Roberts R900 easy repair - UK Vintage Radio Repair and Restoration Discussion Forum

Phil G4SPZ · 19th Aug 2023, 11:12 pm

This set arrived at my local Repair Cafe producing loud crackling from the volume control, but once treated with Servisol it transpired that the audio stages were working but there were no signals on any band. Looking at the circuit, the FM front end is a TA7358P and the AM radio is based on a TDA1220B. I deduced that the regulated 7.6 volt supply wasn’t reaching either chip, and quickly discovered that the decoupling capacitor C35 (470uF, 10V) had gone short-circuit. A replacement capacitor restored the set to normal operation.

Phil

Kevin Hoyland · 20th Aug 2023, 10:05 am

Morning Phil.
Good Work one more working radio.

Regards
Kevin.

Phil G4SPZ · 20th Aug 2023, 10:23 am

Morning Kevin, and many thanks - yes, I’ve lost count of how many radios and other electronic devices I have managed to save from landfill by the replacement of one single component costing a few pence. Probably the ‘best’ was a £350 electric feature fireplace which was dead due to a single 1Meg 1/8 watt resistor in the PSU having gone o/c!

19th Aug 2023, 11:12 pm	#1
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,675	Roberts R900 easy repair This set arrived at my local Repair Cafe producing loud crackling from the volume control, but once treated with Servisol it transpired that the audio stages were working but there were no signals on any band. Looking at the circuit, the FM front end is a TA7358P and the AM radio is based on a TDA1220B. I deduced that the regulated 7.6 volt supply wasn’t reaching either chip, and quickly discovered that the decoupling capacitor C35 (470uF, 10V) had gone short-circuit. A replacement capacitor restored the set to normal operation. Phil Attached Thumbnails __________________ Phil “The place where optimism most flourishes is the lunatic asylum” - Henry Havelock Ellis

20th Aug 2023, 10:05 am	#2
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 551	Re: Roberts R900 easy repair Morning Phil. Good Work one more working radio. Regards Kevin.

20th Aug 2023, 10:23 am	#3
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,675	Re: Roberts R900 easy repair Morning Kevin, and many thanks - yes, I’ve lost count of how many radios and other electronic devices I have managed to save from landfill by the replacement of one single component costing a few pence. Probably the ‘best’ was a £350 electric feature fireplace which was dead due to a single 1Meg 1/8 watt resistor in the PSU having gone o/c! __________________ Phil “The place where optimism most flourishes is the lunatic asylum” - Henry Havelock Ellis