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2246 power supply

 

I had posted about my 2246 scope a few days
ago but have had no replies.

I have the feeling the 22xx power supplies issue
has been covered and maybe people are tired of it?

I am poor with the Yahoo group search function.
I have been able to dredge up that capacitors
and the ZS/ZM diodes are to be replaced and
that sometimes a transformer fails.

The symptoms I have are that I am in chirp mode
if the main board is attached.

Without the main board the scope will come up but
my cheapie volt meter reads -41VDC when I go
black to the chassis and red to the 43V TP on the power
supply board.

I do have a lot of the black ZS diodes. I have changed
out all the silver colored, grounded case electrolytics.
I have not changed out the big initial electrolytic or a
couple of small ones.

Any advice for me?
 

I do not own a 2246 so cannot give specific advice.? I am especially unfamiliar with what is meant by the "43V TP on the power supply board".? But I will point out there are two separate "grounds" in a transformer coupled switching power supply as used by Tektronix.? The side that connects to the mainboard uses the chassis as ground.? But the switching side does not.? I suspect the "43V TP" does not use chassis as ground.? So measurements between there and chassis will not make sense.?

Also, take note that measurements on the "high side" of a switching supply can be dangerous if you do not use an isolation transformer and/or battery operated test gear.

Finally, tick mode is usually caused by current overload.? Since the inverter runs when the mainboard is disconnected, it sounds to me that you have an overload on the mainboard.? But it would take more testing to verify this theory.? Unfortunately, I?lack the knowledge to help here.

Finally, the group search function is simple enough to use.? At the top of the group home page is a box to enter a search term to "Search Groups".? Once you search on a term, any term, you will get a second page.? Near the top right of that second page is another?selection for "Advanced Search" where you can provide many more search terms and narrow your results.? The advanced search will search the entire group?and is not influenced by your original search.???

Hope this helps.

From: Chris Howard
To: TekScopes@...
Sent: Saturday, January 25, 2014 5:42 PM
Subject: [TekScopes] 2246 power supply

?

I had posted about my 2246 scope a few days
ago but have had no replies.

I have the feeling the 22xx power supplies issue
has been covered and maybe people are tired of it?

I am poor with the Yahoo group search function.
I have been able to dredge up that capacitors
and the ZS/ZM diodes are to be replaced and
that sometimes a transformer fails.

The symptoms I have are that I am in chirp mode
if the main board is attached.

Without the main board the scope will come up but
my cheapie volt meter reads -41VDC when I go
black to the chassis and red to the 43V TP on the power
supply board.

I do have a lot of the black ZS diodes. I have changed
out all the silver colored, grounded case electrolytics.
I have not changed out the big initial electrolytic or a
couple of small ones.

Any advice for me?
 

Surprised no ones helped you on this. On the 2246 its rare that the large 3 pin secondary electrolytics fail. The common fault causing tripping is C2210 (4.7uF), usually accompanied by failure of Q2209 or Q2210 (TIP32C are ok replacements if I remember right). Components around C2210 will look burned and overheated but are almost always ok. If you are unlucky Q2214 fails also. You can test the power supply out of the case using the fan as a load for a quick test. (Carefully!) Beyond those component fails, the switching transformer and multiplier can fail. (Disconnect the flying lead from the transformer to check the multiplier)
The secondary diodes also fail, 4 are schottky and show low on a test meter but are usually ok, the others should read the usual 0.6 or whatever your test meter shows for a standard diode.The 3 pin caps need to be low ESR, so if you bought standard caps I would put the originals back in as they are good quality caps.

Point of caution, if you run the supply on its own the 3 pins near the multiplier (tube heater) will retain a nice surprise for you long after powering off

If you are not familiar with switching supplies BE CAREFUL! They can be lethal. JC




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

I had posted about my 2246 scope a few days
ago but have had no replies.

I have the feeling the 22xx power supplies issue
has been covered and maybe people are tired of it?

I am poor with the Yahoo group search function.
I have been able to dredge up that capacitors
and the ZS/ZM diodes are to be replaced and
that sometimes a transformer fails.

The symptoms I have are that I am in chirp mode
if the main board is attached.

Without the main board the scope will come up but
my cheapie volt meter reads -41VDC when I go
black to the chassis and red to the 43V TP on the power
supply board.

I do have a lot of the black ZS diodes. I have changed
out all the silver colored, grounded case electrolytics.
I have not changed out the big initial electrolytic or a
couple of small ones.

Any advice for me?
 

Thanks!
I will check that out.

On 1/26/2014 3:39 PM, chipbee40@... wrote:


Surprised no ones helped you on this. On the 2246 its rare that the large 3 pin secondary electrolytics fail. The common fault causing tripping is C2210 (4.7uF), usually accompanied by failure of Q2209 or Q2210 (TIP32C are ok replacements if I remember right). Components around C2210 will look burned and overheated but are almost always ok. If you are unlucky Q2214 fails also. You can test the power supply out of the case using the fan as a load for a quick test. (Carefully!) Beyond those component fails, the switching transformer and multiplier can fail. (Disconnect the flying lead from the transformer to check the multiplier)
The secondary diodes also fail, 4 are schottky and show low on a test meter but are usually ok, the others should read the usual 0.6 or whatever your test meter shows for a standard diode.The 3 pin caps need to be low ESR, so if you bought standard caps I would put the originals back in as they are good quality caps.

