Need alternative to Zener Diode HZS4C-1TD

Thread Starter

K3YHL

Joined Jan 6, 2019
11
Hi everyone, i'm new here and this a probably a really basic silly question but although I have good knowledge & understanding of many types of PCB components I am struggling with Diode properties.
I'm looking for a replacement for a HZS4C-1TD zener diode which are very hard to find. I do have some 4.3V & 7.5V 1/2 watt BZX55C zeners and have tried to compare both data sheets but am worried that they wont be compatible. I think the 4.3V ones would be a match but would appreciate the more knowledgeable of you out there to confirm this for me.
Going forward it would be good to know what I need to be looking for in the data sheets to match up any future alternative diodes
I work a lot on repairing vintage electronic equipment and so regularly struggle to find the OEM parts.

Thanks in advance
Key
 

ericgibbs

Joined Jan 29, 2010
13,819
hi k,
Welcome to AAC.
This PDF is for the HZS series.
Check the Zener diode type.

E

EDIT:
Do you have a circuit digram of the equipment you could post.??
 

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Thread Starter

K3YHL

Joined Jan 6, 2019
11
hi k,
Welcome to AAC.
This PDF is for the HZS series.
Check the Zener diode type.

E

EDIT:
Do you have a circuit digram of the equipment you could post.??
Hi Eric, the HZS4C-1TD diodes are from the amp board on a Denon AVC-A10SE I have the service manual for the amp and these are the correct ones but are unavailable.

Key
 

ericgibbs

Joined Jan 29, 2010
13,819
hi Key,
If we could check the section of the circuit where the 4.1Vz is connected, we may be able to suggest any change that maybe required in order to use a 4.3Vz or any minor modification.
E
 

Thread Starter

K3YHL

Joined Jan 6, 2019
11

bertus

Joined Apr 5, 2008
21,585
Hello,

Looking at the schematic part, TR802 makes a rubber diode, it is adjustable between 2.64 and 3.34 Volts using VR702.
TR802 is likely mounted on the heatsink of the powertransistors.
Make sure that the connections of CW935-CZ935 are OK.
It looks like this circuit has failed and blew up the rest of the circuit.

Bertus
 

Thread Starter

K3YHL

Joined Jan 6, 2019
11
hi,
I would agree a 4V zener say 500mW would be a suitable replacement.
E
Thanks chaps, one of the 1Kohm resistors had completely blown (R814 i think), it was completely black and almost powder.
Everything else is back on the board now awaiting the diodes so wont be long until that magic moment when I flick the switch and hope!

Appreciate your help

Key

LOL, i know Bertus but I'm building up my stocks :). prefer to buy from them rather than the Auction sites so I know i'm getting quality genuine parts.
Will have a look at CPC though.
 

MisterBill2

Joined Jan 23, 2018
9,439
With all of those components failed it is clear that there must have been some reason for the massive failure. Have you located the reason that all of those parts were destroyed? It looks a lot like the parts damaged are in the bias setting circuit for the direct coupled output stage of a power amp, and if the supply voltage gets too high then the whole thing is destroyed. The temperature compensating diodes are a critical part of the circuit, for sure.
So it is vital to repair the portion that caused this failure before turning on the power, since you don't want to destroy things a second time. That is the HUGE problem with the whole direct coupled amplifier concept. One failed capacitor or leaky transistor in the early stages will destroy most of the expensive components downstream.
 

Thread Starter

K3YHL

Joined Jan 6, 2019
11
With all of those components failed it is clear that there must have been some reason for the massive failure. Have you located the reason that all of those parts were destroyed? It looks a lot like the parts damaged are in the bias setting circuit for the direct coupled output stage of a power amp, and if the supply voltage gets too high then the whole thing is destroyed. The temperature compensating diodes are a critical part of the circuit, for sure.
So it is vital to repair the portion that caused this failure before turning on the power, since you don't want to destroy things a second time. That is the HUGE problem with the whole direct coupled amplifier concept. One failed capacitor or leaky transistor in the early stages will destroy most of the expensive components downstream.
I believe it was one of the main output transistors than gave up the ghost, (TR804 & TR806).
I am still an amateur at this but have worked outwards from every part that had blown until i came across one or two that were still in tact.
Not guaranteed to spot all the issues but fingers crossed.
I hope to eventually purchase an oscilloscope and teach myself how to test circuits using this.
 

MisterBill2

Joined Jan 23, 2018
9,439
I believe it was one of the main output transistors than gave up the ghost, (TR804 & TR806).
I am still an amateur at this but have worked outwards from every part that had blown until i came across one or two that were still in tact.
Not guaranteed to spot all the issues but fingers crossed.
I hope to eventually purchase an oscilloscope and teach myself how to test circuits using this.
Half of the problems, including failed power transistors, were caused by components far upstream in the direct coupled amplifier circuit. So I am suggesting being very cautious when first powering up after the repairs are done. That includes knowing what voltages you should be seeing at the various points and checking to make sure that what you actually have is correct, And before power on, use your meter diode check function to verify that all of the small transistors are good and that none of them are short-circuited collector to emitter. That is an easy way to save yourself quite a few dollars.
 

Thread Starter

K3YHL

Joined Jan 6, 2019
11
Half of the problems, including failed power transistors, were caused by components far upstream in the direct coupled amplifier circuit. So I am suggesting being very cautious when first powering up after the repairs are done. That includes knowing what voltages you should be seeing at the various points and checking to make sure that what you actually have is correct, And before power on, use your meter diode check function to verify that all of the small transistors are good and that none of them are short-circuited collector to emitter. That is an easy way to save yourself quite a few dollars.
Ok thanks, ill do some more testing before flicking the switch.

Thanks for the advice.
 

bobelis

Joined Feb 15, 2019
2
Ok thanks, ill do some more testing before flicking the switch.

Thanks for the advice.
Hi, I have only now seen your post. I am also seeking the same diode but have had no luck. I have checked the circuit for the AVC A1SE which is almost identical. it uses a hzs4b-2, 3.9v and a hzs4a-1, 3.5v. I will use the 3.9v zener. have you had success with your unit? Regards, Bob.
 

Thread Starter

K3YHL

Joined Jan 6, 2019
11
Hi Rob, yes i had success but only after following the advice from the chaps above. I also found TR907 (2SC4511) to be shorted on the regulator board. The Diodes suggested did the job and the only problem now is that I have no rear left output :-( .
Completely separate issue though and one that ill get around to once I've worked through the other 7 amps that I have stacked up in my office!
 

bobelis

Joined Feb 15, 2019
2
Hi Rob, yes i had success but only after following the advice from the chaps above. I also found TR907 (2SC4511) to be shorted on the regulator board. The Diodes suggested did the job and the only problem now is that I have no rear left output :-( .
Completely separate issue though and one that ill get around to once I've worked through the other 7 amps that I have stacked up in my office!
Hi, Sounds familiar. I have a AVC A1SE which I repaired a few years back. also another, which I bought before last Christmas, which has a shot DSP board. it seems that the whole series have trouble with heat related solder failure mainly at the 2SC4001 and 2SA1545 terminations. pay particular attention to all these should you pull it apart again. the tracks are very close in these areas so watch out for solder bridge. I was caught even though I checked with a eye glass. Regards, Bob.
 
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