Jump to content

Recommended Posts

Posted

Hi there. I have done a few repairs but this is my first strip down of a Hafler DH200. Looking for some advice on where to start eg what electrolytics to replace. I think there is a lot already covered on this topic - so maybe pointing me to the best thread would be a good start. Thanks 

Posted

Here is my project… not sure how this got so rusted - have you ever seen a case this bad??

Apparently the amp works but concerned the inside took a hit as well.

i have some work ahead but am committed to bringing this back to life!

IMG_0754.jpeg

AEE74BEC-16E3-4B03-8CC0-EAF7C6086A49.jpeg

Posted
On 28/12/2024 at 10:41 AM, ganache said:

Welcome to the forum Grant!  You might check this out first 👍

 

A great referral for @GrantB to check out!

Mark at Sonic Art really knows what he is doing, and his restoration provides Grant with a great blueprint for his restoration project.

  • Like 1

Posted

Thanks for the link to Mark at Sonic Ark’s thread. This is the best single resource I have seen on a DH200 rehab, and what actually prompted me joining this great group (happy I did).

So onto the project… after a visual inspection I started putting a Game Plan together (it may have been worth running some tests first, all I know is that this worked when I purchased it):

- strip out everything

- sand down and repaint chassis and cover (inside and out due to extent of rust)

- replace all external hardware (due to corrosion): Fuse holders, input sockets, speaker terminals, switch, rubber feet

- look for silk screen or face label

- replace electrolytics and a few film and disc caps (C1, C5, C7-8, C10, C12, C14-15) 

- test and salvage line caps if possible 

- replace diode bridge

- order and be prepared to replace: R1-R7, R9-21, R38 (signs of overheating - will have to look into that)

- as above for: Q1-7

- replace some of the wiring

- maybe replace the line cord

- if I decide to keep this unit: look into adding speaker protection and soft start-up module 

- load up on luck and patience 


And let the games begin !!

 

 

  • Like 2
Posted

Here are some photos of the strip down…. I took a lot for my records.

Fairly straight forward other than the indicator light removal (struggled to get the holding clip off- eventually used a long nose pliers to bend open the tabs), also ended up cutting the line cord to break out the grommet, I cut a few of the solder tabs off the fuses as the solder was so heavy and hard to melt down

 

step 1 down.IMG_0818.thumb.jpeg.1ae48981b66259c71c42c7b72177ac80.jpegIMG_0766.thumb.jpeg.f16e79664a33e4ac9eaf55301b39f3e9.jpegIMG_0819.thumb.jpeg.7fd7cb291f2e4e37073cec0d33c0a740.jpeg

  • Like 1
Posted

painting underway… stripped with orbital sander 120, 220 then 4 light coats (possibly too light), then hand sanded with 600 dry (very lightly, just a few passes).

ready for the last couple of coats…

—//—

 

Here are some photos of the strip down…. I took a lot for my records.

Fairly straight forward other than the indicator light removal (struggled to get the holding clip off- eventually used a long nose pliers to bend open the tabs), also ended up cutting the line cord to break out the grommet, I cut a few of the solder tabs off the fuses as the solder was so heavy and hard to melt down

 

step 1 down.IMG_0818.thumb.jpeg.1ae48981b66259c71c42c7b72177ac80.jpegIMG_0766.thumb.jpeg.f16e79664a33e4ac9eaf55301b39f3e9.jpegIMG_0819.thumb.jpeg.7fd7cb291f2e4e37073cec0d33c0a740.jpeg

  • Like 1
Posted

Got my parts order in. Took a few hours - I have to get quicker next time. Where did got stuck:

- C1 coupling cap (blocks DC on input)- I struggled to decide between film and electrolytic. Went with the film 4.7mfd based on research. 
- film caps - I was not sure if the voltage in the parts list referred to DC or AC. Friend advised it is the DC voltage.

- decided not to replace line filter or Mica caps for now, too pricey

- bridge rectifier- GBPC or KGPC .. I believe the difference is the extent of the heat sink and depends on manufacturer. Got the full heat sink casing.

- resistors - went for metal film over carbon

- got the 2N5551 transistors to replace 2N5550

 

order is done! Will strip down heat sinks next and might put in dishwasher (when missus is not looking). And clean boards with rubbing alcohol .

