FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 

DRS78 repair (was help with german translation) - thanks!!!
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2  Next [all]
Author DRS78 repair (was help with german translation) - thanks!!!
Paradigm X

I have just picked up a drs78 but the PSU is a little poorly. I found a service manual but its in German.

Could anyone who speaks German help me out with the attached bom, and notes? I think i can work out most of the caps and voltage regs, but a second opinion would be very helpful.

On a related note, ive heard that replacing voltage regulators is a good idea?

I was planning on doing the caps anyway.

A full service manual is here if anyone is interested; anual.pdf

Many thanks, Ben
I have two dead DRS78 d'oh! The service manual seems to be very helpful, but had no luck so far...

Let's see about that blurb:

Taking out the PSU-PCB:

1. Take out the plugs
2. Unscrew the voltage regulators J001 / J002
3. Desolder the connections (facing the back of the unit)
4. Unscrew four screws on the right side of the unit
5. Take out the PCB
6. To put it in again, make sure you don't forget the mica washer (?) and insulating disks on voltage regulators J001 and J002

Hope this helps. Can you decipher the parts list?

Paradigm X

Many thanks,

It kind of works but has a very noisy input. At least one PSU cap is physically cracked, so the PSU definitely needs fixing.

The only things im not sure about on the PSU list are

G050 G0511 G052 - Gleichrichter? Bridge Rectifier maybe?

HLZ Kuhlkorper

Netztrafo (transformer?)

Many thanks. Kind regards
Paradigm X wrote:
G050 G0511 G052 - Gleichrichter? Bridge Rectifier maybe?

HLZ Kuhlkorper

Netztrafo (transformer?)

Rectifier; heat sink; power transformer.

No idea though what HLZ stands for.
No idea about HLZ either... hmmm.....
HLZ, hmm...


Mr. Green

but seriously, Dynacord are very friendly and helpful. they sent me a knob for my DRP-20 and a PDF of the VRS-23 service manual for free. if you get stuck, try contacting them - maybe they even have an english version of that manual...
roglok wrote:
HLZ, hmm...




Paradigm X
Cool thanks all.

Ill desolder the PSU pcb tonight and see whats up.

Ill also contact dynacord, need the serial number to do so.

cheers, thanks for all your help (might not be over yet !)



Paradigm X
Hi all

Well, thanks to your help, i got the psu pcb out and had a look.

The caps were shot, all cracked. I desoldered the lot and replaced with nice new panasonic ones, double the capacitance. I had to replace the huge 4700uF one with 2x 3300uF ones.

Im not sure if the big rectifier is broken, theres some brown marks on the underside?

Didnt get a chance to put it back together tho, so wont know until the weekend if its helped Dead Banana

Cheers all, ben
wow, those shattered caps were mounted quite close to the power regulators. maybe the heat has cracked them... good luck with the restoration!
Seeing the pics I get an idea what HLZ might refer to. HL should refer to Halbleiter (= semiconductor) i.e. the rectifier. For some reason the Z most likely denotes that the HLZ is a heat sink to be mounted directly to the rectifier.
Paradigm X
Thanks. I was looking around for anything marked HLZ, but didnt find anything.

mine also appears to be missing the two 1n4002 diodes shown on the schematic. Not sure if any issue.

Still not sure whether to replace the regulators, or anything else, while its open.

Im going to replace the hard soldered connectors with some connectors, so i can pull it in and out easier.

Might even replace that rectifier, the burn marks look suspicious.

Sadly, theres about another 7-8 pcbs, all full of electros and tantalums Dead Banana I really ought to do them at some point too.

I dont knwo if anyone is interested, if i carry on ? Ive got more photos too if anyone is interested.
The discoloration under the large bridge rectifier looks like heat damage. It doesn't mean the bridge is bad, but it is a sign that it was pushed pretty hard. It wouldn't hurt to replace it, but be sure the replacement is capable of at least the same amount of voltage and current. If you have a scope you might be able to see if the bridge is working OK by looking at the +output of it when turned on and seeing if you see both "humps" of a full wave rectified signal. (twice the rate of your AC voltage input)

It's possible that your board is an earlier version than shown in the service manual, before they added those two protection diodes. Chances are they were added because earlier boards got damaged without them. You could always solder them onto the bottom of the board.

