen my videos, you may have realised I suffer with a benign tremor (nothing to worry about, I've had it since I was 14), and I can mount this stuff with ease. I do have the advantage of a microscope.

A bit of blue-tac helps hold the board in place. First off I fit the semi's.

Then the passives...

Programming the FPGA is straight-forward in windows, using the Quartus II (13.0 sp1) software, and the "USB-blaster" supplied with the FPGA board. I failed to get the software to work under Ubuntu (although it would "see" the programmer hardware, the program option remained unavailable). When correctly programmed, there's a binary counter running on three LEDs on the board.

 Sockets and switches are mounted.

And the FPGA board fitted.

... and it's switched on!











However, some fault finding was required, as although the test patterns and test tones were OK, there was no converted video. With the help of the designer, Frank and the VRAT forum (here), it was apparent something was wrong with my FPGA board. After some fault-finding, a tiny solder bridge was found on the FPGA board, shorting out two of the lines. Once this was removed, the converter worked faultlessly.

Moire pattern is being caused by the camera, the actual picture quality is superb.

I like the additional functions available from the front panel. Picture quality appears to be on a par with the aurora converter.

What I'd really like is a centre-cut out function for dealing with a 16:9 input.... Frank?

CCT811 Video modulator massive failure.

Remember my warnings and concern about the CCT811 video modulator?

This is the offending model in question. Apparently it's also being sold under various guises, one model quoted to me is the RF9000. If it looks like this, I'd be seriously concerned....

I wrote about it here. Please take a moment to read this, if you haven't seen it before.

Well, settling down for an afternoon of vintage TV fun, I switched the video rack on....

Crack, crack, crack, bang! Uh-oh...

"It's bound to be the modulator" I thought.


I was right. It had opened the fuse I'd retro-fitted. (If you have one of these awful modulators, time to stop using it!) Damned glad I fitted one... lord knows what would have happened if it had tried to short out the mains without the protection of a fuse... Fire would have been a REAL possibility.

I opened it up and expected to find a mass of blackened bits, but no.  Now I've giving up on this I thought... but it's so useful!

It looks as though the insulation had failed on the transformer, and destroyed the semi-conductors in the drive-side of the supply.

I thought I'd remove the ghastly existing "switched-mode" blocking oscillator, and replace it with something ...

1) Electrically safe.
2) Reliable.

OK. First things first. To find out if it still functions.

I removed the transformer, and connected the workshop power supply between the end of the rectifier diode, and ground....






It seems to want about 6.5 VDC to operate, and has even remembered the settings it had before the power supply failed... good.

It's drawing about 165mA at that voltage, so a supply is not too challenging!

I decided to have a look in the drawer of redundant wall-warts to see if I could find anything suitable, and I spy one of my favourites, an old Nokia phone charger!

Now I always pick these up from boot-sales for a few pence, and are very useful. This one is rated at 3.7 Volts, at 350mA...

"But Andy, you said the modulator needs 6.5 volts to work" ... and so it does, but this particular Nokia charger is unregulated. Off-load it makes about 10 Volts.... Will it make our 6.5 volts at 165mA?

I solder the white +VE lead to the anode of D107, and the black lead to the far right hole (viewed from the rear of the modulator) left behind when I removed the transformer...










... and switch on....

Eureka! It works.










So it's now electrically safe, and I can sit back, and watch some "proper" TV....

Video rack video modulator repair and warning! Model CCT811

Remember the video rack I built a while ago? It's details are here.

Well, it's developed a fault. The UHF modulator has been giving very poor pictures after a few minutes of operation. I decided to take it out, and repair it.

IF YOU HAVE ONE OF THESE UNITS, I WOULD HAVE SERIOUS RESERVATIONS ABOUT IT'S ELECTRICAL SAFETY. 

I purchased it ages ago from eBay, and it came fitted with an unfused euro plug, which I cut off, and fitted a standard UK Plug, and fused it at 1 amp. I'm glad I did... read on ...