 

  • Like 1

Posted

Sorry I'm so late in suggesting this, but it would be better, I think, if you could find the time to create a thread over in the "DIY Audio Projects" section titled "My Hafler DH200 Project" or something similar, and repost all the photos and commentary from here to there. Probably get a much larger (and appreciative) audience if you do, and lots more comments and maybe advice along with it. Bit of a hassle, but probably worth the effort.

PS you could also ask the admin. people if they could simply move the whole thing for you. Go to your first post, click on the three dots in the top right corner, choose Report, and suggest the move.

PPS you could also tell me to piss off, and ignore me. I get that a lot.

  • Like 1
  • Thanks 1
Posted
2 hours ago, The Rock Puppy said:

Sorry I'm so late in suggesting this, but it would be better, I think, if you could find the time to create a thread over in the "DIY Audio Projects" section titled "My Hafler DH200 Project" or something similar, and repost all the photos and commentary from here to there. Probably get a much larger (and appreciative) audience if you do, and lots more comments and maybe advice along with it. Bit of a hassle, but probably worth the effort.

PS you could also ask the admin. people if they could simply move the whole thing for you. Go to your first post, click on the three dots in the top right corner, choose Report, and suggest the move.

PPS you could also tell me to piss off, and ignore me. I get that a lot.

Thumbs up - the suggestion re moving everything over to "DIY Audio Projects" that is, not the PPS suggestion.

This already looks like being a great restoration, which deserves a good audience.

  • Like 2
Posted

Painting is complete, after about 7 coats. Next time I will use a primer and satin auto trim, but nevertheless I am happy how it came out with the matte. 
After getting some advice, i decided against cleaning the heat sinks in the dishwasher. Brushed them down with a vinegar based surface cleaner and windex. Then applied a light coating of matte black rust paint. I was assured that a light coat would not significantly reduce heat transfer. 
 

here are the results:

IMG_0917.thumb.jpeg.0de4a9c54decc508fdd6c6460bcca6c3.jpegIMG_0918.thumb.jpeg.bff4544cfa414279b091a05acfe6e0d6.jpeg

  • Like 2
Posted

Here are the heat sinks:

image.thumb.jpg.4970680f221d119f095f954ccd018640.jpg

 

and the parts have arrived, took only one day to deliver. I got some extra for bulk and shipping discounts. No excuse to work on more Haflers … but let’s not get ahead of ourselves just yet.

 

IMG_0932.thumb.jpeg.c89ecbf8b9668475808899e95ca9e9d2.jpeg

 

  • Like 3
Posted

Ok so most of the PCB work is completed, for now anyway until I test. All electrolytics replaced as well as a couple of film caps and R38. In the process I found a couple of very dry joints almost non-existent and one speaker fuse was 15A as opposed to 2-3A.

i decided to re-wire with 18g shielded twisted pair (next time I will use 22g), I also need to ream out the speaker terminal holes as they are just too small for the new universal terminals….

 

IMG_0934.thumb.jpeg.62753029cfdfd1ef4edaa839a4f826b4.jpegIMG_0936.thumb.jpeg.64d3f4ceed8456cebcad66a27d117ee0.jpegIMG_0937.thumb.jpeg.7bf79bcf81a4cf3e1d187cdea45e5f5a.jpeg

 

  • Like 1

Posted

The signal hook-up wiring is almost complete, next time I might put some heat shrink on the joints - but without it is easy to see a bad joint and test. Speaker post holes were easy to ream. Some cold testing coming up next, will add the following resistors to the test list as I believe these are critical negative feedback resistors: R22-25, and test P1

several removed caps tested off spec, a couple as bad as 50% off … good that I replaced them.

for the audio inputs: I have connected the ground on the left input directly to the tab of the terminal which should bond ok to chassis with the insulator ring removed

for the right channel, I will likely add the insulator so that R1 sits between the signal and chassis ground - and use a lug with one screw to the chassis.

now that I look at the diagram I see R45 for the left input - this was omitted in my build (I will review this). I am not sure why a different configuration is used for each channel. 8F3E228D-10C6-45B1-8A01-DDE7F3CDE592.thumb.jpeg.31d9d9f3ad42b664906c7127635cf88b.jpeg

 

progress so far:

 

IMG_0952.thumb.jpeg.787432c856d1484881aa81de84541c95.jpegimage.thumb.jpg.31670b6c8528cda8aa3c76216c192a16.jpg

 

  • Like 1
Posted

Ok I have started to reassemble into the case. I replaced the power cord but maintained the two conductor input without ground. I am re-wiring the daisy chain ground into star - and might add a busbar across the main caps.