Damage in a power supply is sometimes a symptom of a problem elsewhere in a device. You should be careful when powering it all back up to make sure the output voltages are right and the regulators aren't overheating. Those would be signs of problems elsewhere.

The regulators themselves have short circuit and thermal protection, but when shorted they could draw a lot of power from the unregulated part of the power supply.
Paradigm X
Many thanks Dave, as always a very clear and helpful reply.

If i may ask one more question please?

Do the voltage regs need replacing/deteriote/compare badly to modern ones? They are prob around 30+ years old.

Thanks, ben
If they function, the regulators are probably fine. They can deteriorate somewhat over time because of excessive heat, but at the current levels shown in the schematic, and with a decent heat sink, that probably wouldn't happen here.
Paradigm X

I finally got some time (and round my fear of 240vac!), and wired up the psu with shielded plugs, and it works really well!

Still a tiny bit of noise, to be expected from a unit this age, but fundamentally working as it should!

Thanks so much everyone for your help.

There are still about 5 pcbs to recap, which ill do as and wehn. But now its completely usable!

thumbs up It's peanut butter jelly time!
Hello, I have a fully functional DRS 78, I love it, I can tell you your work is going to be rewarded This is fun!

Also works without much noise, but is easily overdriven. I keep it near my VRS23 (sorry, I just love to talk about this units!!)

I have a broken down DRS 78 too, I have not gotten around to fix it, but there´s this helpful looking
yahoo group

The reverb on the DRS sounds like falling into the abyss, it´s all DARKNESS woah
Paradigm X
Yes, i really took to the sound of the dynacord stuff

The VRS23 is my favourite so far.

The DRS has, not quite a noise, but a low level, high pitched whine in the background. Im going to go thru all the other pcbs and change out all the electrolytics and tantalums.

Ive also just picked up 2x Tam21s and an SRS56, all needing some repair, for a steal! at least theyre (relatively) easy to work on.

Nice one.

[edited for clarity]
Paradigm X
Ok, well i had a good play with it this weekend, sounds great, still a bit of nosie to deal with.

But a concern (?) is that is got quite warm... the psu uses the side of the case as a heatsink, and it got hot, not too hot to touch, but noticeably warm... how hot is too hot?

I didnt add the two diodes, its a pain in the aris to take it apart.

So im going to carry on replacing all the electrolytics and tantalums on the other pcbs, which shoudl at least, hopefully, improve the noise levels further. Its such a nice sounding box, all the dynacord stuff of that era is lovely.

cheers, Ben
just got the Dynacord DRS-78, although it's cosmetically mint, it doesn't work. It all lights up, and what i've noticed is that the input level meter is red to 0db even though nothing is plugging in the unit.

I hear it's relatively easy to maintain such unit. Would changing the caps on the PSU fix this? Any suggestions what to do first?

many thanks,
Dear all,
Just bought a recap drs-78, fully working a little noisy but correct.
Does yours get super warm? I should say hot, I don't feel confident to let it on the all day... What's your experiences?
Thanks a lot for the feedback
its standard the casing is the heat sink touch it around the case you will notice its cooler on the further sides it means its doing its job properly the ensoniq asr10 is the same .
Thanks for the answer,
So no need to freak out until smoke!! Ha ha
Have a good day folks
Reviving an old thread here...
I just want to chip in, that I just got a VRS-78 with a lot of hum/noise. I changed the four capacitors close to the 15v regulators (they all looked a little cracked), and everything works like a charm now. w00t
I changed the two 470uF for 1000uF ones, since that was all I had - that shouldn't be a problem, right?
flo wrote:
I have two dead DRS78 d'oh! The service manual seems to be very helpful, but had no luck so far...

Do you still have them ?
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2  Next [all]
Page 1 of 2
Powered by phpBB © phpBB Group