Topward 6603A Linear Power Supply Teardown

[AlphZeta]

Here are some teardown pictures of the Taiwaness Topward 6603A (dual 60V 3A and 5V 5A, CC, CV, Independent/Tracking/Parallel/Series) I bought from eBay:

This particular unit was made in 97. The oscilloscope images corresponds to the power-on characteristics of

1. no load maximum output voltage
2. no load lowered output immediately after maximum output voltage
3. load under CV
4. maximum load under CC

From the build and the power-on characteristics, it appeared to be a pretty good unit. I have a more in-depth review on my site (http://www.kerrywong.com/2012/12/01/topward-6603a-linear-power-supply-teardown/).

[Shuggsy]

Nice! Looks like a pretty good unit. About the only complaint I've had about the (quality) far east supplies is that the soldering/assembly can sometimes leave something to be desired. Usually that's a quick fix if you take it apart and examine any offending bit. This one looks to be well built and easy to service if needed. Very cool! Nice scope captures, too!

Love the analog meters.

[saturation]

A nice supply, its well made, Taiwan stuff is, by name alone, likely very good .  The brand is not familiar but ebaying it I find its a pretty prolific in the used market.  Its a name worth remembering for the future.

[T4P]

About the only complaint I've had about the (quality) far east supplies is that the soldering/assembly can sometimes leave something to be desired.

Huh? The soldering is fantastic and i've seen american made stuff soldered WORSE. Well actually taiwanese even these days and those days take pride in their stuff and didn't attempt to cut cost left and right

[ptricks]

soldering looks okay, they could have cleaned the flux off the board though. The only thing that really bothers me about that supply is the organization inside the case, too many wires for what the circuits are doing like someone just added boards and if it didn't fit here, they said'  oh we will just stick it here' . The wiring setup will make troubleshooting problems a pain.

[AlphZeta]

soldering looks okay, they could have cleaned the flux off the board though. The only thing that really bothers me about that supply is the organization inside the case, too many wires for what the circuits are doing like someone just added boards and if it didn't fit here, they said'  oh we will just stick it here' . The wiring setup will make troubleshooting problems a pain.

Yeah, the wiring is a bit messy. But most of the wires are from the 5 TO-3's and the interconnects among the boards. The reason for this design, I believe is that since Topward's 6000 line of power supplies all share the same chasis, they modulized the circuits so that they can easily swap out different boards for different power supplies (6603A, 6302A, etc).

But most of the wires are neatly tied together in groups.

[AlphZeta]

Just a quick update. I sent a request to Topward's for a copy of their service manual after I received the unit. They quickly sent me one free of charge. It seems that they really value their customers which really says a lot about the company. A big thumbs up!

And after reviewing the circuit diagrams, it appeared that they do reuse the same boards in different models whenever applicable and thus validated my speculation as to why they chose to break it down into so many boards in their design (which contributed to the "messy" wiring).

[rikkitikkitavi]

Just wanted to add that I have a broken Topward 6303D. Did send an email,and got a reply with attached schematic within an hour (9am GM+1, aka late in Tawian)

That is truly amazing customer support in my regards

/Rickard

[sotos]

Thumps up

 Some other company’s tell you to sent it to them for service or buy a new one, just because you asked for a service manual.

[anton74]

Dear all,

I have a Topward 33010D power supply that does not work.  The PCB layout is similar to that on the picture of AlphZeta above.  I think that two Zener diodes that are close to the 741 opamps on the left and the right side of the PCB should be replaced.  However, I cannot read the markings of these zener diodes.  Does anybody knows the specifications of these zeners?

Thanks.

[AlphZeta]

Those are not Zener diodes, they are just 1N4148's for clamping the input into the OpAmp.

[anton74]

Those are not Zener diodes, they are just 1N4148's for clamping the input into the OpAmp.

I thought these are zeners since on the PCB they are labeled as ZD1 and ZD2 while other diodes are labeled as D1, D2, etc.  Are there any zeners on the board of 6603A?  I asked Topward for the service manual but did not receive any answer. 

[AlphZeta]

Maybe I was looking at a different TL084. What's the IC number where the diodes were located? I can take a look for sure if you can check just make sure we are looking at the same diodes.

[free_electron]

these are pretty good supplies. they are the OEM for the older tektronix supplies.

but like many taiwanese they suffer from the 'lets see how many miles of wires and connectors we can cram into this design

[anton74]

I encircled 3 diodes on your picture, I think the ZD1 on my board corresponds to the encircled diode on the left side of your PCB, while the ZD2 is probably one of the two diodes on the right side of your PCB.

Thanks a lot.

Anton.

[AlphZeta]

Yep. @free_electron, these supplies are pretty difficult to service. The two boards on the front panel are soldered together and removing a board requires desoldering all the banana plugs.

