Aiwa HT-DV90 Help (no power)

[1976saint]

After the successful help/diagnosis and repair of my old AKAI AA-RL1 AMP (https://www.vintage-radio.net/forum/...d.php?t=154464) my next project is to get my old Awia HT-DV90 working again. I'd like to use it again as a CD-Player to go with my newly working AMP.

It had a problem firstly that it didn't read disks anymore but that was fine as I primarily used it for TV surround due in most part to it's dual OPTICAL Inputs!

Then one day it wouldn't power on. I put it in storage and a few years back but recently took the lid off and found that the FUSE F604 had blown.

So not being good at electronic circuit diagnostics (but handy with a soldering iron) I turn to you guys to once again help point me in the right direction as to where to start looking please.

I've attached the service manual (which I found free this time) and photos of the power PCB. Note the underside which look to be some kind of capacitor maybe which do not look great.

https://www.manualslib.com/download/...a-Ht-Dv90.html

Kind Regards
Paul

[Silvered_Mica]

Well if it's banging fuses start with the filter block and look for shorts or leakages, that’s the bit between the mains input CN61 and the rectifiers BD62-BD63.
Check the rectifiers as a diode might have gone short. Check the chopper FET Q234 for shorts leakage.
It's also possible that one of the controller IC's has failed IC57-IC66.
Check D662 and Q617 if these are having problems they could have destroyed IC66.

These are the first few checks I would do. Good luck

[Silvered_Mica]

Another thing I should have mentioned, if it's a glass fuse and it has gone all black your going to have to do some fault finding
but if the fuse has a small break in the wire you might be very lucky and just be able to change the fuse.

[paulsherwin]

If nothing has obviously gone bang or cooked then I would certainly try another fuse. They do degrade with time and eventually fail during the switchon surge.

If the new fuse blows immediately then you do indeed have a more significant fault, and the player is likely to be BER. It does look as if something has got very hot under the PCB, but the photo may be misleading.

[1976saint]

Thank you for the advice, I'll take look at the parts advised. The fuse was black (gone bang) unfortunately!

[Diabolical Artificer]

Are those two jumper wires on the underneath of the PCB factory or a bodge? Check them against the schematic.

What are the voltages the PSU supplies? It may be possible to find another SMPSU that will fit to save fixing this one, although of coarse the rest of the device will need checking for shorts before powering up with a new PSU.

Andy.

[1976saint]

The two jumper wires underneath look to be a couple of components covered with a plastic sleeve. They have a bit of resistance when I put a meter over them. They are not on my schematic, the version of the HT-DV90 is the K variant possibly which could stand for UK (and would make sense)?

I guess there could be another SM around showing them but I've not come across any as yet.

Searching the web for this unit is also proving pretty elusive atm.

@paul , I think I might have tried a new fuse when I first looked at the problem but I can't remember as it was about a year or so ago. The blacken part of the board your referring to is melted black sleeve (but cover two unidentified components) it looks like and around the base of the big capacitor solder point. I'll take another pic for a better look-see.

Paul.

[1976saint]

Photos of jumper bodge components, and burn marks attached.

[paulsherwin]

It could be that that is a factory modification made during the production run after some problem was identified. It's not uncommon to find components soldered onto the wrong side of a PCB. The work doesn't look very professional though.

I've no idea what the components are or whether they've overheated, but the third pic doesn't look good with what appears to be melted solder.

[ekjdm14]

I'd agree it does look like things have got a bit hot there. I wonder if they were (underspecced) resistors that have been getting hot and going progressively lower in value/passing more current/getting hotter until they've reached a runaway situation and popped the fuse.

If the apparent heatshrink(?) could be removed and they are in fact resistors, and still readable, then I might lift them out of circuit and check their values.

The only other thing they look like to my mind, is small inductors that I've seen in a package similar where the bodies look to be covered in tubing like that. Doesn't look healthy though.

[ben]

Looks like there's some glue there attaching those track side resistors which has turned conductive. Remove it all before attempting to power that up again.

[Silvered_Mica]

Hello,
When looking at the pictures posted I first thought they had put some avalanche protection diodes across the output
of the rectifiers but after enlarging the picture and putting my glasses on I can now see that they have paralleled the
outputs of the rectifiers, possibly via two low value resistors? I have not seen this done before, I imagine it's maybe
done to share the current as one rectifier is rated at 1 amp and the other is rated at 4 amps so maybe the one rectifier
was a bit borderline. Or maybe they need to share the reservoir capacitance, it's not clear
I don't see why it needs two rectifiers anyway, it obviously didn't work very well if they had to strap them together
after manufacture.

If that board burn between C653 and the link wire is a piece of track blown out then it's possible that IC67 has failed.

[1976saint]

The two parts under the board are I discovered at 330 (orange orange black orange brown) ohm resistor (the big foreground mess in picture ...track side3.jpg) and the other a diode.
Both seem functional in that the diode is correctly responds with a value one way but not the other and the resistor is also giving a reading but I'll need to desolder one end to properly check.

[Chris55000]

Hi!

Orange-Orange-Black-Orange-Brown is 330k ±1% tolerance - can you post close-up pictures of the components please - then I can issue a revised diagram sheet showing them & where they're connected please?

Chris Williams

[Chris55000]

Hi!

If you unsolder one end of each added component & remove the sleeving from each, I can identify what they are and complete my revision sheet, which I'll post for you, then I'll follow it up with fault-finding & repair advice for your unit!

Chris Williams

[ekjdm14]

Originally Posted by ben

Looks like there's some glue there attaching those track side resistors which has turned conductive. Remove it all before attempting to power that up again.

It's clear that it's likely to be "brown circuit glue" now you've said it! Yes that gunk goes crispy and conductive over time (I believe speeded by heat) and needs to be carefully got out of there paying attention to not lift/break any traces underneath it. I'd be surprised if it passed enough current on it's own to cause the symptom here but it is probably at least partly to blame for whatever failure has occurred. (Especially if it's been bridging across that 1% tolerance resistor).

[1976saint]

Uploaded images - should be attached, thank you.

[1976saint]

I found time to solderer those parts (attached). Both fail to supply a reading on my meter! So previously there was resistance from somewhere else?

[Silvered_Mica]

Could you give us the part number markings off the diode please?

[1976saint]

Hi numbes are IN4937 on the diode.