Seeking Advice on Diagnosing Vintage Amplifier Fault (Thermal Imaging Tools?)  - Page 1
Forum section: electronics / beginners

author: Eurora
author_rank: Contributor
timestamp: August 04, 2025, 03:49:40 am
content: Hi everyone,I'm a self-taught electronics hobbyist troubleshooting a vintage amplifier (left channel distorted, right channel normal). Here's what I've done so far:​​1. Diagnostic steps:​​✅ ​​Visual inspection​​:Capacitors show no bulging/leakingPCB shows no visible burns or damage✅ ​​Basic measurements​​:Power supply: ±25V (normal)Quiescent current on amplifier ICs (TDA2030A):Left channel: ​​22mA higher​​ than right channel✅ ​​Replacement test​​:Swapped left/right channel ICs – fault persists​​2. Current suspicion​​:Possible hidden failure in ​​low-value resistors​​ or ​​SMD transistors​​ causing thermal issues. Forum research suggests thermal imaging might help locate hotspots.​​3. My current tools​​:Multimeter (UNI-T UT61E)Basic oscilloscope (DSO138)​​Specific questions​​:Is thermal imaging ​​essential​​ for locating hidden heat faults? (Seen FLIR/HTI recommended)Will entry-level thermal cameras like HT-301 (250×250 res) work for ​​PCB-level diagnostics​​?Are there ​​cost-effective alternatives​​? (e.g., IR thermometer + thermal stickers)Thanks in advance for your support – I really value the expertise in this forum!

author: edavid
author_rank: Super Contributor
timestamp: August 04, 2025, 04:48:37 am
content: I think it's unlikely that a thermal camera would help you.Do you have a schematic?Have you checked the DC levels on the TDA2030 pins to see if the channels are different?

author: Grandchuck
author_rank: Super Contributor
timestamp: August 04, 2025, 01:39:10 pm
content: The TDA2030A data sheet shows quiescent current from 50 to 80 mA, so that is OK.Can you feed a sine or ramp wave in and post the output waveforms (both channels)?

author: benj38
author_rank: Frequent Contributor
timestamp: August 04, 2025, 03:41:40 pm
content: I second what@edavidsaid, and would even say it more bluntly:forget about the thermal camera!Signal tracing is your best approach. Given that it is a stereo unit, and one channel is fine, by comparing the signal (using your scope) and the DC voltages (using a DMM) at the same points in the two channels you should be able to find the fault even if you are inexperienced.

author: Eurora
author_rank: Contributor
timestamp: August 05, 2025, 02:45:23 am
content: Got it. So basically, I’ll use the normal right channel as the reference, then adjust the left channel voltage until both waveforms match on the audio graph — is that correct?

author: Eurora
author_rank: Contributor
timestamp: August 05, 2025, 02:46:41 am
content: Thanks for the reply! But I'm still itching to ask: why didn’t thermal imaging work? (A friend swears by this method)— Is it 'cause the temp differences weren't different enough?

author: edavid
author_rank: Super Contributor
timestamp: August 05, 2025, 03:58:06 am
content: Quote from: Eurora on August 05, 2025, 02:45:23 amNo. You will measure the difference between the two channels under the same conditions. Then you will use the measurements plus circuit knowledge to determine the failed component(s).(What were you planning to adjust?)Quote from: Eurora on August 05, 2025, 02:46:41 amIt only helps if something is overheating, and there is no evidence of that.

author: Eurora
author_rank: Contributor
timestamp: August 06, 2025, 02:18:33 am
content: This finally makes sense! Seriously appreciate you taking the time to walk a total newbie through it.😂 My half-baked idea to tweak things? Haha, scratch that – just realized it wouldn’t fly. Thanks for steering me right!