General PSU repair guides

edited August 9 in Chit chat
Not Speccy related. I'm just looking for a guide as such as to where to begin with a power supply repair. Realise this is a bit of an odd thing to ask however there are a lot of highly knowledgable people here, all I'm really asking is a pointer (or link or two perhaps) in the right direction. Although Google did point some resources out, its difficult to know where to start.

To my mind a PSU is simple (this is not the case here!) where you have a transformer, a bridge rect, a smoothing cap or two and something like a 7805/7812 etc regulator, aside from fuses that's me done with a PSU! :D

The unit in question is inside a freeview box, and I'm unable to find a wiring diagram. The unit is completely dead. I'm told (on the grapevine) they could overheat apparently, it was handed to me in its current state.

I'm quite aware of the dangers and precautions in dealing with mains electricity! Sadly I've only got a multimeter to do some basic tests with.

What I have done so far anyway , obviously powered down and caps discharged:

Continuity check to confirm L and N are present on the mainboard at the solder side and at their 'end of track' solder joint too (the board is split between high an d low voltages) , tested from mains plug pins to the track itself.
Could not find any fuses on the mainboard even a tiny 'diode' size one, unless its a can type.
Visually inspected all components and the board both sides for signs of burning, swollen components etc. I was hoping to find an exploded mains suppressor or suchlike, there are two such ones fitted similar to the ones inside the BBC Micro PSU actually.
There are four largish diodes that appear to be doing a passing imitation of a bridge rectifier, I've checked they only pass resistance one way. While I was at it, I also tested a few other diodes I spotted.
The small transformer, I've verified that the primary and secondary windings have resistance (ie: not open or short circuit)
Did about a dozen small continuity checks between various tracks on the HV side
Checked board visually for dry joints and general condition, appears visually OK.

Obviously all the above unpowered.

I'm a bit concerned test results may be skewed by testing components 'fitted' but don't want to be desoldering stuff just to test if I can avoid it!

The LV output has about a dozen or so wires in its plug apart from one red the rest are all yellow. I've not bothered to power it up to see if any voltages are present here, as I suspect its not getting that far. When I did power it up, it was silent although I'd of been alarmed if I heard any noises.



If it helps its a Goodmans branded GHD8015F2 which is based on a Vestel unit, although I'm not 100% sure which vestel type yet , this may provide a vague diagram however. This unit has a 3.5 HDD in it so its going to want a 12v supply as well as a 5v. I mention this as the smaller drives only want a 5v supply. The panel display is a vacuum fluorescent type similar to how VCR's sometimes had, I don't know if these type of displays needed any odd voltages like a -5vdc , an ac supply or something odd like a +19v etc etc

Pics later tonight if any thoughts please, as it was virtually free I figured it was worth a look at.
Post edited by spider on

Comments

  • edited August 9
    If it is the model I think it is (quick net check says yes)
    Then no complicated voltages from the p/supply just the usual suspects.

    I have 2 of these that have bit the bullet power supply and main board wise.

    The out put voltages from the p/supply as I recall is red wires 5v(for the chips,hard drive) yellow 12v(hard drive), black is ground /earth call it what you will.

    Personally I wouldn't bother with repairing as even when working they are a complete dog of a box operations wise and even after manually upgrading the firmware(which I think I still have)via the serial port with Goodmans official firmware they are still a pain.

    Not enough space here to list all the reasons why this box is so terrible( noisy especially vibrating case noise,random crashes,not recording programs,front panel display problems etc) but the most pertinent one is that the TV guide is stored in RAM and when these boxes were made the guide was relatively small, and there is not enough RAM to store today's much larger guide . This manifests itself in slow guide speed, missing items,non/missed recording of programs blah blah blah.

    Sorry to be a doom merchant but these boxes were rubbish at the time, definitely underpowered supply wise and seriously bad and frustrating in operation.
    Post edited by moggy on
    Thanked by 1spider
  • It sounds like you have a switch mode power supply unit there. Unfortunately these can be a pig to get working again.

    On the primary side, while being very careful, test that you have about 340V DC across the large high voltage electrolytic capacitor.

