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Old 9th Jun 2019, 8:27 pm   #19
MickMcmichael
Pentode
 
Join Date: Mar 2009
Location: Peterborough, Cambridgeshire, UK.
Posts: 196
Default Re: Alba TC1525 G6 Dual Standard.

Some progress to report. Odd issues still abound!

Replacement IF gone in. Leads resoldered into position. Check once, check twice, check again and switch on ... hold it, wait a minute, something doesn't look right. Switch off.

Someone in the past had replaced a wirewound resistor in the power supply on the tagstrip at the bottom of the chassis. They had soldered two resistors in series to make up 220 ohms.

In the process of moving all the leads about to replace the IF, I had moved these two series resistors to one side and noticed that there was a gap, a space on the tagstrip that's not shown in the component layout.

The component layout says that there should be R1072 in this vacant space. It feeds 12v to the tuner and is 15k in value. It was gone - not there - disappeared!

Switch on again and watch the replacement IF for smoke. None to be seen. Venture into set with meter probe to the tuner. No 12v !

Fit hefty 15k to the vacant position (it basically turns 220v into 12v with a bit of heat dissipation!). Switch on again, apply RF signal from freeview box and wait.

Buzz buzz. Tune button 1 on tuner and get full sound but still blank raster; a bit pink. I thought I could see some movement in the raster so I turned up the brightness. The relay clicked on the tube base. The 12v supply which I'd just restored went down to 8v and sound disappeared. Turned brightness down again, relay clicked and sound came back. 12v restored. Uh?

How odd!

But it's definitely progress. There's apparently two 12v supplies to the tuner so I need to check both. But if someone had actually removed a 15k resistor from the power supply, what else is missing?

Time will tell. All good fun.
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