Point of caution, if you run the supply on its own the 3 pins near the multiplier (tube heater) will retain a nice surprise for you long after powering off

If you are not familiar with switching supplies BE CAREFUL! They can be lethal. JC




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

I had posted about my 2246 scope a few days
ago but have had no replies.

I have the feeling the 22xx power supplies issue
has been covered and maybe people are tired of it?

I am poor with the Yahoo group search function.
I have been able to dredge up that capacitors
and the ZS/ZM diodes are to be replaced and
that sometimes a transformer fails.

The symptoms I have are that I am in chirp mode
if the main board is attached.

Without the main board the scope will come up but
my cheapie volt meter reads -41VDC when I go
black to the chassis and red to the 43V TP on the power
supply board.

I do have a lot of the black ZS diodes. I have changed
out all the silver colored, grounded case electrolytics.
I have not changed out the big initial electrolytic or a
couple of small ones.

Any advice for me?
 

Hi,

Believe it or not, I am finally diving back into my 2246.

The initial problem was clicking power supply on startup.

I replaced most of the electrolytic capacitors.
That didn't fix it. Following the advice given below
(for which I am very thankful), I replaced Q2209 and Q2210
with TIP31A. I have not replaced Q2214.

I attempted to fire it up after the Q2209/Q2210 replacement.

Now I am getting nothing. No voltages in the through-pins
in the center of the board. No fan, no relay clicks.
I do have voltage at the test
points labeled DC+ and DC- near the big C2202.


What do you think next, Q2214?

On 1/26/2014 4:45 PM, Chris Howard wrote:


Thanks!
I will check that out.

On 1/26/2014 3:39 PM, chipbee40@... wrote:


Surprised no ones helped you on this. On the 2246 its rare that the large 3 pin secondary electrolytics fail. The common fault causing tripping is C2210 (4.7uF), usually accompanied by failure of Q2209 or Q2210 (TIP32C are ok replacements if I remember right). Components around C2210 will look burned and overheated but are almost always ok. If you are unlucky Q2214 fails also. You can test the power supply out of the case using the fan as a load for a quick test. (Carefully!) Beyond those component fails, the switching transformer and multiplier can fail. (Disconnect the flying lead from the transformer to check the multiplier)
The secondary diodes also fail, 4 are schottky and show low on a test meter but are usually ok, the others should read the usual 0.6 or whatever your test meter shows for a standard diode.The 3 pin caps need to be low ESR, so if you bought standard caps I would put the originals back in as they are good quality caps.

Point of caution, if you run the supply on its own the 3 pins near the multiplier (tube heater) will retain a nice surprise for you long after powering off

If you are not familiar with switching supplies BE CAREFUL! They can be lethal. JC




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

I had posted about my 2246 scope a few days
ago but have had no replies.

I have the feeling the 22xx power supplies issue
has been covered and maybe people are tired of it?

I am poor with the Yahoo group search function.
I have been able to dredge up that capacitors
and the ZS/ZM diodes are to be replaced and
that sometimes a transformer fails.

The symptoms I have are that I am in chirp mode
if the main board is attached.

Without the main board the scope will come up but
my cheapie volt meter reads -41VDC when I go
black to the chassis and red to the 43V TP on the power
supply board.

I do have a lot of the black ZS diodes. I have changed
out all the silver colored, grounded case electrolytics.
I have not changed out the big initial electrolytic or a
couple of small ones.

Any advice for me?
 

Back at my long-time sick 2246

I've replaced 2209, 2210 and 2214.
Right now my symptoms are that I have no voltages at the large
feed-through connector. I have about 170 volts at the test
points marked "DC+" and "DC-" near diodes, I assume on the incoming
side of the supply.

The heat sink on Q2201 is warm (is that good?). The fan is not turning.

I am not getting any relay sounds, no sounds at all.

Any suggestions on what I should test?


Chris

On 1/26/2014 3:39 PM, chipbee40@... wrote:


Surprised no ones helped you on this. On the 2246 its rare that the large 3 pin secondary electrolytics fail. The common fault causing tripping is C2210 (4.7uF), usually accompanied by failure of Q2209 or Q2210 (TIP32C are ok replacements if I remember right). Components around C2210 will look burned and overheated but are almost always ok. If you are unlucky Q2214 fails also. You can test the power supply out of the case using the fan as a load for a quick test. (Carefully!) Beyond those component fails, the switching transformer and multiplier can fail. (Disconnect the flying lead from the transformer to check the multiplier)
The secondary diodes also fail, 4 are schottky and show low on a test meter but are usually ok, the others should read the usual 0.6 or whatever your test meter shows for a standard diode.The 3 pin caps need to be low ESR, so if you bought standard caps I would put the originals back in as they are good quality caps.

Point of caution, if you run the supply on its own the 3 pins near the multiplier (tube heater) will retain a nice surprise for you long after powering off

If you are not familiar with switching supplies BE CAREFUL! They can be lethal. JC




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

I had posted about my 2246 scope a few days
ago but have had no replies.

I have the feeling the 22xx power supplies issue
has been covered and maybe people are tired of it?

I am poor with the Yahoo group search function.
I have been able to dredge up that capacitors
and the ZS/ZM diodes are to be replaced and
that sometimes a transformer fails.

The symptoms I have are that I am in chirp mode
if the main board is attached.

Without the main board the scope will come up but
my cheapie volt meter reads -41VDC when I go
black to the chassis and red to the 43V TP on the power
supply board.

I do have a lot of the black ZS diodes. I have changed
out all the silver colored, grounded case electrolytics.
I have not changed out the big initial electrolytic or a
couple of small ones.

Any advice for me?

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