Yep. Good catch!That must be a typo as I'm sure you meant the KSC1845F.
HARMAN Kardon 930 Restoration Process
- Thread starter mcaddie7
- Start date
mcaddie7
Active Member
Thank you for this wonderful explanation. I plan on reading your guide today on my lunch break. Also apologies for the multi threads, I get a little over zealous at times.
For any future users the following caps have been ordered along with some new trim pots. Transistors ordered for tone and amp board are as follows:
| Matching Pair: | Replacement |
| 2SA564A (x2) x2 - PNP | KSA992FBTA -PNP Link: https://www.digikey.com/en/products/detail/onsemi/KSA992FBTA/3163196 |
| Single | |
| 2SC828 x2 | KSC1845FTA - NPN |
Tone Board:
| 2SC828 (x2) - NPN | KSC1845FTA - NPN |
| 2SC644 (x6) - NPN | Link: https://www.digikey.com/en/products/detail/onsemi/KSC1845FTA/1047631 |
I'll update this thread next week when all parts arrive. Once installed we'll have to do adjust bias and we SHOULD be all set.
I'd suggest buying plenty of these as the ones you use in this position on the board must be matched. Twenty, maybe even thirty should be enough to get two closely matched pair if you are going to do both channels.
As for the 1845's, they are what I call a 'go to' transistor and are a common sub for many different transistors. It wouldn't hurt to have a healthy stash of these ones on hand either just in case you work on more receivers in the future.
No, he's not so great.
See here: https://audiokarma.org/forums/index.php?threads/can-anyone-tell-me-about-hifiaudio.1032226/
mcaddie7
Active Member
Learned this the hard way. Long story short I found for the second time he forgot even more caps and gave some incorrect ones. I asked if he could send these and didn't receive any response. Ebay wouldn't give any money back, so when I asked for a return from him I got reported. I then left a review of his service (was completely kind but honest) he flagged my review as "Derogatory" and it wasn't posted. Had to go through my credit card company to get a refund. Would absolutely nor recommend, guy is a con artist.
Anywho.....
Completely recapped the tone board and while I was in there swapped out all transistors with the ones Dlucy recomended. Before putting the tonebaord back I plugged it in and the Highs are noticeably brighter and beautiful. The bass was not quite as punchy as before but I also haven't biased anything yet, nor let the caps burn in (seems like bass does get better with time).
I'll post pics and my work on the amp board new transistors this weekend.
While I agree with you on buying in bulk, it's not really practical for some. If that's the case, purchase them on taped reels, usually indicated by TA at the end of the part number. You're much more likely to get them all either matching or very close in hFe because they are likely all from the same production run. Sort of a way to hedge one's bets. Also a good plan if one doesn't have a tester that can measure hFe.
Well yes, but then again no.
In theory that should be the case but in a recently purchased lot of twenty KSA992FTA's, the hFE varied considerably while being measured in a controlled environment. Since these transistors are being used as the differentials in the HK 930 and 630's I'm working on, I wanted them to be matched as close as possible.
On my last Mouser order, I bought thirty more and I'm glad I did. Same thing, I didn't take note of the Vbe, only hFE. At only 15 cents each, maybe I'll buy a hundred of them next time.
Exactly. I'll try to dial in the next set a bit better for a burned up 630 sitting on the bench right now as I might want to keep it for a while.
mcaddie7
Active Member
Update:
So tone board was completely recapped and all transistors replaced with the ones mentioned above. Checked resistors and they were all very close barring three but the amp sounded amazing from a quick turn on. Put tone board back up in and buttoned up a cleaned and polished faceplate
Before changing transistors on Amp board I wanted to bias the amp. I replaced both pots with multi turn pots.
With source selected set to Aux, and speaker 1 on and my resistors in the back, I biased to 15mv. However, the left side would only go up to 6mv, and if I increased or decreased the pot the bias would then go down.
Any tips? Thinking one of the transistors is going bad? The amp physically sounds fine but I’m guessing it could sound better if I found the issue?
So tone board was completely recapped and all transistors replaced with the ones mentioned above. Checked resistors and they were all very close barring three but the amp sounded amazing from a quick turn on. Put tone board back up in and buttoned up a cleaned and polished faceplate
Before changing transistors on Amp board I wanted to bias the amp. I replaced both pots with multi turn pots.
With source selected set to Aux, and speaker 1 on and my resistors in the back, I biased to 15mv. However, the left side would only go up to 6mv, and if I increased or decreased the pot the bias would then go down.
Any tips? Thinking one of the transistors is going bad? The amp physically sounds fine but I’m guessing it could sound better if I found the issue?
mcaddie7
Active Member
Bump
hello,
i had this untunable bias problem on a HK 730, stabistor was failing though diode tested ok.
try exchanging KB265 stabistor diodes from faulty left side with the ok right side ones...
if it solve the problem you can replace each with pair assembled 2x 1N4148 in series
though direct replacement with 1N4148's in series is faster option...
i had this untunable bias problem on a HK 730, stabistor was failing though diode tested ok.
try exchanging KB265 stabistor diodes from faulty left side with the ok right side ones...
if it solve the problem you can replace each with pair assembled 2x 1N4148 in series
though direct replacement with 1N4148's in series is faster option...
mcaddie7
Active Member
Hi! I'll try this out tonight when I go to dig in and replace the matched transistors. I do have a question though, why does the schematic show D621 and D622 being in parallel but when you look at the actual board / board schematic there is just one diode present on the Amplifier board? Also, when I get the replacement, do I put two of them in parallel to replace this or series? Any help is appreciated, thanks!
imho if there is no problem with them (faulty or known to fail with collaterals damages) let the genuine matched transistors...
you know the words "if it's not broken don't try to fix it" .... is even more valuable on these vintage materials.