    Now with the outputs of the unit disconnected, test the +5V output. What voltage do you get? If you connect a test load (e.g. cheap USB load resistor or 6V / 12V vehicle lamp) does the voltage drop significantly?

    One very common problem is degradation of the “start up” electrolytic capacitor (on the primary side feeding the control/switching electronics) and the secondary / output side electrolytic capacitors.

    Mark
    Thanked by 1spider
  • edited August 9
    Forgot to add that when the p/supply failed I ran it for a while using an atx tower pc supply which provided a more adequate 5-12 volts, but did look rather clumsy but should be ok for testing purposes should you posses such a supply.
    Post edited by moggy on
    Thanked by 1spider
  • edited August 9
    Thanks both. It will be this evening before I can get at it anyway.

    @Moggy Thanks. :) from memory the points you make about ram etc are what I'd expected, I do have a later one (ex shop display apparently) the sata model with a 2.5 drive and about half the case size, that thankfully has an external 9v or 12v simple 'brick' PSU and its a near complete pile of you-know-what , that one loves to ignore schedules unless its reset fully (first time setup***) and also picks at random if it wants to turn an episode into a series record or not.

    *** I have discovered you don't lose all the previous data if you are quick in pulling the supply plug out about 3 seconds after forcing the first time init. That way only the settings are lost, most of the recording and scheudles that it chose to keep (lol) are still there. Then it usually behaves as you'd expect for about a month.


    The "output" plug has about 10 or so wires from memory. There's one red, the rest are all yellow. Possibly one or more may have a black stripe I'd have to check. If it was working I'd expect to find either 12 or 5 on the red line, a 0v line or maybe more than one, and possibly some other voltages, such as 3v or perhaps 12. I've not looked at the main logic board to see where it gets its 12v yellow line to the HDD from yet, it may have a dc-dc convertor on it or it may come from the main PSU board.

    I do have a suitable 12v/5v PSU I could use if needed. I'd rather not say erm 'insert power' into the HDD plug to try to "force feed" the rest of the board though!


    Main issue is lack of diagram I think. A pinout of the output plug would be most helpful.


    @1024MAK Thanks.:) Yes its a switch mode as far as I'm aware. I'm not really up on PSU tech as you can probably tell from my "basic psu" design. To be fair that has worked well in the dim/distant past for me! I'll perform some tests later this evening. I posted all I really tested the other day in my first post so far. I perhaps should of carefully probed the "low voltage" half of the power board to see if there was any sign of life (somehow I expect to find none) but when I was doing my initial examination it was no where near any power socket :)

    Safety is very high on my mind with high and/or mains voltages, especially where capacitors are concerned. Have done some TV work in the very dim/distant past (30 years ago nearly) so I try to think I'm reasonably safety conscious.

    EDIT... If I can convince my ancient camera to work I'll also take a pic or three of both sides of the board, I was not able to find said pics on Google but I'll admit I did not try too hard for that as its a maze.
    Post edited by spider on
  • edited August 9
    @spider

    Just did a further net search as I couldn't reconcile the p/supply wiring differences and it would appear that the picture of a freeview box listed as an GHD801F2 I looked at is actually a bloody 1621F2 so red face and apologies Spider.

    I will however see if I can track down some better info this time!! :))

    This to be going on with...

    Vestel T810 clone like the following...

    Digihome DTR0207 (Tesco)
    Digihome PVR80 and PVR160 (Argos)
    Dual DPVR80 and DPVR160 (Asda)
    Durabrand DPVR801 (Asda)
    Evesham PVR160
    Goodmans GHD8015F2
    Grundig GUSTB80IV and GUSTB160IV
    Hitachi HDR080 and HDR160 (Argos)
    Linsar LPVR160
    Maplin PVR80
    Proline PDFV70
    Sharp TU-160H
    Techwood PVR80 and PVR160 (Tesco)

    A discussion here casts doubt on whether it will receive signals properly though it's above my head to be honest.

    https://www.radioandtelly.co.uk/cgi-bin/forum/YaBB.pl?num=1227676643

    A bit more of a search leads me to believe this is the power supply part number Hitatchi 16pw36-2

    The schematic can be found here..

    https://elektrotanya.com/hitachi_16pw36-2_power_supply.pdf/download.html#dl
    Post edited by moggy on
  • Thanks.

