Thurbly Thandar Instruments (TTi) PSU quality ?

[BravoV]

Recently just bought an used TTi PL330QMD dual channels linear PSU (link) and have few questions ..


* Is it normal that TTi use CapXon electrolytic caps ? I mean "all", not just part of it, starting at the main control & logic board, down to the the bulk caps after the rectifier. Also these bulk caps are also 85 C rated, yeah, its well ventilated though, but 105 C rated should be better right ? CMIIW


* As it has 2 big step down transformers as 2 channels, the upper part of the iron core are left unsecured, is it fine leaving that like that ? As I'm not experienced enough, I thought these iron plates should be secured ? As the 50/60Hz will probably wiggling those iron plates when the transformer is loaded ? Or I'm worry too much ? 



Appreciate any comments on these if its serious, like will those CapXon leak in the future ?
Should I clamp & secure the iron core with two long nut and bolt each ?

Or any other comments or insights regarding this particular TTi psu will be appreciated. TIA



Photos of the questioned items attached below.

[iainwhite]

As far as the transformer goes, I think it will be just fine as it is. 
There are other photos of TTI supplies on the forum that show the same setup - bolts on on the bottom.   
(for example, here: tti-ql355t )

I think the other holes are probably to give the manufacturer the option of mounting the other way up in another application.
I guess if it really worries you, you could buy some bolts/nuts of the correct size and fit them yourself.

[T3sl4co1l]

The transformer's laminations are firmly packed into the winding bobbin, and glued with varnish.  Sometimes a flap will come loose and vibrate, in which case you can clamp/screw/glue it back down.

It's made of copper and iron.  There's no much to goof up. 

That regulator board is lovely... capacitors clustered around a heatsink.

I don't think CapXon is particularly bad, it's just a very popular brand, so is often found in poorly designed, cheap equipment.  Electrolytic capacitors are an age item regardless of who makes them, especially ones clustered around heat sources.

Keep an eye on it; if you see poor operation, extra ripple, wrong voltages, schedule a replacement.

Tim

[wraper]

I've only seen problems with Low ESR series of Capxon, KF and GF series particularly. 85^oC or 105^oC does not tell much about reliability, frankly.
When is this PSU made? 105^oC rated caps became a norm only in 2000s, bulky snap in capacitors are still 85^oC rated in most cases.

[BravoV]

As far as the transformer goes, I think it will be just fine as it is. 
There are other photos of TTI supplies on the forum that show the same setup - bolts on on the bottom.   
(for example, here: tti-ql355t )

I think the other holes are probably to give the manufacturer the option of mounting the other way up in another application.
I guess if it really worries you, you could buy some bolts/nuts of the correct size and fit them yourself.

Thanks for the link, it looks like TTi deliberately did that, aren't they ?

Yeah, I will just find the suitable nuts & bolts to secure it.

[BravoV]

That regulator board is lovely... capacitors clustered around a heatsink.

You haven't seen this yet, check the attached photos below, top views of the PSU.

That tall black heatsink is also sandwiched between a 7805 and a power transistor that is driving the row of 6 2N3055s installed at the rear on the big heatsinks, its quite hot to touch even not fully loaded.

And that row of six bulk CapXon caps are also sandwiched between that black heatsink and the huge warm transformer, as you can see even its quite spacious inside, but all heat is dissipated only through convection, as there is no fan.

[BravoV]

I've only seen problems with Low ESR series of Capxon, KF and GF series particularly. 85^oC or 105^oC does not tell much about reliability, frankly.
When is this PSU made? 105^oC rated caps became a norm only in 2000s, bulky snap in capacitors are still 85^oC rated in most cases.

If you watch closely the 3rd and 4th photos, those small CapXons that are on main control board are 105C rated.

There is no clear manucfatured date, but from the ICs at the main control board, the latest date code is on 2001.

[Jay_Diddy_B]

Hi,

If you add bolts to the transformer, they should have an insulating washer. This is called a shoulder washer:



I think I can see the insulators at the bottom.



Regards,

Jay_Diddy_B

[BravoV]

If you add bolts to the transformer, they should have an insulating washer. This is called a shoulder washer:

I think I can see the insulators at the bottom.

Noted, will find the suitable washers for it, yes, I also noted that is has shoulder, not just plain flat O ring, as it will positioned the bolt to stay in middle and not touching the inner part of the iron plates, thanks Jay, really missed that important details. 

Just curious, what happened if the nuts & bolts are touching the two outer plates as its conducting them ?

Or ... say I use a fat tight fit bolt that somehow is touching the plates in the middle, not the outer ones ? Lower efficiency ? Heated ? Else ? 

[BravoV]

Attach photo below, the top terminals are primary windings that are connected to mains, while bottom ones are secondary windings, and three terminals on the right side are low current auxiliary power for the control and logic circuit.

