Help repair E3631A - Unreg

[eevblogfan]

Hey

So I got one for repair , and I am willing to try and repair it , But I need your help here

the supply start fine , all the segments are turned on when powered on , but after that . the display is pitch black ,
when pressing "recall" the display show "Unreg"  , but nothing more !

so I did self test based on the service manual you press any key *BUT the Erorr key * for more then 5 sec .

and so I did , the supply beep once , mean it's starting with self test right ?
then I am waiting for the second beep . but he doesn't appear.

does any one know the problem's rooths ?

thank you

 

[Paul Price]

I don't have a clue what this E3631A type of equipment is, you might have revealed this mystery in your information hding posting. What troubleshooting is about, it to take the first step and to take the case apart and give it a visual inspection. You might be lucky and find some capacitor that is showing a bulge at its vent, or a burnt component. Without a schematic, you might still be able to find some points on the circuit board showing the power supply voltages which you then check.

[eevblogfan]

hey

I have the schematics

I also torn the thing apart

there are few "bodg" tantalum caps here and there . I may upload pics when I will be able to

that's Power supply , (+/-) 25V-1A plus 6V-5A

can it be the Digital portion ? 

since that supply don't response . and don't complete self test but telling me "UNREG" 

nothing obvious visually , no caps and no blowed parts

[Paul Price]

Since  my last reply, I have downloaded the service manual.

The first step is to use a scope, if you have one, or a DVM otherwise and check all the power supply voltages for their indicated voltages  and especially for noise and ripple. These points are clearly shown on the schematic.

If you find that they check ok, it might be some problem, even with the 8051 MCU related circuit, but there are also I see, many other more likely possibilities, many other components that are very much more likely to fail, such as optoisolators or discrete transistors to check.

First check the power supply voltages and let me know if any of the +15. +1.2 +5. -15. -1.2 power supply voltages are  out of spec.

[eevblogfan]

Hey

U26 is over heating

the supply rails :
I can't find the correct points . they are not marked on the board

the display is working simply when power on , so I guess the +-15V are good

the fan is working so I think the 12V are okay

and the 2.7V is tested and good

[Paul Price]

U26 might be the trouble it should not get hot. Can you check or replace that device, it is a TL074, a fairly common device.

First check Q8 and Q7. one or both might be  shorted.

[Paul Price]

Look at page  98 (manual page number not adobe ready page number) of the manual. It clearly tells you where the points are to measure all the power supply bias voltages.

[eevblogfan]

Hey

All voltages are good

any idea ?

the U26 is  70C+

[free_electron]

main CPU is down.

on the top board ( if you open the lid : the board that moves with the lid )

check the fuses right next to the power cable coming from the transformer.
next , check the tantalum capacitor on the right hand side next to the heat sink ( inbetween the to220 chips ) check for an exploded capacitor in that area.

check that you have 5 volts on the 5 pin to22 regulator top right of that board.

if all that is good : power down the supply , pop the eprom out of its socket and check the soldering of the socket. pop eprom back in.
power up.

you should have display now.

at power up the segment test is done by the on bord processor of the display. it has nothing to do with the main cpu.
if the display clears after that the main cpu isnt talking.

the tl074 running hot is not good . if those are down the dacs don't work. most likely the a/d will be shot as well. the ad706 / ad711 will be dead

[gerrysweeney]

Hi,

I have repaired two of these PSU's in recent months.  If U26 is getting hot, the odds are good that the chip is toast, its a cheap TL074D so no big deal. Without metering around, and based purely on the fact that you are saying U26 is getting hot I would do the following...

1. Remove U26 from the circuit.
2. Remove and check CR22
2. Remove and check CR23
3. Remove and check Q8
4. Remove and check Q7
5. With Q7 and Q8 removed, use your multimeter in current mode and put between pin 3 of U27 and the rail that the collector of Q8 is connected to. This should read about 36mA. What you are doing here is checking that U27 is working (its a constant current source)

This should give you a good sense of whats wrong, I would guess that Q7 is toast, Q8 might be, CR23 possibly is too. They are all really low cost and cheap parts so should be easy to fix.  Good luck....

Gerry

[eevblogfan]

main CPU is down.

on the top board ( if you open the lid : the board that moves with the lid )

check the fuses right next to the power cable coming from the transformer.
next , check the tantalum capacitor on the right hand side next to the heat sink ( inbetween the to220 chips ) check for an exploded capacitor in that area.

check that you have 5 volts on the 5 pin to22 regulator top right of that board.

if all that is good : power down the supply , pop the eprom out of its socket and check the soldering of the socket. pop eprom back in.
power up.

you should have display now.

at power up the segment test is done by the on bord processor of the display. it has nothing to do with the main cpu.
if the display clears after that the main cpu isnt talking.

the tl074 running hot is not good . if those are down the dacs don't work. most likely the a/d will be shot as well. the ad706 / ad711 will be dead

Hey free electron . I did all mention above and the display is still off .

I do get my 5V .

no sign of blown caps .

