Re: 2465A +5vd Power Supply Problem


 

All


4.7Kohm resistor in parallel with  R1270 no difference in +5d output Still low at 4.55v either way


27kohm resistor in parallel with R1044 no difference either in +5d voltage


Voltage at Pin 7 of T1060 and Ref 2 is 113 volts



Resistance from chassis ground to junction of L1110 and C1110 is 145 ohms (no load on +5d). Reversing the multimeter and it starts at over 140 Mohm and slowly draws down.


Link below is a photo of the ripple output at the junction of L1110 and C1110 with a load on +5d. Looks like the inverter puts out a a fair bit of noise


http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/888008784/lightbox/222918246

 








 



--- In TekScopes@..., <tekscopes@...> wrote:

David,
Shouldn't it be possible to test this by bridging R1044 with a 27 K resistor?  If the +5 Vd supply voltage increases we know its the optocoupler.

From: David <davidwhess@...>
To: TekScopes@...
Sent: Tuesday, September 10, 2013 4:28 AM
Subject: Re: [TekScopes] RE: RE: 2465A +5vd Power Supply Problem
 
1.07 volts indicates that either the optocoupler is bad do to low or no output, R1044 is open, or that there is an open circuit in series with R1044 and the optocoupler output. I was wrong earlier about the possibility of C1048 being shorted.

All of my service manuals so SOC123A which I suspect is a Tektronix house number. My Tektronix parts catalog shows Motorola MOC1005 which is a very close match to the Toshiba TLP631.

Current transfer ratio is the ratio of output to input current which is sort of like gain. 50% means that for every 1mA of input, the output will be 0.5mA. The optocouplers are graded by CTR which is why there is an F and GBF version.

The CTR should not be critical in this circuit so either of the ones you mention should work fine.

If you want another test to confirm where the problem is, then the voltage between pin 7 of T1060 and REF1 with an inverter load should be about 120 volts DC which indicates that the optocoupler output is missing and the pre-regulator is set for the minimum output voltage as determined by R1045 and R1046.

Another thing you could try is halving the value of R1270 on the low voltage regulator board near U1371C by temporarily placing a 3.9 or 4.7 kOhm resistor in parallel with it. That will double the current into the optocoupler so if its CTR has degraded with age, the higher current will allow it to work for now.

On 10 Sep 2013 00:10:39 -0700, you wrote:

>David:
>
>The voltage at Pin 1 to chassis ground was 1.07v (+5d is 4.5v)
>
>The service manual references U1040 as a TLP631 this is a Toshiba product and is still available from DigiKey There is two variants of this chip the
>
>TLP631-FND and the TLP631-GBF-ND. The F-ND has a current transfer ratio of 50%@5ma and the GBF-ND has a current transfer ratio of 100%@5ma. Whatever that all means?
>
>Machine Guy:
>
>I could not get any accurate measurements with all 3 comb connectors removed I had to leave P232 connected For what it is worth here is the measurements
>
>233B
>
>1 2v
>
>2 32v
>
>3 70v
>
>4 14v ?? this should be GND
>
>5 122v
>
>234B
>
>1 -8v
>
>2 0
>
>3 16v
>
>4 0v
>
>5 37v
>
>--- In TekScopes@..., <tekscopes@...> wrote:
>
>With the low voltage regulator board and your dummy load still attached measure:
>
>1. The voltage from pin 1 of U1040 to chassis ground or pin 2. The schematic says it should be about 0.96 volts but I bet it is higher because pin 8 of U1371C is very high which is to be expected when +5VD is low.
>
>If the voltage is low, below 0.96 volts, then the connection between pin 2 of U1040 and pin 8 of U1371C is open.
>If the voltage is high, above 0.96 volts, then R1044 could be open, or C1048 could be shorted, or most likely U1040 is dead.
>
>U1040 is an M0C1005 type optocoupler which I believe is a UL/VDE version of a 4N25 or 2N26. A CNY75A is the closest modern match I found but any of these 3 should work fine.
>
>I do not think the problem is with U1030 or anything to the left of the junction of R1045 and R1046 because with no feedback, the pre-regulator appears to be working correctly.
>
>I think machine guy was right when he said, "They use an optical feedback system to tweak the inverter and adjust +5 Vd. LED's age and are sensitive to noise. So that could be a source of inverter sag."
>
>On 09 Sep 2013 16:36:06 -0700, you wrote:
>
>>Hmm, I wonder if Pin 8 is so high because of a short in R1284 or R1285 or something with U1300B

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