Otari MX5050 mk3/8 Capacitor problems - UK Vintage Radio Repair and Restoration Discussion Forum

vintage radio · 1st Sep 2018, 9:45 pm

Stupidly because of bad advice I changed 5 caps on the main board 2x4700uF 35V, 2x1000uF 63V and 1x 4700uF 16V, the recorder was hum free with perfect audio, just a few minor logic issues on counter and transport. Now it has massive hum.

I never discharged the caps before unsoldering. Has anybody an idea what parts in the circuit I might have damaged?

Thanks.

Ted Kendall · 2nd Sep 2018, 11:35 am

Are the new ones the right way round?

NorfolkDaveUK · 2nd Sep 2018, 11:58 am

Firstly , not discharging the caps wont cause any damage to the boards . So dont panic there . The only real harm in that is it making you jump if the spark at you usually find a good expletive useful in that situation , secondly . As Ted says , check the polarity is correct on the caps . It was good advice to change the caps if they are the original ones , they go bad after time and really all caps need changing at this age so you are doing the right thing . They do have a + and - so make sure the side with the stripe is going to negative . putting them in backwards wont blow anything except the cap (usually), but it wont work either . Also make sure you didnt accidentally knock off a grounding wire or anything , I`m always doing it ..hehe.

acorn · 11th Sep 2018, 4:07 pm

Try another cap across the five caps you have changed one by one and notice any difference in hum level or it could be the earth conection on the board to chassis has broken, try a meter from the negative tags on the caps to chassis earth and note the reading.

Acorn

1st Sep 2018, 9:45 pm	#1
vintage radio Diode Join Date: May 2011 Location: London, UK. Posts: 2	Otari MX5050 mk3/8 Capacitor problems Stupidly because of bad advice I changed 5 caps on the main board 2x4700uF 35V, 2x1000uF 63V and 1x 4700uF 16V, the recorder was hum free with perfect audio, just a few minor logic issues on counter and transport. Now it has massive hum. I never discharged the caps before unsoldering. Has anybody an idea what parts in the circuit I might have damaged? Thanks.

2nd Sep 2018, 11:35 am	#2
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Otari MX5050 mk3/8 Capacitor problems Are the new ones the right way round?

2nd Sep 2018, 11:58 am	#3
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Otari MX5050 mk3/8 Capacitor problems Firstly , not discharging the caps wont cause any damage to the boards . So dont panic there . The only real harm in that is it making you jump if the spark at you usually find a good expletive useful in that situation , secondly . As Ted says , check the polarity is correct on the caps . It was good advice to change the caps if they are the original ones , they go bad after time and really all caps need changing at this age so you are doing the right thing . They do have a + and - so make sure the side with the stripe is going to negative . putting them in backwards wont blow anything except the cap (usually), but it wont work either . Also make sure you didnt accidentally knock off a grounding wire or anything , I`m always doing it ..hehe.

11th Sep 2018, 4:07 pm	#4
acorn Pentode Join Date: Aug 2006 Location: Dorchester, Dorset, UK. Posts: 114	Re: Otari MX5050 mk3/8 Capacitor problems Try another cap across the five caps you have changed one by one and notice any difference in hum level or it could be the earth conection on the board to chassis has broken, try a meter from the negative tags on the caps to chassis earth and note the reading. Acorn