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Old 16th November 2014, 04:45 PM
moley moley is offline
Join Date: Nov 2014
Location: Sheffield
Posts: 30
Default Re: Help - Phono 3 Heater voltage Measurements

Hello folks,

Thank you very much for your replies and advice on what to investigate.

-As I have put heat shrink on the back of the binder power socket I can't take a voltage reading from the back of the socket but I have checked the continuity of the pins on the other side to the correct places and there are no shorts between the pins.

-I have low resistance between HTR+ and HTR- until the valves are removed then it becomes open circuit.

-I checked again the voltages coming from the PSU cable by measuring at the pins in the cable and these are correct with 405 volts top left, zero top right, 53 volts bottom left and 60 volts bottom right.

-Both earth connections of green wire show continuity back to the smoothing cap.

- If I measure the junction between r29 AND r31 at the HT+ point I get 403 volts withouth the valves in but with the valves in this becomes 270 volts in line with the manual.

- still measuring the HTR+ to PSU chassis ground (with DC mode on the multimeter) I get
3.49 volts and -3.13 volts on HTR- to PSU chassis ground. This is without the valves in. Reading across HTR+ and HTR- I get 6.62 volts.These readings are repeated across the other two sets of HTR+ and HTR-.

- I checked that there are no shorts between the pins of the PSU cable coming from the PSU and oddly there seems to be a tiny amount of continuity between the bottom two pins which connect to the brown and grey wires in the phono 3. The multimeter gives a tiny very short beep but doesn't give a reading like there is a small connection that comes and then goes. If I leave the test probes on the continuity is gone but if I lift them and then place them back I get a very short quiet beep again.

I removed the PSU cable from the PSU and tested this and the shorts were gone so I got inside the PSU and tested the grey and brown heater PCB points leading to the two PSU sockects and again I get the tiny amounts of continuity that appear, disapper and only reappear if I lift the test probes and place them down again. Is this at all normal? Is this due to continuity that exists within the PSU circuit but my multimeter DC signal is then blocked by some of the components in there?

- With regards to other checks inside the PSU. C5 is the correct way around with the stripe against the negative connection. My voltages look ok looking at the schematic which shows 53 and 60 volts output respectively. R5 is 100 ohms. R2 and R3 look correct per the coded bandings, although putting a multimeter on them to check, the reading keeps slowly increasing. In the case of R2 it climbs from 30k slowly up past 150K to around 169K where is slows right down and stops. Similarly R3 behaves this way too going from around 5k to 20.6K where it stops. Other resistors test as normal with a correct reading straight away.

Many thanks again in advance for any advice on this!
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