Pioneer SX590, AM section only - UK Vintage Radio Repair and Restoration Discussion Forum

Ambientnoise · 30th Nov 2017, 12:31 pm

I am struggling with this one. Symptoms are very deaf and very distorted output, I can only hear anything with the pantry transmitter adjacent. The circuit uses an HA1197, effectively as per the data sheet. DC conditions are all correct, passive components all measure ok so resorted to replacing the chip but still the same. Using a scope, it seems OK up to the second IF which uses a Toko series LC in a can. The L seems OK but the C measures 280pf versus 180pf on the data sheet. This is on a cheapo Chinese tester so not sure of reliabilty of the test. Getting to this C is difficult!

Any thoughts, experience of the HA1197 ?

Thanks, Ken

tri-comp · 1st Dec 2017, 8:19 am

I've just fixed a Pioneer SX339 which is of course much later than the 590.
It was the FM-section acting up much like what you describe.
In the quadrature detector coil can the miniscule built-in capacitor was found to have drifted off initial value whatever that was.
The schematics only shows a cap., no value.
Resonance frequency checked with a grid-dip meter after unsoldering the coil can.
Can must be left in place over the coil to measure which will present a very low dip on the meter but enough to see the off-value.
In this case around 10,9MHz
Replacing it with an external 120pF cap. soldered across the correct coil pins below the PCB and very slightly adjusting the coil slug (~1/4 turn in) made the FM section come up to speed.
It could very well be the same kind of problem you're experiencing in the AM-IF imho.

Ambientnoise · 1st Dec 2017, 12:25 pm

Funny you should say that ! I bit the bullet and took out the second IFT. The integral cap measured ok but on a hunch I put 12v across it and it broke down to an IR of 1M. Back together with an external cap of 180pF and it is working well now. I did find web mentions of integral toko caps going bad.

Many tks for the response.

Ken

30th Nov 2017, 12:31 pm	#1
Ambientnoise Heptode Join Date: Feb 2006 Location: Marlborough, Wiltshire, UK. Posts: 915	Pioneer SX590, AM section only I am struggling with this one. Symptoms are very deaf and very distorted output, I can only hear anything with the pantry transmitter adjacent. The circuit uses an HA1197, effectively as per the data sheet. DC conditions are all correct, passive components all measure ok so resorted to replacing the chip but still the same. Using a scope, it seems OK up to the second IF which uses a Toko series LC in a can. The L seems OK but the C measures 280pf versus 180pf on the data sheet. This is on a cheapo Chinese tester so not sure of reliabilty of the test. Getting to this C is difficult! Any thoughts, experience of the HA1197 ? Thanks, Ken

1st Dec 2017, 8:19 am	#2
tri-comp Heptode Join Date: Oct 2008 Location: Aalborg, Denmark Posts: 903	Re: Pioneer SX590, AM section only I've just fixed a Pioneer SX339 which is of course much later than the 590. It was the FM-section acting up much like what you describe. In the quadrature detector coil can the miniscule built-in capacitor was found to have drifted off initial value whatever that was. The schematics only shows a cap., no value. Resonance frequency checked with a grid-dip meter after unsoldering the coil can. Can must be left in place over the coil to measure which will present a very low dip on the meter but enough to see the off-value. In this case around 10,9MHz Replacing it with an external 120pF cap. soldered across the correct coil pins below the PCB and very slightly adjusting the coil slug (~1/4 turn in) made the FM section come up to speed. It could very well be the same kind of problem you're experiencing in the AM-IF imho. Last edited by tri-comp; 1st Dec 2017 at 8:25 am.

1st Dec 2017, 12:25 pm	#3
Ambientnoise Heptode Join Date: Feb 2006 Location: Marlborough, Wiltshire, UK. Posts: 915	Re: Pioneer SX590, AM section only Funny you should say that ! I bit the bullet and took out the second IFT. The integral cap measured ok but on a hunch I put 12v across it and it broke down to an IR of 1M. Back together with an external cap of 180pF and it is working well now. I did find web mentions of integral toko caps going bad. Many tks for the response. Ken