I replaced the 2.2 Ohm R45, and kept it on one input only as per the schematics. I will isolate the inputs from the chassis and then run the ground leads to the star centre ground. The cable shield is grounded at one end only, onto the input terminal and ground lead mentioned above.

IMG_1042.thumb.jpeg.af4e76daf7810a22999fe8db7a98b27e.jpeg
I replaced the switch and new companion cap. I used spade terminals for ease of future replacement.

IMG_1048.thumb.jpeg.d068e3d3d449867384bb3eb501f7ab96.jpeg

I will add a current limiter on the switched line in - which I have incidentally connected the hot wire in from the mains cable.

I replaced the bridge rectifier with 35A and installed a new ceramic cap across it - note the small size compared to the disc cap. I believe this is fine as the specs match.

IMG_0998.thumb.jpeg.48311c9a5b41b8985ee61600e2e2bdbf.jpeg

IMG_1047.thumb.jpeg.afb38d4c42c9f8c1882147ccc533fecd.jpeg

  • Like 2
Posted

I decided to furnish a busbar - looks much better! I added a chassis ground behind the rectifier, isolated the RCA inputs from the chassis and then ran ground wires from the input terminals to the new centre point chassis ground (keeping a 2.2 Ohm resistor on one leg), and  from there to the busbar centre tap. 
This completes the conversion of the daisy chain to star ground. 

 

IMG_1083.thumb.jpeg.3defa1c6cc29373c82572e1cc63bca87.jpeg
IMG_1082.thumb.jpeg.fadf1d2d5f3412e95702490493d8daa3.jpeg

 

Heat sinks are back on. I left the grounding to run through the heat sinks onto the chassis via the set screws. Adding a wire ground may be a better option in the future. 

I popped the lid on … wow what an improvement to that old rust bucket!!

 

IMG_1094.thumb.jpeg.229539b216cb8d465fc84761d39f70b9.jpegIMG_1093.thumb.jpeg.73d15eac7242c20d4110c6d35f989c86.jpegIMG_0762.thumb.jpeg.dc0da3da8461d83c996ac36be9cc2a45.jpeg

 

Preparing for power up next…

  • Like 2
Posted

Did you look to 'float' the central power supply Zero volt (between the caps) from chassis earth?

Posted

No, I did what most people have done and went from the centre tap between the caps directly to the chassis. Would you recommend something different? 

Posted

Man what a rusty old Halfer! Good thing is they are quite simple to strip down as you have shown, looks good now, funny it must be a late DH200 as those heatsinks with the curved edges are usually found on DH220's.

 

The earth/zero volt between the caps should be floating, the transformer earth connects to the centre of the bar, and the speaker neg posts connect up to the same spot. Use the factory manual photos for reference, your power supply should stay as they designed.

 

For the RCA inputs I would suggest running a wire from each earth tag to the star earth tag you have added in the centre of the chassis, add a resistor, 8-10 ohms to the tag, connect both L&R earth wires to the resistor. Also make sure your input wiring goes straight up from the RCA, then bends to the left/right, then bends forward to the board where it attaches, keep it away from all the power wiring, and sitting close to the case when the lid is on.

 

When you power it up its good to have 4 multimeters, 2 for bias and 2 for dc offset, or work on one channel at a time if you dont have enough meters, pull the fuses from the other.

 

Q1/Q2 and Q5/Q6 need to be matched in a DH200 as it has no DC adjustment circuit, its not hard to simply do Q1-6 all matched when replacing them, if you dont have one get a cheap transistor tester off eBay, they work very well. It will be interesting to see what your dc is when you first power it up.

There are a lot of parts that need checking for tolerance in the input driver stage, resistors to check:

R6,R7,R17,R19 are 2.2k, need to be spot on.

R9,10,15,16 are 22 ohms, also need to be spot on.

R12,14 are current flow resistors for the differential pairs, these are 560 ohms and need to be good, quality metal films should be used.

R11,13 are 39k.

R4,5,20,21 are 100 ohms, also need to be matched.

 

  • Like 1
Posted

Also your input caps,  what are they? My suggestion would be for budget with great performance,  some Dayton 4.7uf 1% polypropylene,  with Dayton 0.1uf film and foil bypass across them. For a few more bucks Mundorf poly caps sound very decent in the hafler  input.

Posted

Hi SonicArt, so happy you dropped in - you feel like a bit of a legend to me as your previous post were next level and inspiration to me.