one KB265 can be replaced by 2 x 1N4148 in serie so if there is only one KB265 great as it's simpler
after desoldering test your KB265 to have Vf , should be arround 1,3V
you know the words "if it's not broken don't try to fix it" .... is even more valuable on these vintage materials.
one KB265 can be replaced by 2 x 1N4148 in serie so if there is only one KB265 great as it's simpler
after desoldering test your KB265 to have Vf , should be arround 1,3V
mcaddie7
Active Member
Found the ones From the schematic actually, they are off to the side above the output transistors. Would love to know why but guessing it has to do with heat.imho if there is no problem with them (faulty or known to fail with collaterals damages) let the genuine matched transistors...
you know the words "if it's not broken don't try to fix it" .... is even more valuable on these vintage materials.
one KB265 can be replaced by 2 x 1N4148 in serie so if there is only one KB265 great as it's simpler
after desoldering test your KB265 to have Vf , should be arround 1,3V
For the transistors, I have a DC offset (non adjustable on this model) of 120mv each channel so I thought changing them out would lead to a cleaner sound.
yes they have to follow the heat of transistor to stabilise bias.
you can ad a 500ohms trim pot for DC Offset adjustement at R608 and R628 instead of 330ohms resistor
you can ad a 500ohms trim pot for DC Offset adjustement at R608 and R628 instead of 330ohms resistor
HK-930 Dc Offset Voltage problem
After reading the thread by EchoWars I tested DC offset, unfortunately all was not good, Left 29mV Right 124mV. After some great advice and info from EchoWars & Ecluser I have started a new thread as it is more specific to the 930. It appears there is no adjustment for offset voltage, so the...
audiokarma.org
mcaddie7
Active Member
Thanks for the DC Offset post.
So I changed all transistors on the board that Dlucy and Co. suggested. This brought the offset down from 120 to around 35-40 in both channels I’ll play around with resistor values to finish it off.
I then checked bias and dammit, the left side is still stuck at 6.6 mV. I checked both sides diodes but unfortunately lost one after taking these pictures so I must wait until my order comes in.
I ordered these, hopefully they are okay?
So here’s what was in the receiver for those that might get more out of the readings than for the two diodes.
Right side (good bias):
Left side (this was different if it matters. It’s the side I can’t bias):
So my real question at the end is, do I use two of the bought diodes for each one I took out (4 total per side) or one for each (two per side)? There were two on each side that I removed as suggested. Order should be in tomorrow.
yes 2x 1N4148 in serie are known tested replacement for such stabistor.
readings on your tester should be near the same for both KB265,
your left chanel stabistor show tiny lower ok Vf but with abnormal difference 16x higher testing current > trash bin !
as stabistor forward voltage (Vf) is arround 1,4V and 1N4148 is arround 0,7V so
you need >2x< 1N4148 in serie to replace >1< stabistor KB265 diode
replace each KB265 on your board by 2 x 1N4148 in serie et voilà
i can't be more clear than that
readings on your tester should be near the same for both KB265,
your left chanel stabistor show tiny lower ok Vf but with abnormal difference 16x higher testing current > trash bin !
as stabistor forward voltage (Vf) is arround 1,4V and 1N4148 is arround 0,7V so
you need >2x< 1N4148 in serie to replace >1< stabistor KB265 diode
replace each KB265 on your board by 2 x 1N4148 in serie et voilà
i can't be more clear than that
Last edited:
mcaddie7
Active Member
Diodes came in today and installed them on both sides, screwing this back into the heatsinks.
Once installed I then went to bias again, where both sides now hung around 9mv max. Letting the receiver warm up for 15-20 minutes while I made pizza they then settled out with a max of 15mv with the speaker button pressed inwards (allowing signal path to 8ohm resistors on output), and around 13 mv without the speaker button pressed in. Anyone care to explain why my max is around what is wanted for bias, and I can't actually get it to go over with the pot? It just goes up to 15, and if I keep turning it goes right back down.
Anyways! Checked offset and it is still down from 120 to 40 on each channel with new transistors installed.
Hooked it up and damn, even with the offset still a little high this thing is inky blank in the background. Not that it was loud before but it's just dead silent now. I will say the bass is everrrrrrr so slightly neutered compared to what it was but perhaps this will take time to come back (is burn in real?) or it could just be the Citation 11 I have it plugged into now being the culprit of this slightly change.
Next up:
Install proper resistors to adjust offset to 0 as best I can.
Remove output transistors and add new thermal paste.
Install LED lights that are coming in.
Change resistors on amp board if I'm feeling ambitious.
Recap FM section though I really won't and don't use it.
Once installed I then went to bias again, where both sides now hung around 9mv max. Letting the receiver warm up for 15-20 minutes while I made pizza they then settled out with a max of 15mv with the speaker button pressed inwards (allowing signal path to 8ohm resistors on output), and around 13 mv without the speaker button pressed in. Anyone care to explain why my max is around what is wanted for bias, and I can't actually get it to go over with the pot? It just goes up to 15, and if I keep turning it goes right back down.
Anyways! Checked offset and it is still down from 120 to 40 on each channel with new transistors installed.
Hooked it up and damn, even with the offset still a little high this thing is inky blank in the background. Not that it was loud before but it's just dead silent now. I will say the bass is everrrrrrr so slightly neutered compared to what it was but perhaps this will take time to come back (is burn in real?) or it could just be the Citation 11 I have it plugged into now being the culprit of this slightly change.
Next up:
Install proper resistors to adjust offset to 0 as best I can.
Remove output transistors and add new thermal paste.
Install LED lights that are coming in.
Change resistors on amp board if I'm feeling ambitious.
Recap FM section though I really won't and don't use it.