Restoration of a really old hp5065a

[syau]

Continuous capacitor replacement today





Found that there is evidence of leakage at the bottom of the big C2 capacitor  Trying to find a 2800uF 40V replacement which is slim enough to hide in the bottom panel 

[5065AGuru]

Stanley,

I've only had to replace those big chassis mounted caps once.

I found a replacement that had screw terminals and used a piece of circuit board to make a mount that fit under the original hole.

Worked great.

Don't forget to check the 100uf cap in the A3 and A7 assemblies.

Cheers,

Corby

[james_s]

Another thing you can do when replacing big caps like that if you want to preserve the original appearance is to gut the original capacitor and slip a replacement up inside it. That can be tedious to do without damaging the housing but it is possible. It's easier if you can chuck it up in a lathe and neatly cut the bottom plate and then use an endmill to hog out the foil and paper.

[syau]

Corby,

Opened up the A7 and replaced the 100uF capacitor. During the process, found one capacitor C12 0.0252uF (the one with a thick plastic sleeve) has some “white powder” on it. Cleaned with IPA and looks good.

Not sure if it is electrically ok 



After 100uF replacement



Before cleaning



After cleaning



BRGds/Stanley

[syau]

Corby,

For the A3, I shine a light through the opening and the positive terminal of the capacitor looks good so I didn’t bother to open it up.

Just measured the main C2 capacitor, only a few hundred pF (not uF), C3 is still around 32xx uF.

For the 1.3k resistor in the lamp assembly, is 2W 1% resistor sufficient ?

BRGds/Stanley

[syau]

Wired a bridge rectifier and an external 3300uf capacitor to the unit, powered up with external 28VDC power supply, no magic smoke  (RVFR still not connected)



Hooked up to the AC, checked the output of 5MHz, 1Mhz, 100kHz on the check meter, all spot on. The only issue I have is I got a full scale deflection on the meter if I select OSC Oven. I measured the resistance between M & +24V gives 101 ohm which should be normal. Haven’t measured the AC heater 

I now connected the 5MHz output to my 53310A to measure the drift.

[syau]

Closer inspection found the previous owner has disconnected the 110V AC to the heater  The resistance if that heater found to be open circuit.

[5065AGuru]

Stanly,

The Oscillator will work fine without the AC fast warmup heater. It will just take longer to warmup!

Once its warm and you can verify it can be adjusted to exactly 5Mhz the osc oven indication might have come down.

If not you can reselect the resistor on A17 to pit it on scale.

2W 1% is OK.

One other thing, Before you power the receiver up check the the two chassis mounted transistors that go to A11. Make sure they are not shorted.

Also once you let the cell and lamp ovens warm up and the meter readings drop down you should test the transistors leakage. I just clip a resistor (500 Ohms or so) across the thermistor pins on A11 and make sure that each oven will completely shut off (meter drops to zero).

[syau]

Stanly,

The Oscillator will work fine without the AC fast warmup heater. It will just take longer to warmup!

Once its warm and you can verify it can be adjusted to exactly 5Mhz the osc oven indication might have come down.

If not you can reselect the resistor on A17 to pit it on scale.

2W 1% is OK.

One other thing, Before you power the receiver up check the the two chassis mounted transistors that go to A11. Make sure they are not shorted.

Also once you let the cell and lamp ovens warm up and the meter readings drop down you should test the transistors leakage. I just clip a resistor (500 Ohms or so) across the thermistor pins on A11 and make sure that each oven will completely shut off (meter drops to zero).

Corby,

For the lamp assembly, the 1.33k resistor is open circuit and I replaced with a 1.3k 1% one. I also replaced the 10 ohm on the stand off although the measurement is fine.

The 5MHz osc response to the EFC from the front panel and I mange to make it as close as possible to 5MHz

[5065AGuru]

Stanley.

You can apply +20Vdc to the lamp assy when it out of the unit and make sure it starts. Should draw about 140mA and after the lamp starts it drops down a bit.
The lamp should light within a minute or so cold and it will look pale whitish/purple.
If you pull a hot lamp assy out of the oven with power applied it should be deeper purple.
Sounds like the Quartz oscillator is OK!

Good luck

[syau]

Corby,

RVSP post repair photo:



For the lamp heater, I am using 11’ of wire, end up to around 52ohm, LOCTITE SI 5145 is used to secure the lamp heater into the RVSP which I purchased from RS.

[syau]

Stanley.

You can apply +20Vdc to the lamp assy when it out of the unit and make sure it starts. Should draw about 140mA and after the lamp starts it drops down a bit.
The lamp should light within a minute or so cold and it will look pale whitish/purple.
If you pull a hot lamp assy out of the oven with power applied it should be deeper purple.
Sounds like the Quartz oscillator is OK!

Good luck

The lamp drawn around 150mA (reading from the uncalibrated power supply) after start, 160mA when cold.

[syau]

Corby,

Found A11 Q4 open circuit, lucky same transistor being used on the battery charge A2. 

Temporary fitted the RVFR and power up the unit. Cell oven drop to 30  and lamp over drop to 38 after an hour or so. Photo I show around 23 but 2nd harmonic has no reading.

Should I leave it on for a while or follow your procedure to connect a 5vdc and a 5 ohm 10W resistor to the TED and try to de-flood the cell ?

BRGds/Stanley

[5065AGuru]

Stanley,

You need to scope TP2 on A7 and then in open loop tune thru C.F. using the fine quartz.
If you don't see a signal as you move plus minus .3 HZ then the cell might be flooded.
Unfortunately I don't think your unit has a TED! The very early units did not have it.
If you have a black/red twisted pair coming out of the receiver cylinder at the rear along with the cable going to the A7 input you have a TED. If not we will have to proceed differently!

