Fridge - Gram

[tmcw]

Have this fridge, laboratory grade unit, not working fully.

It's designed with a chilling unit at the top, on the inside, and a fan just below that. When the door is closed, the fan blows the cold air down through the fridge, and when the door opens, the fan switches off, presumably so that it doesn't blow all the cold air out.

The fan isn't switching on, so in addition to not having uniform cold throughout the fridge, the chilling tubes tend to ice up. I took the lid off the top, electronics are in the lid, and when the door is opened and closed, I can hear the relevant relay clicking.

Now, separate to the main electronics board, off a connector at the relay I can hear clicking, is a small 200-240VAC to 12VDC switching power supply, see photos. When the door is closed, on the input of the switching power supply, I have 230V, and when the door is open, it drops to zero. So far so good.

On the DC output of the switching power supply, door open, I have zero volts, but when the door is closed, I'm only getting about 3V, so not enough to power the 12V fan downstream of this switching power supply.

So, it looks like I've found the source of the problem. The 470uF/16V cap at the DC output is a bit bloated, I swapped it with an unbloated one from a donor board, but the output voltage actually dropped further.

The board has a couple of chips, a VIPer12A, and an 817CN. Is there anything else on there worth testing further? There is some gunk on the input side, but I think it's just some brown glue for holding the components during manufacture.

Would something like this be a suitable replacement? Description says it's for LEDs, but assume the input and output voltage is all that matters.

https://www.ebay.co.uk/itm/284961060022

[stj]

Re: Fridge - Gram

what make/series of cap did you fit?
it needs to be a low esr type for a switching supply.
also change the small one that starts up the chip

[tmcw]

Re: Fridge - Gram

Thanks for the reply.

I don't have any good caps to hand, so was just scouring some old boards for parts, and the bloated cap near the DC out, the only 470/16V I could find was a janky green Lelon, and it was worse than the bloated one as far as the voltage out was.

However, I took off the small one near the chip (22/50V, AISHI) and found an LXV on an old board, put it on, and the fan is now spinning when the door is closed!

In the first few seconds of powering up the fridge, I could see that the fan was jerking, not getting past the initial "hump" to help it get spinning constantly, just moving a couple of millimeters, back and forth. I quickly put the multimeter on the DC out, and the voltage was low, jumping around between less than one volt, and a few volts, but then all of a sudden, after maybe 10 seconds, the fan started spinning.

The voltage on the DC out is now changing between about 8.8 and 9.5 volts. That's just with the small 22/50v cap near the chip changed.

Anyway, big improvement. I'll see about getting a good 470/16V cap for the bloated one, but any point in changing the others, is it likely to bring the output back up around 12V?

I'll leave the fridge on overnight, and put a couple of thermometers in, and check in the morning.

Thanks again for your help.

[stj]

Re: Fridge - Gram

are the other 2 mains smoothing - 400v?
if they are then they are probably o.k. - but how old is this?

[redwire]

Re: Fridge - Gram

For the time, money and hassle I would shotgun it - replace all 4 electrolytic capacitors.
The reason is a fading cap can cause more damage, if it hasn't already- the VIPer12 might be damaged/weak. The 22uF cap is critical.
Where is this located? If it's inside the cooler then low temp parts need to be used.

It's also possible the fan is getting old and drawing more current. See if it needs lube or the brushes are worn out etc. I would check current draw, or a load test on the PSU in case the PSU is actually fine now.

[tmcw]

Re: Fridge - Gram

The fridge is about 11-12 years old, lab environment, opened and closed many times a day, more than the typical domestic fridge. It got down to 4oC within an hour or so, and stayed like that overnight. Fan going on/off with the door closed/opened, as expected. I've put it back in the lab for the time being, but will get new caps to shotgun the PSU.

The other 2 caps are 4.7/400V Su'scons (or something like that), haven't taken them off yet, but will definitely get good replacements for the other 2, there are a few other fridges with the same problem, so will get a stock of them. Given the age, and since I'm in there already, might just change all 4?

