Satellite Workshop 02
A lot of my repairs arrive by post. Most of them arrive reasonably well packed but today the postman placed the parcel carefully on the floor then ran. As I picked up the box I found out why - it rattled. To be fair, it wasn't the postman's fault. This Ferguson SRV1 receiver had been squeezed into a box which provided an exact fit. There was no resilient packing and the cardboard was single layer, not corrugated. It hadn't stood a chance.
When I pulled out the receiver, the front panel was detached and the cover had a large dent. I thought it was a no-hoper but, on removing the screws, I found just a tiny crack in the circuit board which had not propogated right through.
There was no letter with the unit but a 'Postit' sticker said: "Faulty. Please fix and add a crystal for more channels." I think the owner was a CB Radio fanatic.
I removed the circuit board and inspected it for damage. Apart from the tiny crack and the usual signs of overheating, there was none. I replaced C9 - always a wise precaution - then plugged it in to the mains. It zipped into life but gave a blank screen with no decoder board fitted. I switched to channel two and it produced a mass of horizontal lines with a hint of picture behind. The audio was fine and immediately I thought "tuner capacitor."
However, the picture was perfectly clear from the Decoder Scart socket! This is obviously not possible if the tuner is faulty so I began to poke around with the oscilloscope probe. Eventually I traced the problem to a dry joint on a surface mount capacitor below the TEA2029 sync separator. The picture was still a little streaky so I replaced all the electrolytics which usually dry out around the tuner and the power supply.
Having got a decent picture, I replaced the decoder board and retested the unit. The decoder worked all right but the "Please Wait" message was very faint. Reference to the "Satellite Secrets" book (I have a terrible memory) reminded me to check R92 on the decoder board. This had already been upgraded from 22k to 43k and the surface mount resistor, R342 beneath C171 on the main board had been replaced with a 680 Ohm.
Having eliminated the most obvious cause, therefore, I checked the power supply voltages. Here was a clue; they were all slightly low. Someone had correctly removed the surface mount capacitor which causes the 100 Ohm resistor to become hot. However, they had not replaced a zero Ohm link next to a 43k resistor with a 270 Ohm surface mount resistor. Once I'd done this, the voltages were correct and the decoder messages became much darker.
I was not sure if the customer was serious about increasing the number of channels but I fitted the ninety channel upgrade kit from Davenham Satellites. This consists of a new microprocessor and a tiny board with an EEPROM. When I applied mains power the Timer LED remained on for some twenty seconds while the micro reprogrammed the memory chip. Now the receiver was effectively an SS9200.
The only problem which remained was to repair the damage to the front panel. I decided that it was easier to fit the panel from a scrap SS9200 IRD. That fitted the bill nicely. A quick polish with a squirt of WD-40 and the unit was ready for packing. This time it would be done properly and the customer charged accordingly!