Hi fellas,
I can't follow along due to a lack of service information. Those regulators that are mounted on the main heat sink have occasionally failed, but that is not a trait these sets share. I think the added heat from the output stage causes an early death. BTW, the bias current setting for the output stage has to be that high. The design of the Stassis circuit demands it. However, don't run it over that value either.
The failing transistors switch B+, so I would expect the emitters to come off a positive supply.
-Chris
I can't follow along due to a lack of service information. Those regulators that are mounted on the main heat sink have occasionally failed, but that is not a trait these sets share. I think the added heat from the output stage causes an early death. BTW, the bias current setting for the output stage has to be that high. The design of the Stassis circuit demands it. However, don't run it over that value either.
The failing transistors switch B+, so I would expect the emitters to come off a positive supply.
-Chris
Hi JHanko,
The parts you are interested in are mounted on the tuner PCB. I think they were either TO-92 (TO-92M) or possibly TO-126 case styles. I'm pretty sure you are on the right track there. I think they tend to fail open after a period of being intermittent. Now, there's a change!
-Chris
The parts you are interested in are mounted on the tuner PCB. I think they were either TO-92 (TO-92M) or possibly TO-126 case styles. I'm pretty sure you are on the right track there. I think they tend to fail open after a period of being intermittent. Now, there's a change!
-Chris
Chirs I got the print from HI FI ENGINE .
Just making sure that the voltages are where they are suposed to be.
And I will try to trace if there is an AFC circuit possibly pulling it off of frequency.
As well as a closer look at the charge pump circuit If a scope is available.
I would hate to rule in a bad PLL but don't think that this is the case since it apears fine in AM mode, but you never know as I have seen stranger things happen. jer
Just making sure that the voltages are where they are suposed to be.
And I will try to trace if there is an AFC circuit possibly pulling it off of frequency.
As well as a closer look at the charge pump circuit If a scope is available.
I would hate to rule in a bad PLL but don't think that this is the case since it apears fine in AM mode, but you never know as I have seen stranger things happen. jer
Meanwhile check the voltages on the PLL pins according print and note if any of them to be significantly off compared to the print especialy any that are low or missing.
And be very careful when doing this usualy nothing will happen should you slip do to the very low voltages, but you never know. jer
And be very careful when doing this usualy nothing will happen should you slip do to the very low voltages, but you never know. jer
An oscilloscope would be the perfect device to examine the tuning voltage with. I do that as a basic test.
Another idea that is less expensive though. Why not capacitively couple that VT line to an amplifier input? Then you could hear if there was anything there. It should be pretty silent. Use a plastic coupling capacitor of 1 uF or better. Make sure you don't change the tuning while the volume is turned up!
All you need for this is a good capacitor, and the AUX input on an amplifier / receiver with a resistor (10K ~ 56K approx.) across the input to discharge or charge the capacitor. I guess a cut RCA cable might help as well.
Hi JHanko,
Oscilloscopes are fairly inexpensive these days. Used ones are cheap, and a USB type would give you very advanced features for cheap as well. The only thing you need to watch is that the USB products normally have a maximum peak input voltage of 5 volts. So that means if you use a 10X probe, you have a 50 volt hard ceiling. Since you were use to using an oscilloscope, this would be the one change that would trip you up.
-Chris
-Chris
Another idea that is less expensive though. Why not capacitively couple that VT line to an amplifier input? Then you could hear if there was anything there. It should be pretty silent. Use a plastic coupling capacitor of 1 uF or better. Make sure you don't change the tuning while the volume is turned up!
All you need for this is a good capacitor, and the AUX input on an amplifier / receiver with a resistor (10K ~ 56K approx.) across the input to discharge or charge the capacitor. I guess a cut RCA cable might help as well.
Hi JHanko,
Oscilloscopes are fairly inexpensive these days. Used ones are cheap, and a USB type would give you very advanced features for cheap as well. The only thing you need to watch is that the USB products normally have a maximum peak input voltage of 5 volts. So that means if you use a 10X probe, you have a 50 volt hard ceiling. Since you were use to using an oscilloscope, this would be the one change that would trip you up.
-Chris
-Chris
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