It's a useful thing. Is stable (when working properly), is adjustable throughout European VHF allocations, as well as UHF, and has switchable FM sound between 5.5 MHz and 6 MHz sound sub-carriers....

Disassembling the unit reveals a few horrors....

Check the mains input to the diminutive switched-mode supply ..... No fuse is evident!

What you can't see by this picture is the bottom of the case, the black bit. It's metal. There's no earth, which would be fine if the thing met Double Insulated (Class II) standards, which I doubt it does. You can read about classes here.

There's also zero filtering on the mains input, so any noise from the switched mode makes it's merry way back down the mains lead and out onto our mains, spoiling our radio reception (and, ironically, our TV reception too!) if it radiates (which it will).

Grim. Glad I fitted a fused plug ....

Examination of the power supply shows it to be nothing more than a simple blocking oscillator.

There's a simple zener on the output attempting to provide a little regulation. You can see where the board is a little discoloured, as it's been running warm. There are two capacitors in the primary, the mains smoothing capacitor (4.7uF 400V) proved to be very low in capacity. I fitted a 10uF , as I had one to hand. I also changed the smaller cap (10uF 50v) whilst I was there.

 A quick check shows the unit to be working again.... but what to do about the safety issues?

Mounting it back in the rack, I've fitted an in line filter and fuse (100mA). I'm not so concerned about earthing the case, as the modulator is inaccessible when the rack is assembled, that doesn't mean you should be though!

Pity really ... "for a ha'p'orth of tar" an otherwise good unit is spoiled.... and possibly electrically unsafe and a fire risk. It carries a CE mark, which I've no doubt it doesn't deserve.

 This gives you some idea of the size of that supply transformer, that's a 1p piece!

The guilty parties. Caps. As usual!

Workshop video rack.

Whilst I don't get as much time as I'd like to "play tellys", the state of the workshop video sources has been plaguing me recently.

For those outside the UK, I'll explain a little. All TV transmissions in the UK are now digital. They're delivered in Band IV UHF.

In times gone by, there used to be a 405 line black and white only service (System A). This existed  from 1936 until 1984 and started out in Band I VHF, and then expanded into Band III when ITV started in 1955. 625 lines (System I) was introduced for the start of the BBC2 service in 1964, in UHF only (it went colour (PAL) in 1967, and all services moved to UHF 625, both in bands IV and V (Band V has now been flogged off to the mobile phone operators for 4G etc.) )

Now, to run my old tellys we need to generate at least some of these signals. The UHF 625 line colour stuff is easy, just get a DVB receiver (Freeview) with a modulator built in. 405 lines is a little more tricky, but thankfully there exists a small box called an Aurora, which is a 625 line to 405 converter (there are other types available too, to convert between almost anything!)  with a built in VHF modulator. It's superb. Auroras (Auroae?) can be found here. If you are inside the EU, you can order them from Crowthorne tubes here.

The big problem is this motly collection  of boxes and power  supplies, the odd DVD player etc, has just been jury rigged as required. Not a satisfactory situation.

So, I designed myself a little rack to house it all.

 All connections are made on the front panel. This is a workshop piece of equipment, and you don't want to go fiddling around the back. The signal from our aerial (with our digital TV signal on) feeds the top Belling Lee socket, this is passed to a "4G" filter to remove any signals from band V. The RF then feeds the two freeview boxes and the outputs from these (in Band V) are mixed and sent to the mixer in a UHF modulator. The band I output from the Aurora standards converter feeds an attenuator (it's output is hot!) and a low pass filter, this is then combined with the UHF RF and passed (finally!) to the lower Belling Lee locket for connection to the set or sets.





Video to the standards converter is switchable from nothing (which causes the Aurora to output test card C), the Aux input sockets on the front, the DVD or either freeview receivers. Video to the UHF modulator can be switched from the Aux sockets or the DVD player (The freeview is already modulated)





 Much neater and I'm rather pleased with how it's all come out.

I've subsequently added a small Sumvision Cyclone media player to the set up, which is great for playing video files and test cards from a USB memory stick.