Pioneer SX-410 help needed - UK Vintage Radio Repair and Restoration Discussion Forum

Paul Mathew · 16th Apr 2019, 11:13 am

Hi, I am trying to sort out this receiver/amp. Injecting a tone into the volume control works great, but I can't get any reception from either AM or FM stations. I've tried injecting a tone into the area around the 2 diodes which I assume is the detector portion of the radio circuit?, but nothing further back than the volume control pot VR2.
Any suggestions would be great.
I will upload the schematic, once I work out how to resize it!

Paul Mathew · 16th Apr 2019, 1:42 pm

Schematic attached.

ms660 · 16th Apr 2019, 2:25 pm

The two diodes you refer to are part of the ratio detector which is the detector for FM, injecting an audio signal at ratio detectors output at the junction of R84/C63 should result in an output from the loudspeaker when FM is selected.

So far as I can make out the AM detector is the last FM IF valve, injecting an audio signal at the AM detectors output at the junction of R74/R76 should also produce an output when AM is selected.

If no luck with those two test check the selector and tape monitor switch contacts, if those two tests check out ok it might be worth checking the voltages on V9 the FM/AM common IF amplifier and take it from there.

It goes without saying that the valve heaters should be lit.

Lawrence.

Paul Mathew · 16th Apr 2019, 2:39 pm

Thanks Lawrence. I did inject a signal at the junction you suggest on AM and FM, which led me to think the selector switch has lost a contact somewhere. I loosened it from the chassis, but still can't get good access due the rats nest of wires. Sprayed it with switch cleaner and gave it a working over. I'll do the other tests you suggest. The heaters are all lit and voltages check out within a reasonable tolerance compared to the schematic. When the selector switch is rotated, there is crackling on the speakers, so there is hope!

ms660 · 16th Apr 2019, 5:03 pm

It might be also worth noting that the HT supply to the FM front end, the last FM IF and the AM mixer/osc share a common route via R85 and R87 and S1 1/4R's contacts 1,3&4, 4 being the common, 4-1 for AM and 4-3 for FM.

Lawrence.

16th Apr 2019, 11:13 am	#1
Paul Mathew Pentode Join Date: Jan 2014 Location: Cape Town, South Africa Posts: 214	Pioneer SX-410 help needed Hi, I am trying to sort out this receiver/amp. Injecting a tone into the volume control works great, but I can't get any reception from either AM or FM stations. I've tried injecting a tone into the area around the 2 diodes which I assume is the detector portion of the radio circuit?, but nothing further back than the volume control pot VR2. Any suggestions would be great. I will upload the schematic, once I work out how to resize it! Attached Thumbnails

16th Apr 2019, 2:25 pm	#3
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Pioneer SX-410 help needed The two diodes you refer to are part of the ratio detector which is the detector for FM, injecting an audio signal at ratio detectors output at the junction of R84/C63 should result in an output from the loudspeaker when FM is selected. So far as I can make out the AM detector is the last FM IF valve, injecting an audio signal at the AM detectors output at the junction of R74/R76 should also produce an output when AM is selected. If no luck with those two test check the selector and tape monitor switch contacts, if those two tests check out ok it might be worth checking the voltages on V9 the FM/AM common IF amplifier and take it from there. It goes without saying that the valve heaters should be lit. Lawrence. Last edited by ms660; 16th Apr 2019 at 2:30 pm.

16th Apr 2019, 2:39 pm	#4
Paul Mathew Pentode Join Date: Jan 2014 Location: Cape Town, South Africa Posts: 214	Re: Pioneer SX-410 help needed Thanks Lawrence. I did inject a signal at the junction you suggest on AM and FM, which led me to think the selector switch has lost a contact somewhere. I loosened it from the chassis, but still can't get good access due the rats nest of wires. Sprayed it with switch cleaner and gave it a working over. I'll do the other tests you suggest. The heaters are all lit and voltages check out within a reasonable tolerance compared to the schematic. When the selector switch is rotated, there is crackling on the speakers, so there is hope!

16th Apr 2019, 5:03 pm	#5
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Pioneer SX-410 help needed It might be also worth noting that the HT supply to the FM front end, the last FM IF and the AM mixer/osc share a common route via R85 and R87 and S1 1/4R's contacts 1,3&4, 4 being the common, 4-1 for AM and 4-3 for FM. Lawrence.