    I did attempt to take some pics but the camera had other ideas unfortunately.

    However: Upon an even closer inspection in bright daylight there are two side-by-side 1000uF 16v radial electrolytic capacitors, and one has a very slight (not really sure how to describe it) bulge in the top, almost as though the folded aluminium was trying to open from inside. So I will for the sake of it just replace that and its next door neighbour as they are both the same rating. I doubt that would fix it somehow and that may be secondary damage perhaps, but you never know.

    Downside is I know I have some somewhere but I can only find 16v 100uF's and they are axial but have long leads :( I'm not sure if its worth replacing it with one of those "just to test it for a few seconds" or not. Realise if the replacements were the same capacitance but higher voltage (not lower) I'd be good but hmm. To my mind its 1/10th of the factory unit but it is a capacitor. My mind also says "try it but don't think about leaving it on until you get your hands on the right ones"
  • I have edited my last post in case you missed it, with some more information.
    Thanked by 1spider
  • moggy wrote: »
    I have edited my last post in case you missed it, with some more information.

    Thanks. :) I had , as I'd read your post before you added the second useful link.
  • edited August 10
    Not having had chance -sigh- to look or do anything with the box of tricks yet, I did manage to do a little research and came up with this eventually which shows the board in detail. It does point to a fuse too that I'd missed (assuming I have it on mine) , the PVR80 :

    http://www.vwlowen.co.uk/vestel/digihome.htm

    Some good pics there.

    I can't compare the pic to the unit directly yet however it is virtually if not completely identical. The only difference really I noted is not important and is the fact the HD is set to CableSelect on mine and has the HPA disabled.

    I think my first port of call should be to examine that fuse for continuity and then obtain and fit a replacement cap (might as well change its neighbour too, same value for the sake of a £1 or less) , annoyed I can't find the ones I have here only the 100's not the 1000's uF's hmms.
    Post edited by spider on
  • Can't edit above (time expired) but this thread:

    https://forums.digitalspy.com/discussion/1309563/pvr80-died

    Contains a lot of helpful info for me it seems. Merely posting in case it is useful to anyone else here, you never know! :)
  • For various reasons beyond my sane control I've not been able to do anything with this just yet (sorry)

    However aside from one obvious 'slighty erupted' cap (I'll change all three as they are going to be pence for some 1000uF radials) further reading and digging also showed a diode on the main board that was short circuit. :D , figured that could not really be good news.

    The interesting thing about that was its across one of the 5vDC feeds, I was not sure I was mis-reading it "in circuit", despite it being a surface mount one I removed it and metered it to find that there was almost no resistance either way! , elsewhere says its for protection, board "should" boot up without it but unwise to leave out, I'll get a suitable replacement while I'm at it, zener or something I guess to tag on.

    As a sidenote I do see various "repair kits" for a few types of these boards, this one is a Hitachi 16PW36-2 although elsewhere it shows suitable substitutes too. The repair kits although reasonably comprehensive(ish) seem a bit too pricey for half a dozen components, with the possible exception of a small 4pin IC of some kind.
  • ‘repair kits’ often are more expensive compared to buying the parts individually yourself. Also they may contain parts you may not need (so called ‘universal repair kits’).

    You are of course paying someone else to buy the components (including the cost of P&P), sort them out, then repackage them. Sell them to you, and then post them out... Plus a bit extra for their profit...

    Mark
    Thanked by 1spider
  • Yes I agree, hence me saying "a bit too pricey" , although I can see the value (no pun) for some who just want a "fix it kit" without having to search out components. Good point about said kits likely having unused items within too. Plus there's always the fact that you may still need another cap / diode that's not part of the kit, its not like they are a complete component set.

    I'd probably only get a "kit" if it contained an item or two that was either difficult and/or expensive to find elsewhere. Having said that in the past I've purchased retroclinic's (Mark.H's) PSU repair kits for B's , iirc it was a pack of five I had a few years ago, I think I've still got one unused "set", but they were sanely priced.
Sign In or Register to comment.