Looking for TEAC AV-H500 amplifier schematics or service manual - Page 1
Forum section: electronics / repair

author: oldway
author_rank: Super Contributor
timestamp: February 22, 2017, 02:04:27 pm
content: I am repairing a TEAC AV-H500 amplifier but I did not find schematics.First, there was no output in none of the 4 channels.All the drive circuits are under the dissipator and the electrolytics capacitors of these circuits where all bad because they worked at too high temperature.I subsituted all the 18 electrolytics capacitors and it came to life again....but I had very high output noise when I touched the preamplifier printboard.I found bad solders at the connector....I solved this.I found also bad solders in the two transistors from the protection circuit.I had another problem: the dissipator was getting very warm (about 80°C) and the amplifier was going in protection.To try solving this, first I lubricated the fan dc motor (Matsushita MDN4RB4MRC) who was making noise, then I increased the fan speed by changing a resistance of the voltage divider of CTN temperature sensor from 220R to 1K.It is still going in protection after about 10 minutes of working.I did not found any iddle current trimpot , nor any way to measure this iddle current of each of the 4 channels.Without schematics, I can't go further.Thank you very much for your help....

author: tautech
author_rank: Super Contributor
timestamp: February 22, 2017, 02:19:46 pm
content: Is this one OK ?https://elektrotanya.com/teac_a-h500_sm.pdf/download.htmlWait for "processing" to change to get manual.

author: oldway
author_rank: Super Contributor
timestamp: February 22, 2017, 02:21:00 pm
content: And now a new problem : it stays in protect all the time even with dissipator at ambient temperature.No that's not the same....I had already downloaded this one...thank you !The AV-H500 is a surround 4 channels amplifier, not a stereo amplifier.I looked the output circuit schematics, It's different.The A-H500 has trimpots to adjust iddle current, the AV-H500 does not.

author: oldway
author_rank: Super Contributor
timestamp: February 22, 2017, 02:56:21 pm
content: Some pictures:

author: oldway
author_rank: Super Contributor
timestamp: February 22, 2017, 02:59:27 pm
content: Not from meProbably an older repair that has be done by a NOT qualified technician....

author: tautech
author_rank: Super Contributor
timestamp: February 22, 2017, 03:04:17 pm
content: Then I found this one that my browser warns me might be dangerous:http://babodor.ru/28-06-2015-16.htmlCame from here:http://go.mail.ru/search?&fr=gogo&q=teac%20av-h500Which came from here:http://electro-search.ru/v.php?2009-11-01-99

author: oldway
author_rank: Super Contributor
timestamp: February 22, 2017, 03:11:47 pm
content: I found it too but I did not want to risk have problem with my computer....I think this TEAC is a very bad project and it's not worth it.Normally I only repair the vintage amplifiers but I agreed to fix it because it was a friend of a friend of mine who asked it to me.I should have refused, this amplifier is a crap, it is inaccessible, overheating, no test points, forced cooling with low quality fan, ... no way to compare with a vintage Marantz 2285B !

author: tautech
author_rank: Super Contributor
timestamp: February 22, 2017, 03:18:34 pm
content: Quote from: oldway on February 22, 2017, 03:11:47 pmAs yet I have not gone through all the manual providers listed in the manual sticky in the Repair board. It takes some time but sometimes can be worth the effort.Sometimes results do not show with Google, instead you must check the brand folders in each of the better manual repositories. I will check if you have found one later and look further if you haven't. (need sleep now)

author: mzacharias
author_rank: Frequent Contributor
timestamp: February 22, 2017, 05:32:51 pm
content: If the output transistors are all ok, check transistor junctions(drivers etc) and use a cheap multimeter with hfe function and check all the smaller transistors for gain issues. I have seen one Teac like this with zero gain on a transistor cause a DC offset on a given channel. (Since you have already disassembled you cannot check to see which channel is causing your issue). Check and correct any bad solder connections, and it should probably work. I hate these models, but I have had success fixing them.

author: oldway
author_rank: Super Contributor
timestamp: February 22, 2017, 05:57:11 pm
content: Thanks for your answer.As you can see on the picture, I have desoldered all the power transistors and I checked them with the component tester of my oscilloscope Hameg 605 (which is far better than with a multimeter) and they are all good.I have now reassembled the amplifier and there is no access to outputs because it stays in protection ....I can't measure dc offset on the loudspeakers outputs because output relays are open.There is no access to measure directly on the circuit board because it is very compact. (see pictures).There is no access to the solder side of the board because bottom plate is not removable.I already checked for bad solders when I replaced the 18 electrolytics capacitors and I reflowed a lot of them.I did not checked the drivers transistors for low gain, but I controlled the signatures of each one with component tester , comparing them between channels and they are the same.I wonder how they ajust the iddle current and DC voltage as there is no trimpot, nor for ajusting iddle current, nor for 0V dc output?Before asking for help on this forum, I obviously did a search on the Internet (google) and I did not find these schematics.Others besides me have also searched but in vain.http://www.diyaudio.com/forums/solid-state/152572-teac-av-h500-service-manual.htmlMy hope is mostly to find someone who has these schematics or service manual.

author: oldway
author_rank: Super Contributor
timestamp: February 22, 2017, 06:11:03 pm
content: If somebody knows this amplifier, perhaps he could answer some questions:Is it normal that the dissipator became very warm only with iddle current without output power ?At what temperature the fan began running ?At what temperature does the protection circuit do atuate ?Protection circuit seems very sensitive ...Is that normal ?How to know what fault did the protection circuit atuate ?I think there are different protections: overcurrent, DC output, overheating, ...If I had the schematics, I could test the main board separately feeding the board on the bench with my power supplies.But I can't do this without knowing exactly what I am doing.