The electronics are all in the lid, so well insulated away from the cold of the fridge. The underside of the lid has a kind of waffle design, with the wiring threaded through gaps, and held in place with masking tape or polystyrene blocks.

The fan moves freely when running, no squeaking or squealing noises. I didn't get a chance to test the load, but will do so with the next one, and when I have the first one open again to replace the other caps.

Just to diverge a bit from the above problem, I've already gotten the next fridge, but it is giving an error F6 upon power-on, which when I look it up, I find that it might be...

"Error on low temperature protection sensor. Service is required."

I'm trying to figure out what this might relate to. The mainboard has 3 connectors that have 2-wire devices which I suspect are thermocouples, one goes to the radiator on the outside-back of the fridge, one goes to the tray under the chiller unit (near the fan), and the other one is stuffed into the fins/vanes of the chiller unit. I'm thinking the error might relate to the one stuffed into the fins of the chiller unit, as it's the one most likely to get coldest. Would that be right?

[tmcw]

Re: Fridge - Gram

Not sure now where the low temperature protection sensor will be now, as I disconnected all 3 connectors, and got errors F1, F2, F3 and F6 on the display, and plugging in each of the 3 connectors in turn eliminated the relevant error code, as per the error table attached.

F1 for the sensor in the tray, F2 for the sensor in the chiller, and F3 for the sensor on the radiator at the back, outside.

[stj]

Re: Fridge - Gram

if you replace the 400v caps, use rubycon LLE series

[redwire]

Re: Fridge - Gram

What make and model fridge is this, and the "next fridge" as well.

The temp sensors are likely identical thermistors, just take Ohmmeter readings on them to find the defective one. They go high resistance when cold, so a wiring open-circuit looks like too cold.
I'm not sure how 3 connectors correspond to the sensors. There's so many of them.

[tmcw]

Re: Fridge - Gram

The fridges are all the same, GRAM Biocompact II RR410.

I've attached a couple of photos, one of the mainboard, and one of two of the sensors that are inside the unit, one stuffed into the chiller, the other rests in the tray below the chiller. In that photo, you can also see the wiring that goes to the fan, which is attached to the tray.

When I was talking about the connectors, I was referring to the physical connector on the mainboard that the 3 temperature sensors attach to, the one hanging is connected to A on the mainboard, the one stuffed into the chiller is connected to B, and C is connected to a sensor that is cable-tied to the radiator on the outside back of the fridge.

I've labelled a few other connectors on the board...

D is the connection to the magnetic door sensor.
E is a connector to an RS232 connector under the front panel.
F is the connector to the display/buttons on the front panel.
G is a connector for external stuff, it's unused.
H is mains power out to the compressor outside the fridge.
J is Mains power in.
K is 240V out to the switching power supply that goes to the fan.

When I disconnect A, B and C, I get additional errors on the display, F1, F2 and F3, and replacing them one by one, the errors disappear. But always still left with the F6 error. Swapping around the sensor connectors didn't change anything.

The resistance on the sensors are:

A 6.89 k Ohm
B 6.88 k Ohm
C 7.15 k Ohm

[redwire]

Re: Fridge - Gram

There seems to be other (but electronic) sensors? Pics shows 5 sensors for the "RF". I would look at the remaining two.
The three sensors have the same thermistor inside, but each has different cable lengths and thus part numbers. It is a 5kΩ@25°C NTC, B=3984 if Vishay NTCACAP.

Beyond this, the controller might have scrambled settings and need to be reset back to defaults.

[tmcw]

Re: Fridge - Gram

Thanks for the info and links, I hadn't found that document on the fridge. This document is fairly recent, our fridge is from about 2012, so an older revision, and one difference I can see is on the keypad, part 64, ours only has 7 buttons, only 3 numbered buttons (1, 2 and 3, plus the other 4 buttons, +/-/P/Q), whereas the newer revision has 5 numbered buttons (1, 2, 3, 4 and 5, plus the other 4 buttons)

The cable to the outside temp sensor (C) is a fair bit longer than the other 2, so that might account for the higher resistance?