I will return the power earth to float separately from the chassis ground (I always wondered why the schematic showed separate symbols for the two paths, but understood from other posts that this was perhaps a better way to join all - I assume this may help keep any electrical interference from the audio side.)

I will also look into your advice on the RCA wiring, makes sense thanks.

 

Update on last couple of days:

I decided to power up the supply, then each channel individually.

I don’t  have a dim light set-up but figured low risk of short as this was working before and the changes I made were fairly straightforward.

I used a mains power adapter with built in consumption display, removed all fuses from the 2 audio channels and switched it on! I measured 65V + and - on each rail and noted .28A AC current draw. Fairly happy with that.

Starting with the right channel I connected my ammeter in series where fuse F2R would normally plug in and inserted the companion fuse. 
I switched on and measured 310mA , 62VDC and .7A AC current.

Bias is a little high, aiming between 250-300mA. But decided to leave as is for now and compare to left channel .

I tried to use my second ammeter but realized in the process it had a blown fuse so no good for current.

each time I made changes with my connections I would power down first and check the discharge of the main caps. 
Ok testing Left Channel bias and I have an issue! It is reading only 32mA and does not change much when adjusting trim pot. 
There must be a poor connection or something obvious as it is basically off and not idyling. 
I realized two things at this point, a. I should have ran these tests before stripping down the amp; b. I should have started testing before mounting the PCBs onto the heatsinks. I can’t see anything obvious on the surface. I started to re-check all resistors starting with those around the bias pot. I was almost done and finally noticed a broken wire underneath the PCB leading to the FETs.

 

aah I should have spotted that! Must have broken when I mounted the board and could not see it underneath.

Cut and re-stripped the end and soldered to the board - cleaned up another while at it.

tested Bias again and now at 300mA - much better.

Adjusted each channel to 290mV - little high but I am ok with that for now.

 

Finally I can move onto DC offset. All fuses are in.

Right channel measures 6mV - happy with that!

Left channel is 235mV !! Way too high!

So, onto matching transistor pairs …

 

Pics below of green broken wire, testing transistors and colour coding them …

 

IMG_1116.thumb.jpeg.bc5edb0437264b90f514265edeb0f8ef.jpeg

IMG_1138.thumb.jpeg.f381c17ea5a0c4ba1f10dc62deaadd6f.jpegIMG_1139.thumb.jpeg.09235720ebc824b90a497c44697c8a30.jpeg

  • Like 1
Posted

I’m having some challenges with the DC offset on the left channel. I started at 235mV.

replaced R4, 5 and 21 - these were 2-3% , No change, still 235mV.

Replaced R11 and 13 , 39k7 and 38k9 should be 39k … offset came down to 190mV.

onto transistors next as balance of resistors test ok.

replaced Q1, 2  with matching pair at 152 HFE…. Offset dropped to 63mV (original pair measured 70 and 98 - so not even close)

Looking much better, but aiming below 50.

replaced Q5, 6 with 160 HFE (old pair was 91 and 102)

BUT still 63mV.

I believe that these pairs only have to match individually, that not all 4 need to be the same. Need to confirm for this design.

went on and swapped Q3 and 4 , but did not match, 153 and 161 each.

again the don’t believe these have to match

DC offset drops to 55mV … really close now

 

decided to recheck bias… LCH 265mA so came down, set RCH same around 263mA.

removed ground from centre of main filter caps to chassis as recommended… but it appears I have -19VDC offset now??!!

when I put this ground back I am at 8mV right ch. and 152mV left. Something weird is going on.

Definitely looks like it wants that bridge … I will have to look into this grounding some more. I know there are two camps out there on making the bridge to chassis and I think DH220 had a similar change .. will do some more homework.

 

 

 

 

 

  • Like 1
Posted

Yep! What I suspected, with the bridge removed from chassis star ground to power earth between main caps I had to rely on the ground through the board from output terminal 6 to input terminal 2 via resistor R39.  Testing with my meter I don’t get a through circuit here across this 0.5 Ohm resistor. Pulled the resistor and sure enough it is open circuit, on both boards. 
Need to get some replacements tomorrow and drop them in! Will sleep ok tonight for now, then back to the DC offset. 
IMG_1152.thumb.jpeg.b4e54ed0ebd65f94972b39c5ab195215.jpeg

 

  • Like 1

  • Recently Browsing   0 members

    • No registered users viewing this page.

×
×
  • Create New...
To Top