[AlphZeta]

OK, the left one (CR13) is a 9.1V Zener, the one on the top to the right CR 15 is 1N4148 and the one under it is CR7, a 5.1V Zener. But that's for the 6603A though, It's likely they are different for your 33010..

[anton74]

Thanks.

[anton74]

AlphZeta, could I ask another question?  What are the components responsible for the voltage regulation?  I replaced the zeners, the power supply started to work, the current regulation seems OK.  However, the voltage regulation does not work - the voltage is not affected by the potentiometer.

Thanks.

[lowimpedance]

So what is the value of the measured voltage ?.
Could be a shorted pass transistor, usually at the rear on heat sinks and be a TO3 package. (2n3055 perhaps)

[anton74]

The voltage is high and not stable,  not responsive to the voltage adjust potentiometer.  Also, one of the resistors (R12, 100 Ohm) is getting very hot.  I thinks this resistor corresponds to R24 on 6000 series PS.
There are 4 power transistors, 2N3772. 
Could it be the TL431 shunt regulator?

Anton.

[AlphZeta]

The voltage is high and not stable,  not responsive to the voltage adjust potentiometer.  Also, one of the resistors (R12, 100 Ohm) is getting very hot.  I thinks this resistor corresponds to R24 on 6000 series PS.
There are 4 power transistors, 2N3772. 
Could it be the TL431 shunt regulator?

Anton.

I fixed one 6603A (not the one I did my original teardown with) a while ago and that one was showing similar symptom as yours did. The output of one channel would be at 70V all the time regardless of what the pot was set to. At first I thought it was power transistors as well, but it turned out it was one of the 2SC1384's (C-E shorted) and I changed it with a BD137 and everything worked great afterwards.

Since it's fairly easy to remove the 2772's (they are connected via connectors) from the circuit, you can easily figure out whether it's the 2772 or something else. But that should be a good place to begin trouble shooting.

[anton74]

Well, it seems that I found the problem.  The previous owner probably did a modification: I found that a PCB trace that is going from the "Voltage" potentiometer is cut!  There are 3 wires that soldered to the PCB contacts of the "Voltage" and "Fine" pots to the rear of the unit to the round DIN5 connector.  I think the user did this mod in order to use an external potentiometer to control the voltage. The previous and the current users utilized this unit as a voltage source for the microscope lamp (in the research labs).  However, the current user do not use any external potentiometer, so the unit was actually working but only the "Current" potentiometer was functional and was used for brightness control.  It seems that in this mode one of the 100 Ohm resistors and one zener (5.1V) overheated, and finally damaged.  After replacing the resistor, zener (I used 5.6V) and repairing the PCB trace that was cut, the unit works, both current and voltage are adjustable.  The resistor and zener do not overheat anymore.  I think the voltage reading of the display have some fluctuations when the load (24V 6Watt lamp) is connected to the output, should it be so?  The 3000 series could produce up to 30V and up to 10A, so with the above load at 24-25V I am getting about 0.25-0.3A and the "Current" is fully cranked to the maximum. Theoretically, you cannot get more current (6W/24V = 0.25A; the resistance of the load is pretty high - 24V/0.25A = 96 Ohm), the voltage is nearly maximal.  When the outputs are shorted, I can get about 10A at 30V.  So, do you think these readings are normal?

[AlphZeta]

I think the voltage reading of the display have some fluctuations when the load (24V 6Watt lamp) is connected to the output, should it be so?

Depending on how much. Topward 6 series (and 3 series I  believe) have very tight load regulation (<0.01%) so anything more than a few mV under that light load would be out of spec. Don't know if you can find a 5.1V Zener and give it a try as 5.6V is probably over what the circuit can properly compensate via the onboard pots.

[anton74]

I think the voltage reading of the display have some fluctuations when the load (24V 6Watt lamp) is connected to the output, should it be so?

Depending on how much. Topward 6 series (and 3 series I  believe) have very tight load regulation (<0.01%) so anything more than a few mV under that light load would be out of spec. Don't know if you can find a 5.1V Zener and give it a try as 5.6V is probably over what the circuit can properly compensate via the onboard pots.

Well, I changed the zener to 5.1V.  The voltage display is fluctuating a lot.  However, the actual voltage at the outputs is stable and reasonable, when measured with a voltmeter.  Also, the voltage entering the display board is OK.  Something wrong on the display circuit?  There are two big chips, A/D converters, ICL7107SCPL and two HA17431's.  The HA17431 are probably OK, I tried to swap for another ones (TL431) without any effect.  The A/D converter is bad?  Its power supply (two +5V)?  Two 7805 regulators produce 5V when the display board is disconnected; when connected, one measures 4.6-4.7V, another one is 4.3-4.4V.  Their corresponding diode bridges are somewhat warm.  What else it could be?