[eevblogfan]

Hi,

I have repaired two of these PSU's in recent months.  If U26 is getting hot, the odds are good that the chip is toast, its a cheap TL074D so no big deal. Without metering around, and based purely on the fact that you are saying U26 is getting hot I would do the following...

1. Remove U26 from the circuit.
2. Remove and check CR22
2. Remove and check CR23
3. Remove and check Q8
4. Remove and check Q7
5. With Q7 and Q8 removed, use your multimeter in current mode and put between pin 3 of U27 and the rail that the collector of Q8 is connected to. This should read about 36mA. What you are doing here is checking that U27 is working (its a constant current source)

This should give you a good sense of whats wrong, I would guess that Q7 is toast, Q8 might be, CR23 possibly is too. They are all really low cost and cheap parts so should be easy to fix.  Good luck....

Gerry

hey gerry

I have hot air work station in the job , so I may borrow her for that task . until then I have nothing to do with the SMD parts ...

[gerrysweeney]

@eevblogfan, an easy way to remove the TL074 without a hot air gun is to use fine side cutters and snip each pin right by the chip body, remove the chip body then de-solder the remaining pins from the board with a soldering iron, clean up with some solder wick. Easy and fast....but be careful not to lift tracks

Gerry

[Paul Price]

I think Your CPU is working because you are getting the "UNREG" message from the CPU looking at the operation of the power supply, don't remove the TL074D until you check the two transistors I suggested. If either is shorted, this might be cause of the TL047D heating up or also caused the TL074 to fail.

If either Q7 or Q8 is shorted, remove them and if the TL074 doesn't get hot after that it is likely ok.

[free_electron]

If memory serves well the 'unreg' is a single bit annunciator on the display. When you press a key the local 8051 turns it on if there is no communication with the main cpu.

If the display, after the segment test, goes blank there is no communication with the main cpu. The selftest is handled by the 8051 on the frontpanel. At the same time another 8051 on the mainboard below initializes the serial and gpib and waits.

If no communication is established within a certain timeframe with the main cpu a long beep will be heard.

Im pretty sure the main cpu is not running. Something is holding it up.

Double check the eprom in the socket. Ive had supplies behave strangely that worked perfectly fine after pulling and reseating that chip. (Too much dust in the plcc socket. Clean the socket with a blast of air)

[eevblogfan]

Hey

free_electron :  that chip's socket is not the problem , I have cleaned the thing with IPA . with no success

and U26 Is still hot ...  only tomorrow I might be able to borrow the Hot air gun ,

[eevblogfan]

Hey

CR22 and 23 are good ( read 0.6V on diode mode )

I removed Q8 and 7 , Connected  wire on the pad for the collector , and by mistake connected the other wire to pin 3 of U26   

and yes I heard small bang ,and felt small plastic Hit my arm while powering on the PS ....

then I saw U27 and not 26 

I have no idea what harm have I done here ,

after that both , the Q7 and Q8's collector to pin 3 on U27 were 0mA ...

if that any matter . to pin 3 of U26 I got 2.6mA on both collectors to that point ..

thank toy A lot ! 

[gerrysweeney]

Hey

CR22 and 23 are good ( read 0.6V on diode mode )

I removed Q8 and 7 , Connected  wire on the pad for the collector , and by mistake connected the other wire to pin 3 of U26   

and yes I heard small bang ,and felt small plastic Hit my arm while powering on the PS ....

then I saw U27 and not 26 

I have no idea what harm have I done here ,

after that both , the Q7 and Q8's collector to pin 3 on U27 were 0mA ...

if that any matter . to pin 3 of U26 I got 2.6mA on both collectors to that point ..

thank toy A lot ! 

Eeekkk...

You need to take more care....sorry to state the obvious !  these things are hard enough to fix without adding more faults   You should look at U26 which will almost certainly be broken now....you should see if you can find where the plastic come from (top of U26???)

If I were you would be start with a meter and carefully work your way through the schematic.  Look very carefully at the schematic and determine your Ov reference points, they are not always obvious.

Gerry

[Paul Price]

You should easily see an IC or transistor that has divested itself of some of its clothing.

Check all transistors, diodes  with your DVM for shorts, you will soon find one or more.

[eevblogfan]

Hey

I got another one

this time he is working

But the meters are noisy . few digits off ' horrible noise , 4~7 count jumping +- there ..

the "display limit" is dead on , hence I may say the supply's control loop is okay ,

the output noise is 1.6mV or so .. 

[bingo600]

Hey

I got another one

this time he is working

But the meters are noisy . few digits off ' horrible noise , 4~7 count jumping +- there ..

the "display limit" is dead on , hence I may say the supply's control loop is okay ,

the output noise is 1.6mV or so ..

I had an E3610 jumping around like that.

One of the big caps near the Trafo was leaking "Goo" , i changed the cap and had to wash down the board 2 times with IPA , before the "Goo" was removed from the area around the opamps. Then it became stable.

/Bingo

[eevblogfan]

Pictures :