Cheers,

Corby

[syau]

I am not able to get a signal on A7 TP2 when I move the freq +/- .3Hz so likely flooding occurred. I did some testing on the A7 by disconnecting the J1 and touch the center conductor and the circuit works.

My RVFR did fitted with TED. I will try to use a sourcemeter to apply 1A.





 

[dietert1]

As i never had this problem with our FE 5680A rubidium oscillators, can anybody write a sentence or two what is meant by "cell flooding"? The HP 5065a service manual used this term without explanation.

Regards, Dieter

[syau]

I am not able to get a signal on A7 TP2 when I move the freq +/- .3Hz so likely flooding occurred. I did some testing on the A7 by disconnecting the J1 and touch the center conductor and the circuit works.

My RVFR did fitted with TED. I will try to use a sourcemeter to apply 1A.

(Attachment Link)

[bsdphk]

The cell in the the 5065 is very different from those in small telecoms Rbs, in particular it has "too much" Rb in it.

This surplus Rb is supposed to freeze in a small "arm" on the side of the bulb, and a thermo-electric cooler ("TEC") lowers the temperature a tad to make that happen.

I belive the original idea was to make sure there were enough Rb to provide vapour saturation also after many years where some of the Rb was absorbed into the glass.

[5065AGuru]

Stanley,

I usually apply 5VDC through a 5 Ohm 10Watt resistor to provide the 1Amp TED current.
Leave the entire unit powered up with the 1Amp applied for a 5 or six days.
If you still can't see a signal other stuff needs checking, this can all be done while the 1Amp is applied to the TED.
-Turn the two top pots on A3 max CW
-what's the TP2 DCV reading on A3
-what's the synthesizer frequency reading
-What is the amplitude of the 137Hz out of A8. (across the chassis mounted mica cap)
- Watch A7 TP2 with a .25Hz offset on the 5Mhz output and adjust the A3R40 (pot on the side of A3) through its range and see if a signal appears.

Cell flooding is where too much Rubidium enters the resonance
cell and blocks the light.
Usually after a unit has been in extended storage or storage at elevated temperature.
This is mainly a 5065A problem although older Varian V4700 and R20 units
also can be effected.
The procedure in the manual cools the tip of the stem and collects the
Rubidium back where it belongs!
This takes about a week and then after reconfiguring the TED back to
normal cooling levels another week to stabilize the Rubidium level in the
cell. Modern telecom units utilize starved cells and don't have this problem.
Normal TED operation regulates the proper level of Rubidium in the cell.

Cheers,

Corby

[syau]

Hi Corby,

Made some measurement on A3

P2 - 5MHz, 7.76Vp-p
P1 - 136.6Hz 180mVp-p
TP2 - 393mV 
J8 - 60MHz 20mVp-p

Looks like the AGC not working, I removed Q4 and it measured fine, so as C12.

BRGDs/Stanley

[syau]

Hi Corby,

After battle for an hour, found Q2 D-S open circuit, I relocate Q5 over and then substitute Q5 with a J304 FET (I only have this on hand).

J8 output jump back to 5.52Vp-p

Will take some break and continue tomorrow.

BTW, any replacement suggestion for 1855-0327 (2N4416 ?)

BRGds/Stanley

[5065AGuru]

Stanley,

While watching A3 TP2 adjust the A3R40 (pot on the side of A3) max CCW and then turn CW and see if you can get a voltage of 4 to 5 VDC. (the first peak if you see peaks)

Then look at A7 tp2 in open loop while tuning fine Quartz plus minus .25HZ (at 5Mhz) and see if you get a 137Hz signal at the extremes and 274Hz when on frequency.

I've only used the 2N4416, not sure what an ideal replacement is.

The main thing is to find the signal, if it can be seen at all then the other parameters can be aligned to maximize the signal.

If still no signal we will have to try some more tests.

Do you have an HP8660 or HP3325A?

Cheers,

Corby

[syau]

I ordered some 2N4416 from Mouser (leaded version, not cheap) but forgot to change the shipping address to my home. Due to work from home policy, I can only back to the office next week to collect it. 

Yes, I got a 3325B, will dig it out from storage and test it.

[syau]

I ordered some 2N4416 from Mouser (leaded version, not cheap) but forgot to change the shipping address to my home. Due to work from home policy, I can only back to the office next week to collect it. 

Yes, I got a 3325B, will dig it out from storage and test it.

Replacing the 1855-0081 with 2N4416 improved the situation but not fixing it. Digging through the service manual found the equivalent is 2N5245. Found some NOS from evilbay and after replacing all the 1855-0051 with 2N5245 all level back to specification including the TP2 voltage (4.7V).



When I fitted back the A3 to the unit, I accidentally crushed 1 SMB jack 

[5065AGuru]

Stanley,

Hi! I can send a couple SMB if you would like?

Have your run the TED for a week?

When the lamp oven is warmed up did you happen to observe the lamp color by pulling the lamp assy out while still hot? I'm concerned about the color of your cold lamp in the picture.

Did you measure the lamp ovens temperature after the repair? (Did you use the original thermistor?)

If your 60Mhz looks OK now can you see a signal yet when you adjust the Quartz fine frequency across resonance at A7TP2?

What is the frequency and amplitude of the synthesizer output?

If you measure with an ohmmeter set to test semiconductor junctions both ways the 60Mhz input jack to the optical unit do you show a junction in one of the directions? 

If still no A7 TP2 signal we have to try testing the optical unit via an external signal.

Did you dig up the HP 3325B?

What synthesizer thumbwheel setting as shown on the optical unit label?

I'll need to try this on the unit I have on the bench  and once I get the details straight I'll post instructions.

Cheers,

Corby