Whats the purpose of the orange film cap 220nF 250V that is soldered directly at the secondary terminals (two yellow wires) that goes to the main power rectifier ? As I can't see it at the schematic (attached below), maybe they have not update it yet ?

[T3sl4co1l]

Probably EMI suppression from rectifier recovery.

Tim

[wraper]

If you watch closely the 3rd and 4th photos, those small CapXons that are on main control board are 105C rated.

And if you look on them too, there is no temperature rating visible.

[BravoV]

Probably EMI suppression from rectifier recovery.

Thanks, learned one thing today, noted, didn't know the EMI from the diodes recovery also can be a problem at this low frequency. 

[BravoV]

If you watch closely the 3rd and 4th photos, those small CapXons that are on main control board are 105C rated.

And if you look on them too, there is no temperature rating visible.

Sorry, yeah, its a bit vague as the picture was shot at very narrow angle, trust me, its 105C rated.

[SeanB]

Linear power supply, so most of the heat is in a load of TO3 parts on a big piece of aluminium, the rest of it is not going to be as hot, and in any case those capacitors likely are never going to fail in under 20 years, low ripple current, 100Hz ripple so low heating in the ESR ( no twenty thousand cycles a second of heat from charge and discharge, only 100 longer pulses) and the regulator heatsink is only going to be moderately warm, certainly not adding much to the ESR generated heat.

Transformer is vacuum impregnated, like a million microwaves a year are, and will not vibrate unless you disturb the bolt geometry by adding extra bolts. Those lower mounting bolts will have both a shoulder washer to insulate the bolt so it does not make a shorted turn with the small external field, and will have as well an inner insulation sleeve, either kraft paper that was varnished with the transformer, or a silicone impregnated glass fibre sleeve over the long bolt, again so there is no shorted internal turn, which here is worse as it will create a significant field imbalance in the core as well, and will really heat up the core. essentially leave it alone and it will be quiet. The holes are a part of the manufacture of the E and I laminations, there mostly to align them during manufacture and used as a convenient and cheaper than a core clamp mounting method.

If you want to replace all those caps in 5 year do do, but they will last pretty long there, many a linear supply still works after decades of use with those caps, and there I often see them being toasted by both putting the output transistors on the case as heatsink, being right next to the bridge rectifier diodes with them being underspecced as well, and next to a transformer being run at a point well in saturation core wise and with winding losses being very high to cut the mass of copper and iron in there. Basically living in an oven 24/7/365, and it still is running well enough a decade later.

[Towger]

There are at lest 3 or 4 versions of these over the years with different PCBs.  Yours is one of the newer ones.   On at least one version there is a 220uf 16v cap at the edge of the PCB, which from memory feeds power to the multi plexed LEDs. These leaked badly and were well below spec on mine. You will not see it unless you remove them. 

[BravoV]

Linear power supply, so most of the heat is in a load of TO3 parts on a big piece of aluminium, the rest of it is not going to be as hot, and in any case those capacitors likely are never going to fail in under 20 years, low ripple current, 100Hz ripple so low heating in the ESR ( no twenty thousand cycles a second of heat from charge and discharge, only 100 longer pulses) and the regulator heatsink is only going to be moderately warm, certainly not adding much to the ESR generated heat.

...

If you want to replace all those caps in 5 year do do, but they will last pretty long there, many a linear supply still works after decades of use with those caps, and there I often see them being toasted by both putting the output transistors on the case as heatsink, being right next to the bridge rectifier diodes with them being underspecced as well, and next to a transformer being run at a point well in saturation core wise and with winding losses being very high to cut the mass of copper and iron in there. Basically living in an oven 24/7/365, and it still is running well enough a decade later.

Hi SeanB, glad to see you here.

Yes, thanks, I'm aware of this low freq 100/120 Hz and low ARMS these bulk caps experienced during operation.

Its just I am worry of cap leaking. Does CapXon known for that ?

Transformer is vacuum impregnated, like a million microwaves a year are, and will not vibrate unless you disturb the bolt geometry by adding extra bolts. Those lower mounting bolts will have both a shoulder washer to insulate the bolt so it does not make a shorted turn with the small external field, and will have as well an inner insulation sleeve, either kraft paper that was varnished with the transformer, or a silicone impregnated glass fibre sleeve over the long bolt, again so there is no shorted internal turn, which here is worse as it will create a significant field imbalance in the core as well, and will really heat up the core. essentially leave it alone and it will be quiet. The holes are a part of the manufacture of the E and I laminations, there mostly to align them during manufacture and used as a convenient and cheaper than a core clamp mounting method.

Ok, won't touch that two big transformers, your explanation makes sense, thank you. 



Another question regarding mechanical, the top case is secured using this screws and the black thingy metal tabs, sorry, don't what its called. I live in tropical and quite humid climate, as you can see at the close up photos (attached below), the black steel thingy is starting to rust.

