TEAC A-H500 Lights up No Sound

mbose

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Just learning still but trying to fix this for a friend and hoping it's something I can do. Would appreciate any help beyond the user and service manual which I have.

This is a very clean unit. I cannot tell if anyone has been into it before, but there are blue felt tip pen marks on each of the power supply caps and similar red marks on many of the main board caps. I do not have the remote.

Here's the symptoms:

-- In standby mode and high volume there is bleed-through with CD input regardless of which source is selected. I am "guessing" that this is normal.

-- The protection relay engages instantly when the unit is turned on (no delay). This may be normal, but I haven't seen one of these units before and don't know.

-- Once turned on, the amp is dead quiet at the speakers and headphone output regardless of source, tape settings, or volume level.

-- The CD Direct light stays engaged and does not respond to being pressed.

Diagnostics I have been able to do so far:

-- CN55/56 on the power supply board read -38/38. Service manual says it should be 36. I don't know if this is enough of a difference to be a problem, but leads me to believe problem is not in the power supply?

-- Bias current at CN59/60 on the power amp boards was very high, between 35-40 mV. I was able to adjust with VR53/54 to the recommended 11mV.

No changes to symptoms. Not sure where to go next and hoping these symptoms sound familiar to someone. Schematics attached.

Thanks,
Michael
 

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  • hfe teac a h500 service schematics small.pdf
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On connector BN91 check pin 3, that is relay control for cd direct. Also may want to follow that back to the control IC and check the voltage on the pin. Try switching sources while checking the voltage there and see if anything changes. If not, check supply voltages to that IC, if good you may be dealing with a bad IC.
 
it will be a bad function switching ic or 2 . i had the same with my ah-300 . it was caused by hot plugging rca inputs .
 
Thank you both!

@stillspin'n, going to check B91 as suggested.

@petehall347, can those switching ICs cause the amp to not output sound on all sources even if only some of the ICs are bad? Is there a way to test them or is it just best to replace all 5 (assuming you mean the LC4966s at IC12-16?)

Thanks!

Michael
 
bleed-through with CD input regardless of which source is selected .sort of confirms it .
voltage checks at the ic.s pins should tell you if something wrong .
i remove the solder on the power pins then inject a signal to ic outputs .
i seem to remember to the cd direct light too .
 
Thanks again, this looks doable for me. Sorry for one more question, but before jumping in, I wanted to make sure I was clear that there is only bleed through when the amp is on standby, and only at max volume. Once the amp is turned on, there is no sound regardless of which input is used or selected.
 
looks like there is another fault with yours as it shouldn't play any sound when switched to standby .maybe you got mixed up ?
 
Sorry, you are correct! Bleed through is only with RCA input to CD, amp on, volume on high, and any source selected. CD direct stays lit, cannot turn off. Checking that IC as suggested.
 
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