Now, part 68 (Electronic LTP), a small board, I assume this is a "low temperature protection board, but I can't see it in the lid, and all the wires off the mainboard are accounted for (I think). Perhaps it's a daughterboard connected directly to the mainboard, so underneath the mainboard (I didn't take the mainboard out on either fridge yet).

Now, according to that document, it looks like a standard part on all 3 versions (RR, RR* and RF), but maybe it wasn't on an older revision like ours. Or was incorporated on the mainboard in older revisions. The RR is a regular version (like ours), RR* has a glass door with LED lighting, and the RF is a freezer.

Since it's a "Bio" fridge, frost free/frost protection is very important, as the fridges are used to store cultures/bacteria, and frost can damage the cells, generally when we get fridges, they have to be frost free. So I assume this fridge *should* have frost protection. I did find a setting in service mode that pointed towards it being for activating and deactivating frost protection, but it didn't seem happy when the setting was deactivated (constant alarms); I need to look at that again, and see if I can dig out the proper service manual for that, as the one I did find was for the 5 numbered buttons version (newer revision).

But to your last point, maybe the settings have been garbled, an associated maintenance company did look at the fridge when it was flagged as faulty, and they may have messed with settings. I'm away from the fridge until Monday, but will check and compare settings between this one and another one that is not giving the F6 error.

EDIT: This is the link to the service menu items, but for the 5 numbered buttoned (later?) revision. I'll have a look for a service manual for the 3 numbered button version.

https://cdn.badcaps-static.com/pdfs/...dad6d6c7bc.pdf

[redwire]

Re: Fridge - Gram

Some Gram refrigerator control boards can be programmed for the different options and I thought this board might be (wrongly) set for the model having the electronic LTP board option, so it is looking for something not there in your model.
The LTP board might be a dedicated board with ability to override the main controller, in case it gets stuck on. Some safety functions are done that way.

The pushbutton on the control board I would definitely try... push and hold see if it goes into TsT mode.
If another tech was in there, double check all connectors as well, they do leave a (new) mess sometimes.

[tmcw]

Re: Fridge - Gram

Cheers for the input, it's much appreciated.

Digging deeper into it, I found some wiring documents for other Gram fridges/freezers, and can see some of the other connectors, particularly the ones on the power-in side of the board are used for fans on the condenser, or heating elements for defrost functions on some freezers, for example this document:

https://cdn.badcaps-static.com/pdfs/...9133678e01.pdf

And this document shows the wiring with the LTP board wired in:

https://cdn.badcaps-static.com/pdfs/...06b48b30aa.pdf

Now, unless that LTP board is down near the compressor at the back of the machine, I don't know, but that wiring seems to suggest that there is a connection between the LTP board and the display ribbon cable, and I'm pretty sure that it doesn't have that. You can see the F-sensor connected to that board there too. And these and other documents also include the E-sensor, which isn't used on our board (top-right connector in the mainboard photo), which I gather is an extra sensor that can be moved about the fridge chamber, either in the air, or in a container of liquid, to check on the distribution of coldness throughout the fridge.

Also, the parts list in the document you attached earlier does show the LTP board as a separate board.

One thing I did notice is that in my photo of the mainboard, I had the door switch connector connected to connector 21, whereas it's connected to 20 in the wiring diagrams, so I'll need to rectify that, but I will at least check in the first fridge I opened up, that it is connected to 20, as I didn't remove any connectors in that one, just the wiring to the switching power supply, and check all the other connectors, make sure they are all in the same place. It didn't seem to affect operation though, the chiller/compressor came on as normal, perhaps the extra connector there is for a fridge with 2 doors?

I did try the pushbutton (couldn't resist!), but all it does is switch power off completely to the board, and when you release it, power is restored.

Knowing what I know so far, I'm beginning to think our fridges don't have this LTP board, and that the settings got corrupted, or changed, so when I get back to it on Monday, I'll go to a working fridge, write down all the settings through them menus, and compare with the settings on the fridge with the F6 error.