As the whole power supply relies on these securing points, is there anything I can do to stop or at least slow down the rust ? I think these can be pulled out easily though.

[BravoV]

There are at lest 3 or 4 versions of these over the years with different PCBs.  Yours is one of the newer ones.   On at least one version there is a 220uf 16v cap at the edge of the PCB, which from memory feeds power to the multi plexed LEDs. These leaked badly and were well below spec on mine. You will not see it unless you remove them.

Yes, finally, someone who knows this TTi PSUs well enough. 

Thanks for the warning, this is my biggest worry, leaking caps. 

Attached the photo of the control board (master), "all" electrolytic caps are CapXon, is it common for TTi PSUs ?

Also do you think its better replace them all ? Especially looking at your own experience.

Btw, which cap at the edge is that ? Could you point out at the attached photo below ?

[SeanB]

Rusting tabs are easy, a wipe over front and back with a cloth soaked in oil will stop that.

[Towger]

I replaced all of mine, but it was a older version (early 90s) and did not used the same make of caps.  It was also a lot ruster than yours, i think it was stored outside on a shed for years.  Looking at the photo, it is the cap at the left edge of the PCB, below the LED. I think it it is the only 220uf cap on the board.  Some of the small caps on  the bottom left also showed signs of leaking (dried whitish residue) at the bottom when removed, but tested fine. Remember your pcb, may be by quite different.
I did not bother to test my theory, but i think the cap is exposed to some AC from the multiplexing of the led display, which would be quite hard on it.

[BravoV]

Rusting tabs are easy, a wipe over front and back with a cloth soaked in oil will stop that.

Ok, I think I will detach all those tabs, wipe clean and dunk them all into the oil for a while, and attached it back in slightly wetted/damped condition by the oil (no dripping).

As I'm worry the underneath the folded tab is also rusted.

Thanks SeanB.

[BravoV]

I replaced all of mine, but it was a older version (early 90s) and did not used the same make of caps.  It was also a lot ruster than yours, i think it was stored outside on a shed for years.  Looking at the photo, it is the cap at the left edge of the PCB, below the LED. I think it it is the only 220uf cap on the board.  Some of the small caps on  the bottom left also showed signs of leaking (dried whitish residue) at the bottom when removed, but tested fine. Remember your pcb, may be by quite different.
I did not bother to test my theory, but i think the cap is exposed to some AC from the multiplexing of the led display, which would be quite hard on it.

Decision made, all CapXon elcaps at the control board will be replaced with Japanese ones.

Btw, do you remember the leaking caps, what brand was it ? CapXon too ?

Although I don't have any plan to replace the big bulk caps at the driver/rectifier board yet, do you have any experience at that part ?

Talking about the 7 segment led muxing, one of the segment at the slave board is dead, not a big deal though and its fully functional, its just annoying to see that every time. 

Thanks Towger. 

[Towger]

At work now.  All the caps were ELNA rated at 85 degrees.  I replaced them all with a mixture of Rubycon and Panasonic 105c, cost more than I got the PSU for!  The rectifier caps went to the junk box, the others to bin.  Looking at my notes, the bad cap on both channels was 220uf 10v.  I put a 25v on in its place, which was slightly too big to fit correctly.

2 out of the 4 LED displays on mine had bad segments, the displays are an old standard size.  I bought replacements on ebay, they were not an exactly (visual) match, the 4 digits are made up from 2x2 digit units, but were otherwise compatible:  NSC NSB-5881 Multilexed DISPLAY RED LED MODULE 4-DIGIT 7 SEGMENTS Numeric 0.5INCH

The led dies in the displays are bonded directly to the PCB, with just the plastic cover as protection, so are exposed to damp. The bad displays were both voltage, so near the leaky capacitors...

BTW: I think the designer of these (or some versions) is a forum member.

BBTW: Does anyone have an cheap source for the ALPS pots, they are a old size. Mine were dirty but improved after cleaning, on seconds thoughts replacing them with multi turn pots would be a better solution.

[SingedFingers]

You really don't need multiturns on those supplies. Coarse + fine is good. The current limit doesn't have the resolution or stability required for a multi-turn.

Farnell stocks the  pots I think, or did about a year ago when I replaced one on my PL310.

The older PL series supplies have a rather large expensive wirewound for the coarse control - think yourself lucky

Caps are fine in both of my PL supplies. One is 2004, the other is 1993. Newer one has nichicons in it. Might not be the first set it has had.

[macboy]

I agree that you don't need multi-turn pots for the current limit. VR5 has a logarithmic-like taper, making it easy to dial in a small current limit but still providing the full range on a single turn part.

You seem keen on fixing it up, so you might care to know that you can likely remove the yellow patina from those knobs using high strength peroxide and sunlight. Google retrobright, and check out some posts like this and this in another thread, where member TiN and I each restore front panels of expensive Keithley 2001 meters. As they are now, those  yellowed knobs are a real eyesore.