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Tandburg 2080 restoration problems

Alright I've got an update, I sat down with the schematic double checked all the wiring. I had a couple plugs for the lights switched, and one for the power reading and mode filter board. I've checked all the other wiring and thought I figured out the problem but now when I power it on theres no lights at all and no sound. I'm not sure where to go from here. I spent a few hours with the schematic and check every wire harness so I'm 99% sure I have the wires in the correct place now but it's really strange that I had lights and at least distorted sound before fixing the plug arrangement but now no lights and no sound... anyone have any suggestions on where to check next?
 
Heres another small update, if I remove the clip from the poweramp board and power on I hear the relay click. With the power amp board connected there is no click besides the power button itself when I turn it on...
 
Also when I check the 25v rail its show 38v now even while being plugged into the DBT. When I try to adjust this setting the pot has no effect on the voltage
 
Alright, one more update and I think I'm gnna call it a day and dig back in another day. I'm starting to get frustrated with it and think I'd be better off starting fresh another day.
I've got the lights working again, looks like there was a couple leads on the riaa board got bent and a couple were touching the heatsinks. I got everything put back into place and made sure none of the leads were shorted. I hooked it up to the DBT which immediately went dim and about 2-3 seconds later it would flash and make a thump sound from the speakers. Seems strange that it would flash and get dim again instead of staying bright. Not sure what that points too but I'll get it back out in a day or 2 and get back to troubleshooting. In the meantime if anyone has any ideas I'm all ears haha
 
Also if I disconnect the power amp board the flashing and thump stops but I'm still reading 39v on the 25v rail and cant adjust it.
 
This is turning into a strange journey, pity since normally these receivers are very simple to troubleshoot. I'll spare you the rant but the short version is replacing a bunch of parts (involving disassembly and reassembly) isn't step 1 if you want to do it the easy way. Should have started with a simple assessment of power supply voltages, check for DC offset, other issues noted in the process etc. Maybe some of that was already done and not mentioned, or that someone ahead of you has buggered what is normally a user-friendly device to service

I'd stop banging away at the receiver at this point, and go through it logically and by section before something gets permanently damaged. Power supply (supplies), power amp status, source/regulator board, preamp/filter boards, tuner, RIAA section. You need to get some baselines in place in order to isolate and focus on the things that are causing problems.

What part of the country are you in?

John
 
Yeah, I'll admit I'm not the best st troubleshooting. I usually find semi-working units and restore them for stability. I usually only mess with my own gear because I know just enough to be dangerous haha. My friend practically begged me to try to fix this tandberg tho because there are no audio repair places within like 3 hours of us. I'm located in WV btw.

Heres the history that I know on the receiver, my friend was given this receiver by his neighbor. We are the first people to mess with it in 10 years or so I believe. He said the neighbor told him that he was listening to it aroumd 10 years ago he walked out of the room, heard a loud pop and whem he ran back into the room there was a little bit of smoke coming out of the vents and no more music. He put it away and said he hasnt touched it since, however when I was working on it the power amp board definitely appears to have been tampered with.

So fast forward 10 years and my friend shows up at my workshop with this basket case, says he turned it on and it lit up but no sound. I told him it wss stupid to do so without at least hooking up a DBT but I've been using my tester since it showed up here.
 
When it first got here I noticed the dead festoon fuse and really hoped that it had just died from old age and would be a simple fix. So I ordered a 10 pack just incase along with replacement caps for the program select board, power amp board (minus the large filter caps), and preamp board. I changed the 1000uf cap and fuse light. Powered on and altho my tester wasnt glowing the fuse bulb was very bright and actually blew at one point while I was testing. I got a little impatient at that point and decided to change out the rest of the caps I had to see if I had anymore luck. At this point the fuse light stopped lighting so brightly butni could only get clear sound if I bypassed the preamp. That's when I made this post and pretty much everything else I've done has been documented. The only voltages I've taken have been on the 25v rail but after getting all the wires moved to the correct places (D'oh!) Its acting crazier than ever!
 
Oh I also forgot to mention that when watching the 25v rail the dbt starts dim while the voltage climbs to around 38v and when it makes the thump sound, the dbt lights up and the voltage drops down to around 25v then climbs back up. It will do this continus cycle like this until I turn it back off. I only let it cycle twice before I shut it back down.
 
Something very wrong there. Are you anywhere near SoCal? I could sort all that out in a couple hours but it's much easier to do with it front of me than remotely. I don't do customer repairs anymore but I also hate to see these pieces get damaged or become unsalvageable.

The festoon lamp is not a fuse, BTW - it is just a lamp, used to current-limit the regulated supply. There's an actual fuse (smaller GMA type) on the same board that is the actual fuse, may want to check to see if the value on that has been changed from spec.

Any chance you swapped the plug 180 degrees that connects that small regulation transistor on the cross-member to the source/regulator board? I couldn't tell for sure from the pics... but I've never seen the +25V rail change by itself, it's often not set 100% accurately (can change over time etc.) but it should not be wandering up and down, ever.

It sounds more like there's a big DC offset issue, seems like it tries to come out of protection/thump/short or offset across the output stage pulls a bunch of current, DBT lights up. But your description of the 25V rail increasing doesn't really fit that scenario nor should it come out of protection in the first place if there's that much DC offset.

John
 
Unfortunately I'm clear on the other side of the country in west Virginia. I double checked that connector for the chasis mounted transistor and it's in the correct orientation. If i disconnect the speakers the cycling stops but the voltage remains at 39v and is unable to be changed no matter how far I turn the variable resistor. The orignal readings I gave at the beginning of the post were with a few of the plugs swapped on the regulator board.
 
Oh and I double checked the fuses, they are all the correct rating. If you have the time I'm more tha happy to follow whatever instructions you have for the next steps in troubleshooting, I'm just at a loss for where to go from here. I've restored or repaired around 20 pieces of gear and have never been given this much trouble. Granted most of it was pretty simple tube stuff but man this tandberg is giving me a headache haha
 
I was originally doin the job for fun and possibly a 6 pack of beer but if I ever get this thing figured out we might have to up the price to a bottle of nice bourbon!
 
Oh heres something! I found a blown diode number cr606 on the regulator board. Would that cause some of the problems I'm seeing?
 
Yes, at least if open circuit it causes the regulator not working anymore and having the 38 volts, as there is no path to the zener regulator diode. So the regulator transistors goes in full conduction and now just pass whatever comes in.

A "little" problem may be the fact that the chance is remote it did "blow" without other parts damaged/shorted.

Myself I would consider check all three transistors and all those diodes using a DMM on diode check setting (of course, having the receiver not plugged in the mains...).


BTW, At a first glance it looks to me, if you unplug J901 then the main amps get no power, doing so makes it much more safe to work on the problems/measuring without damage.

good luck!
 
Well I checked my stash and had one on hand. After changing it all the previous symptoms remain and now the festoon bulb glows incredibly bright (still on DBT) and theres a bit of smoke coming from the area where the diode I changed is
 
I checked all the diodes on the board and only the one gave me a bad reading. I'm going to check the transistors now. Luckily I have a small transistor tester I can use for that. It's just a matter of safely removing them.and testing.
 
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