This amp was previously repaired in 1995.
From the looks of it, someone know what they were doing so this amp was handeled by someone with experience. That being said they should have used some acitone. Looks like a previous blow-out was repaired with modification; TIP102 transistors sitting on legs 1&2 of several of the TIP35 outputs, and then in which Q303/Q307 was recovered (Left of photo).
When I opened I saw the the affected area but it looked repaired enough for me to continue testing. The amp powers but plays with a very low volume static on the speaker terminals and it is audible and visible on the scope.
Its also as if the previous repair wasnnt ever finished as the bias pots were also way out of adjustment and way too far counter clockwise. Properly adjusting them made a bit of difference in the output static; but the best thing I did to help it out was grounding the RCA shields - the amp plays clean and clear then.
Once I figure out the faults I'll also have to replace 12x IRFZ44 in the power supply as the one on the edge let out some smoke (not by me) and was likely damaged slightly during previous repair. I removed this fet. I guess I'm lucky the rest of the power supply survived.
From the looks of it, someone know what they were doing so this amp was handeled by someone with experience. That being said they should have used some acitone. Looks like a previous blow-out was repaired with modification; TIP102 transistors sitting on legs 1&2 of several of the TIP35 outputs, and then in which Q303/Q307 was recovered (Left of photo).
When I opened I saw the the affected area but it looked repaired enough for me to continue testing. The amp powers but plays with a very low volume static on the speaker terminals and it is audible and visible on the scope.
Its also as if the previous repair wasnnt ever finished as the bias pots were also way out of adjustment and way too far counter clockwise. Properly adjusting them made a bit of difference in the output static; but the best thing I did to help it out was grounding the RCA shields - the amp plays clean and clear then.
Once I figure out the faults I'll also have to replace 12x IRFZ44 in the power supply as the one on the edge let out some smoke (not by me) and was likely damaged slightly during previous repair. I removed this fet. I guess I'm lucky the rest of the power supply survived.
Last edited:
You need to remove all 5 of those caps to see how much damage there is. Is there any evidence of corrosion under the board?
Any of the PF(M) or PL(M) caps are suspect in hifonics and autotek amps (or anywhere else that they were used).
Those caps aren't likely to be causing the static but if it's a random sort of noise that sounds like popping or crackling from time to time, I would suspect that one or more electrolytics are leaking (in the audio section).
Any of the PF(M) or PL(M) caps are suspect in hifonics and autotek amps (or anywhere else that they were used).
Those caps aren't likely to be causing the static but if it's a random sort of noise that sounds like popping or crackling from time to time, I would suspect that one or more electrolytics are leaking (in the audio section).
Im really not too sure why the TIP102 transistors were added; but the area in the first photo on the left had moderately burned and was obviously repaired. I really dont want to touch the repair as it seems the amp works how it was done. I just gotta fix the scratching noise and the power supply and test it for reliability.
Without any schematics is always tough to work on these Zed amps.
Without any schematics is always tough to work on these Zed amps.
I have seen this before on ZED amps. TIP-102's and 107's are used throughout the series to drive the much larger and harder to drive D100 and D200 Darlington BJT rail supply level switches. Your amp appears to be one that did not have them designed into the board circuity schematics and they were most likely added by a Zed tech, IMO....
Zed used TIP102's and 7's for many years in these three stage supplies. Although the PC Board lacks the positioning for the device its nothing new to see them added like this. It may be just a PC Board layout error that was corrected at the time of build probably by Zed's crew. Factory parts, just installed funny.
Again this is my opinion after seeing these for 25 years...
I think I found the issue with one of the caps on one of the rising boards so I replaced it with a spare for testing.
I'll still need 12 x IRFZ44 for the power supply. Is there any variance to a Z44? I see Digikey has several at different prices like Z44V, Z44N, Z44E, Z44R... Only the most expensive Vishay part from Digikey is a straight Z44. Can I use any of the others? I think I've interchanged these before with another amp at one point... They all have different "Max power" ratings, but everything else is similar.
I'll still need 12 x IRFZ44 for the power supply. Is there any variance to a Z44? I see Digikey has several at different prices like Z44V, Z44N, Z44E, Z44R... Only the most expensive Vishay part from Digikey is a straight Z44. Can I use any of the others? I think I've interchanged these before with another amp at one point... They all have different "Max power" ratings, but everything else is similar.
I'll have to check on the rail voltage. The noise is present on the scope whether I ground the scope to amp ground or non-bridging terminals.
I'm about to throw an order over to ActiveParts for a 50pc quantity of IRFZ44N transistors. They look legit. Ever use them before? activeparts items - Get great deals on Business Industrial items on eBay.com!
Maybe theres a better place to buy these elsewhere...
I'm about to throw an order over to ActiveParts for a 50pc quantity of IRFZ44N transistors. They look legit. Ever use them before? activeparts items - Get great deals on Business Industrial items on eBay.com!
Maybe theres a better place to buy these elsewhere...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.