author: mzacharias
author_rank: Frequent Contributor
timestamp: February 23, 2017, 12:20:24 am
content: Quote from: oldway on February 22, 2017, 05:57:11 pmOne measures the DC offset at the emitter resistor(s) with respect to chassis ground. One takes a quick reading before it shuts down.I often work on amps with no ready bottom access. Sometimes a ground path needs to be qualified but it can be done.Like I said - I hate these Chinese Teac's. They weren't designed to be repaired, as you have seen.The bias will usually be within spec if the amp is running properly.The service manual would probably mention something along the lines of snipping a jumper or a resistor lead if the bias needs to be reduced a bit.

author: oldway
author_rank: Super Contributor
timestamp: February 23, 2017, 04:13:33 am
content: With the kind of rectangular ceramic emitter resistor they used, It is not possible to reach the wires of the resistors to measure iddle current.See picture, you will understand.When reassembled, it is still worse ! No way to measure something on the emitters of power transistors !NB: There is one possibility: to let the power transistors be powered on for a short time without the dissipator and look for the transistors who are getting warm.I did not tried this because it is very risky.

author: mzacharias
author_rank: Frequent Contributor
timestamp: February 23, 2017, 01:08:35 pm
content: Quote from: oldway on February 23, 2017, 04:13:33 amThere a a fairly large 10 or so ohm resistor near each of those coils shown in your pics which corresponds to each channel output. You can measure there with respect to ground.I don't recommend running with no heat sinking.Didn't mean to mislead you regarding measuring at the resistors, but just look at almost any modern surround receiver schematic. There really isn't much difference between most of them. Pioneer, Denon, Yamaha, etc. From the output transistors looking backwards into their driving circuit you will have two driver transistors. Their emitters are usually connected together by a resistor of perhaps 150 to 330 ohms, across which is developed the driving voltage for the outputs. There will be a small value resistor (say 3.3 to 10 ohms) from each side of this resistor to the bases of the outputs. On the input side of the drivers there will be a bias transistor. Before that there will be a pre-driver or buffer stage, and before that a differential transistor pair.If there is a DC offset on one channel now you know where to focus your efforts. If there is a DC offset on ALL channels (assuming everything is connected and grounds qualified), suspect a power supply issue of some sort (like a bad fixed voltage regulator for example).DC on all channels can be a red herring if everything is not connected. Sometimes we miss connecting a ground here or there and this affects all channels.

author: oldway
author_rank: Super Contributor
timestamp: February 23, 2017, 03:09:32 pm
content: As it powers on normaly now, I could measure DC unbalance on all channels, doing it very quickly :Front left: 3.2mVFront right: 10.4mVrear left: 0.5mVrear right: 0.1mVcenter: 0.0mVIt goes in protect 5 seconds after power on....Iddle current of one or more channels is too high for sure....I powered it on for a very short time and the dissipator is already warm.Now, I can't power it on anymore, it goes everytime in protect.In my opinion, the only way is to check the main board and the protections board on the bench with an external power supply.But I need the schematics, or better, the service manual to do this.

author: RayRay
author_rank: Frequent Contributor
timestamp: February 23, 2017, 04:18:34 pm
content: From a quick look, the caps I marked in red don't look good to me:https://s3.postimg.org/sg7psympf/IMG_0873_B.jpghttps://s3.postimg.org/b47d7it83/IMG_0875_B.jpgNot sure that's dust or leakage on the first pic, but the top of both caps looks a bit bulged.And on the second pic, that cap looks a bit squished up/swelly on the top portion.I'd suggest you have those replaced and see how that goes.Generally speaking though, if replacing em wont do the trick, then you'd have to properly test all components til you find the culprit.

author: oldway
author_rank: Super Contributor
timestamp: February 23, 2017, 04:54:59 pm
content: These are just photo problems caused by the reflection of light. The capacitors are perfect, they are not bulged.The bad capacitors were below the heatsink, I changed 18 of themThe lateral printboard is the preamplifier, It has nothing to do with the problems: heatsink becaming too hot in a short time and amplifier going in protection mode.

author: mzacharias
author_rank: Frequent Contributor
timestamp: February 25, 2017, 11:16:04 am
content: Unfortunately I think I'm pretty much out of generic advice. I think I could probably fix it on my bench but like the original poster I believe a comprehensive service manual is now required. I will say the small (milli-volt) offsets mentioned would not trigger the protect. Maybe 1.2 to 2 volts would be required to trigger.

author: oldway
author_rank: Super Contributor
timestamp: February 25, 2017, 11:53:25 am
content: Anyway, thanks a lot for your help.....Max DC output voltage is generaly 500 mV.I am looking for the schematics because this is the only way to succeed troubleshoot and repair this amplifier.Nothing accessible, no way to measure something, without schematics, you go nowhere.As you said, this amplifier is not made to be repaired.I have many years of experience in repair and I think the only way to troubleshoot these faults is to dissasemble the amplififier, to feed the main printboard on the bench with an external power supply +/- 55V with current limitation and measure the bias currents of every power amplifier.As all driver circuits are below the heatsink and are not accessible, schematics and even service manual are needed to troubleshoot the faulty components.I already worked for more than 5 hours on this amplifier, I replaced 18 electrolytics capacitors and, without schematics,I can't go further.

author: jjoko
author_rank: Contributor
timestamp: May 03, 2020, 09:43:28 am
content: This is for reference...I was looking recently for the same service manual for this TEAC AV-H500 as the other posters here over the years and elsewhere...and finally have found it ! So just in case anyone else needs it in the future they can find this thread and here is a link!https://elektrotanya.com/teac_av-h500d.pdf/download.html