No trim pot on my PSU ? - advice needed

[antenne]

Hello all

I wanted to calibrate my power supply, as i've been having problems w my internal harddisk
failing to boot periodically.
But i cannot find the trimpot on my PSU..

The only place where i guess it should be, there are 2 resistors wired together

pic here

https://www.facebook.com/photo.php?fbid=10150831874509182&set=a.10150216155409182.341367.824194181&type=1&theater

https://www.facebook.com/photo.php?fbid=10150831872764182&set=a.10150216155409182.341367.824194181&type=1&theater


Can somebody verify that that is where the trimpot is supposed to be ?
- And if so, can someone with a service manual please lookup what the specs for the trimpot is
so i can put it in ?

Thank you in advance for any help and advice !

best wishes, - Kim

[antenne]

I found a pic of the E III psu

http://eiiiforum.com/picsfromusers/eiiicf/

and it cornfirms my guess: - i have a psu without trimpot 

Can somebody help with info on the type of trimpot it needs ?

TIA - Kim

[esynthesist]

Hi, the PSU information is not available in the EIII Service Manual.
So I have to open my EIII and have a look on the printed information on that trim pot.
I'll try to do that in one of the next days...

[antenne]

Thank you !! 

[dvdborn]

I just had a look at my broken PSU and it doesn't have any markings on the trimpot.

When I measured it, still connected to the main board of the PSU, it gave a value of 2,06 ohm with the meter setting at 20k.

[esynthesist]

Well, mine has some labels but unfortunately the most important one - the ohm range - is impossible to read because a transistor and cooling iron are hiding it.
I tried to do a search on the internet based on the brand and product code (which are readable) but that didn't give any reliable result. The trimpot on my PSU is from Piher Spain, and the code is 735.

Measuring the ohm value when installed on the PSU board is not reliable, because the measurement also takes into account other resistors in the circuit.

Maybe I'll remove the cooling iron tomorrow (but this means also releasing two transistor cooling screws), in order to be able to read the ohm range.
Or I will desolder it.
But to be honest, I don't like touching it, because it works fine right now...
So I can't promise I will actually do it.

[esynthesist]

I was able to read the information on the trimpot by using a tiny mirror sheet
It's a 2KOhm trimpot (from Piher Spain, code 735).
I hope this helps.

[antenne]

Thank you - it does help.

i'll try and install a trimpot w the same specs - that should do the trick i hope.

Thanks again - i'll let the list know the outcome.

Kim

[antenne]

I installed a 2Kohm trimpot - and it worked perfectly

Now i can trim my psu to 5 volts -

Kim

[jazzyjoepass]

The problem with trim pots is that they drift with age and vibration.
Probably the previous owner who put the two resistors was trying to fix the value and overcome those issues.
Was the reading at 5.05V with the fixed resistance?

A better alternative would be using compact flash memory as an internal hard drive. It should draw lesser current and put a lesser load on the power supply.
From what I see on the posts on this board, the EIII has stability problems primarily due to power supply issues.
If we could all put lesser load on the PSU, the EIII might be more stable.

I also suspect some drives don't work partly because it draws larger current than what the PSU can support.

[antenne]

The problem with trim pots is that they drift with age and vibration.
Probably the previous owner who put the two resistors was trying to fix the value and overcome those issues.
Was the reading at 5.05V with the fixed resistance?


A better alternative would be using compact flash memory as an internal hard drive. It should draw lesser current and put a lesser load on the power supply.

no the reason i wanted to install a trimpot was because it was too low..

 thanks for your post on the CF AztecMonster - i just emailed japan re purchasing one


all the best, - Kim